Bad Astronomy Blog

Juno Makes Another Pass at Jupiter

9 hours 27 min ago

On July 5, 2016, Jupiter acquired a new moon: NASA’s Juno spacecraft. Launched in 2011, Juno passed by the Earth in October 2013 to pick up some energy and fling itself to Jupiter. Once it arrived, it burned its main engine for over a half hour, slowing enough to place itself into a highly elongated orbit that took it over Jupiter’s poles.

The orbital burn went perfectly, but a potentially serious problem arose. In October 2016, after two complete orbits (each about 54 days apiece), the main engine was scheduled to fire once again. It was supposed to change Juno’s orbit from the initial looping trajectory that took it as close as 4,200 kilometers over Jupiter’s poles to over eight million kilometers out, to the new “science orbit” that was supposed to be only 14 days long.

However, just before the burn, telemetry indicated that a pair of valves had failed to work properly. The orbit reduction maneuver was at first postponed until Dec. 11, 2016, but then it was decided to postpone it again until at least the next perijove (closest approach to Jupiter), which is in February 2017. The spacecraft is working, and collecting good data, so engineers decided it would be better to work the problem longer to make as sure as they can that the maneuver will be performed properly.

The image above is from a few hours after the last pass in December, called Perijove 3 (counting the Jupiter orbital insertion in July as 0, the dip over the pole in August Perijove 1, and October Perijove 2). It shows the south pole of Jupiter to the bottom, and from this vantage we’re looking “up” at the Great Red Spot (which is located at a latitude of about 22° south of Jupiter’s equator). The smaller red storm to the lower right is called Oval BA (no relation), but it’s hardly small: It’s about the same diameter as Earth! It formed in 2000 when three smaller storms merged.

The image was processed by master planetary photographer Damian Peach, and it’s so, well, odd. Jupiter orbits the Sun in roughly the same plane as Earth, and its rotational axis is pretty much perpendicular to that plane. That means, from Earth, we tend to be looking down on Jupiter’s equator, with the belts and zones stretching across horizontally. From this angle everything is tilty; it’s a view we cannot get from Earth. If you want to see Jupiter this way, you have to go there.

Which is another reason Juno is so cool. Another Juno image Peach put together from the raw data graced the Astronomy Picture of the Day site recently as well.

This last pass of Jupiter by Juno was the first to take gravity data. One of the main purposes of the Juno mission is to map the interior of Jupiter. As it passes very close to the planet, the layers of material beneath the surface of the planet pull on the spacecraft differently, affecting its orbital trajectory minutely. These changes can be used to determine the density of those layers, which in turn reveals the internal structure of Jupiter.

Weirdly, it’s not clear if Jupiter has a distinct core or not; different physical models for how it formed yield different results. Juno may be able to help scientists determine which is correct. In the meantime, Juno will pass through Jupiter’s intense magnetic field, returning information about that as well.

Hopefully, over the next few weeks scientists and engineers will be more confident they can put Juno into the correct science orbit. Until then, it’s still doing good work, and we can enjoy the literally unearthly view.

Categories: Astronomy Headlines

Curiosity Finds an(other) Alien Visitor on Mars

Mon, 01/23/2017 - 05:45

The Curiosity rover has been on Mars since Aug. 6, 2102. In the more than four years it’s been there, it’s seen wonders beyond our Earthly reckoning: evidence of ancient flowing water, evidence of ancient standing water, methane in the atmosphere now, carbon in the rocks, dark basaltic sand dunes, weird lumpy moons circling a dusty red planet.

Mars is indeed an alien world. But even with all that, sometimes Curiosity still manages to find things on Mars that are able to surprise and delight: The photo above shows a meteorite sitting on the planet’s surface.

How cool is that?

The picture was taken on Jan. 12, 2017 —the 1577th Martian day, or “sol”, after Curiosity landed—when the rover was investigating sedimentary rocks in the Murray Formation, a large deposit along the flanks of Aeolis Mons (also called Mt. Sharp), which itself is the central peak in Gale Crater. Since landing, Curiosity has been inside Gale Crater, heading toward that central mountain.

The meteorite sticks out like a sore thumb among the rust-colored rocks and darker wind-blown sand. The shape and color just scream “I’m not originally from here!” —just compare it to the mudstone to the upper left, or the flatter rock below it. It’s hard to say exactly, but it’s likely a few centimeters across, perhaps the size of the palm of your hand.

I collect meteorites and have read quite a bit about them, and to my eye this is obviously a metallic nickel-iron specimen. I have some on my bookshelf that look quite a bit like this!

On Earth, meteorites like this one start out as a larger chunk of metal asteroid orbiting the Sun. If it has the bad (for them, good for us!) luck of slamming into our atmosphere at hundreds of thousands of kilometers per hour, the intense pressure fiercely heats the air ahead of it, melting its exterior and causing it and the air to glow. A bigger asteroid (say, the size of an easy chair or a bus) can actually explode as the pressure flattens and disrupts it, sending hundreds or thousands of smaller pieces outward. They can form all kinds of weird, bizarre shapes; folded, twisted and pitted from the huge forces at play.

The atmosphere of Mars is much thinner than Earth’s, but is still thick enough to affect an incoming asteroid in similar ways. I don’t know if this meteorite was part of a larger piece or came in on its own, but the sharp edges and odd surface features betray its extramartian origins.

I’m almost positive this is metallic; stony meteorites tend to look more like, well, rocks. This is clearly more like sculpted metal. The only way to be sure is to get spectra of it… which Curiosity can do! The ChemCam detector was designed specifically to be used for this. It has a high-powered laser it uses to zap rock samples, heating them very rapidly. The vaporized rock emits light that can be broken up into individual colors; different elements in the sample can then be determined by the different colors of light they emit.

In the ChemCam Remote MicroImager photo above, you can see the odd shape of the meteorite, as well as several small, evenly spaced shiny features. Those are laser zap marks! ChemCam took spectra of the meteorite, so hopefully we’ll find out what it’s made of. Unfortunately the actual data won’t be made public for some time, but I’d bet the value of that meteorite* that they’ll find it’s mostly iron and nickel (and maybe cobalt); those are the main constituents of metallic meteorites here on Earth.

I’ll note that meteorites have been seen on the Martian surface before by both of the Spirit and Opportunity rovers, and have even been used to examine surface conditions on Mars now and in the past.

So there’s scientific value in this. These specimens also tell us about the conditions in the asteroid belt, so this is extra science for free. Not only that, but the shape and structure of meteorites might be helpful in understanding what happens to objects as they fall through Mars’ atmosphere at high speed, which has some value as well; after all, that’s how we get our own hardware down to the surface (though meteoroids tend to be moving more rapidly than spacecraft).

Also, it’s just really, really cool.

I have to admit, seeing this photo is odd. My first reaction was to think, “Whoa! A meteorite! How weird!” How silly is that? After all, these are close up pictures of the surface of another world. Is this not enough for my science–drenched brain to fill it to capacity with wonder?

Apparently not. There is still room to be awed, and I’m OK with that.

My thanks to RidingWithRobots for the original tweet about this, and to planetary scientist Ray Francis for the ChemCam photo link.

* The price for nice metallic meteorites varies a lot, but tend to be around a few dollars a gram. Ones from “known falls” —where the meteor event was seen—are more valuable. Given that this one is on freaking Mars its value is beyond price.

Categories: Astronomy Headlines

If You Need Strength Today, Be Like Daphnis

Fri, 01/20/2017 - 05:30

Today is a difficult day. And it’s just the latest in what have been very, very difficult times.

I’ll be honest with you: Over the past few months, in between bouts of fury and incredulity, like so many of you I have felt real despair. Watching the country I love, the people I care about, and the science to which I have devoted my life come under such attack has been extraordinarily difficult and painful.

It can be hard to find any comfort in situations like these. And I have no desire to utter to you any hollow phrases, any meaningless pablum that sounds deep but is of no actual content.

Instead, please indulge me for a moment.

First, read this article I wrote yesterday about Saturn’s moon Daphnis. It may seem like a non sequitur, but as you'll see it’s quite the opposite.

That image of Daphnis I posted yesterday is grayscale, a single picture of the moon taken by the Cassini Saturn probe. The one you see here was crafted by Ian Regan, using two images from Cassini to create a representation of the color. I actually saw his version first, the colors sublime, adding a subtle and delicate touch to the otherworldly vista.

It was in the evening when I first saw it, and I was in bed (perhaps ill-advisedly) checking Twitter before going to sleep. I was stunned… and I mean that literally, as in my brain locked up for a moment as the wonder of this image flowed into it.

For just a moment I wasn’t sure what I was seeing, and by that I mean which of Saturn’s panoply of moons and what part of the rings this depicted. Daphnis is so small that it’s only appeared as a barely resolved dot in previous images, and the detail in the surface features threw me. When I saw Regan’s caption identifying the moon I was stunned anew, since I knew this was by far the highest-resolution photo of Daphnis we’ve ever seen, and likely ever will.

The more I gawked at this photo the deeper my awe became. The ripples, the structures, the graininess of the rings, the smooth(ish) surface of Daphnis, the ringlets that are so narrow they challenge the ability of Cassini to resolve them, and most of all that gossamer thread of ring pulled away by the feeble gravity of this diminutive moon… all of this was a fantastic delight, a gift literally sent down from the heavens.

As I struggled to tease out the details of what I was seeing, a thought struck me: Daphnis was only discovered in the year 2005. Its presence was first suspected in 2004, when Cassini returned images of waves and spikes in a gap in Saturn’s rings, obviously sculpted by a tiny moon, though its exact location was at the time unknown. Observations were quickly planned to get better images of the gap where the ripples were seen, and in May 2005 astronomers announced they had found it. It was given the name Daphnis the very next year.

And here we are, a dozen years later, with a new and extraordinary view of this odd little satellite. As I lay in bed and mulled over that, a thought struck me. We’ve known about this moon for a decade or so, but how old is it? Millions of years? Billions? How long has this tiny chunk of ice been circling Saturn, carving these marvelous creations out of still tinier chunks of ice?

As I chewed on this, an honest-to-god chill went down my back. This moon has been silently gliding through Saturn’s rings since before humanity existed as a species, and likely far, far longer. It’s done this without notice, without discovery, without supervision, without any sense of purpose or any eyes seeing it.

Daphnis did what it does because it must. It follows the rules of science, dancing to the tune of gravity, and it wasn’t until just a few years ago that we too could read those notes, hear that music, and appreciate its melody.

Daphnis is so small you could circumnavigate it by foot in a few hours, provided you could maintain your traction in its faint whisper of gravity. Yet, in the vastness of Saturn’s rings, almost completely lost among a trillion, trillion particles, it still manages to make waves, to reach out and create an effect, to stir echoes in a system far larger than itself.

And when we ponder the reverberation of those echoes, they engender in us a sense of beauty. Of awe.

All of these thoughts were still ringing in my mind when I happened to see how my friend, astrophysicist Katie Mack, was herself inspired by this image from over a billion kilometers away, and how she captioned it.

Yes, these are trying times, and it is easy to feel overcome, to be overwhelmed by events. And yes, the Universe itself is telling you that you are small. But do you know what else it’s telling you?

You are mighty.

Go out and make a difference. It may be a small one, but its reach may be profound, and extend far beyond what you intend or might perceive.

Go. Be like Daphnis.

Categories: Astronomy Headlines

Saturn's Moon Daphnis Creates Spectacular Ripples in Saturn's Rings

Thu, 01/19/2017 - 05:45

When I saw the image above, I literally gasped. It’s an amazing photo, showing the small moon Daphnis inside a gap in Saturn’s rings. The beauty of this shot is apparent, but the science behind it is even cooler.

Allow me to explain.

On Nov. 30 of 2016, the Cassini spacecraft orbiting Saturn took on a new and risky mission. It began a series of orbits that are taking it over the planet’s north pole and then down just outside the main rings.

In mid-January 2017 it dipped through the ring plane on one of these orbits, passing a mere 28,000 kilometers from the tiny moon Daphnis when it took that shot with its narrow-angle (i.e. high-magnification) camera.

That’s the highest-resolution image of Daphnis ever taken; for scale, the flying-saucer-shaped moon is about 8 x 8 x 6 km in size. Measured from sea level, Mount Everest is roughly the same size. You can see some structure to Daphnis; there’s a ridge around its equator that’s probably due to ring particles that have piled up there, and a second ridge at higher latitude. The soft appearance to the moon is probably due to the accumulation of small grains of ice from the rings that have coated it, filling in the craters and other features.

That gap in the rings is real. It’s called the Keeler Gap, and it’s about 30-40 km wide. The width of the gap appears foreshortened because Cassini was just above the ring plane when it took the shot; it’s actually several times wider than the moon is long.

But, oh, those ripples! That, my friends, is the result of gravity. It’s a complicated and intricate dance between moon and rings, but it’s worth learning the moves.

Saturn’s rings are composed of countless tiny particles of ice, each in its own separate orbit around Saturn. They’re tremendously wide —the main rings are 300,000 km across, and would stretch 3/4 of the way from the Earth to our own Moon— but are astonishingly flat. In some places they are only 10 meters high from top to bottom, the height of a three-story house. To scale, this makes them far thinner than a piece of paper.

There are several subdivisions of rings, given letter designations in order of discovery. The broad A ring has distinct two gaps in it, carved by moons orbiting Saturn embedded in the ring. The Encke gap is 325 km wide, and is from the moon Pan. The much narrower Keeler Gap is due to Daphnis.

If you plunk a small moon down in a ring, it will of course carve a gap as it plows through material. Its gravity will attract more material as well, so particles just inside and outside the moon will, over time, fall onto it. The gap grows, but the width of the gap depends on the strength of the moon’s gravity. At some distance, the gravity is too feeble to pull particles all the way out of the ring and onto the moon. Pan has nearly 100 times the mass of Daphnis, so its gravity is stronger, and the gap it carves wider.

What causes those ripples? The orbit of Daphnis is not a perfect circle, but instead is very slightly elliptical. That means it’s sometimes closer to the inner edge of the Keeler gap, and sometimes closer to the outer one. The change is small, only about nine km, but that’s enough. When it’s closer to one edge it pulls on the ring particles a bit harder, creating the wave.

But there’s more to it. The orbit of Daphnis is also tipped a bit to the ring plane, a mere 0.0036° from being exactly aligned. That means it bobs up and down out of the ring plane by about 17 km. When it does it drags the ring particles at the gap edges as well. Those waves you see in the image go in and out of the gap, but also up and down by a kilometer or so.

Perspective makes that hard to see here, but twice every time Saturn orbits the Sun, the rings are edge-on to the Sun, and any vertical excursion can cast long shadows.

That image was taken at Saturn’s northern hemisphere spring equinox in 2009. It’s incredible! You can see Daphnis and the long shadow it casts on the ring. You can also see the vertical waves caused by the moon’s feeble pull. Each wave corresponds to one up-and-down bob of the moon relative to the rings. Eventually, tides from Saturn pull the particles back down, but that takes a while, and the ripples extend for a long way around the ring.

How about that? But wait! There’s more!

Look again at the first picture. You can see the ripple to the left of Daphnis is fuzzier than the others. That may be due to very tiny grains being pulled out (that ripple is on the outside of Daphnis, so was created the last time Daphnis passed those particles). The particles are brighter there than on the ripple right next to Daphnis, which is interesting; that may be due to the Sun’s illumination on the wave.

That’s a closer look at the top photo. You can see a very thin ribbon of material to the left of Daphnis. That may be due to a clump of material in the ring that was pulled apart by the moon! Note the shape, too; it mimics the ripple but looks like it goes deeper into the gap. Amazing. When I saw that I had to sit back and stare in awe. I don’t think anything like that has ever been seen before.

Also in that shot you can see the rings look grainy. That may very well be a hint of the actual grainy particulate nature of the rings, where material has clumped up! Cassini is getting closer to the rings than it ever has before, so we see them in more resolution. I hope we get even better shots of them over the next few months.

We’d better, because time is running out. Cassini’s end-of-mission is in September of this year, and when it’s done engineers will command it to plunge into Saturn’s atmosphere, where it will burn up and be crushed. This is done to prevent any possible contamination of the moons in case Cassini might impact them in the future after fuel has run out. Instead, the remaining wisps of fuel will be used to send the probe into the planet itself.

I’ll hate to see Cassini go. But images like the ones of Daphnis make me glad we had Cassini for as long as we did. It’s a truly historic mission, and its legacy will live on for a long, long time.

Tip o’ the RTG to Ian Regan.

Categories: Astronomy Headlines

2016 Was the Hottest Year on Record

Wed, 01/18/2017 - 07:41

Well, it’s official: 2016 was the hottest year globally on record.

The National Oceanic and Atmospheric Administration released its numbers for the year, and there’s no way to sugarcoat this: It’s bad.

We've had three consecutive years of record-breaking heat all over the planet.

Looking at land and ocean temperatures, the NOAA finds that the planet in 2016 was the hottest since records began in 1880, with a global average temperature 0.94°C (1.69°F) above the 20th-century average of 13.9°C (57.0°F). That may not sound like much, but it’s actually huge.

Think of it this way: The surface of the Earth is about 200 million square kilometers. All of that, everywhere, is now nearly a degree hotter than it was in the previous century. That’s a vast, staggering amount of extra energy.

Update, Jan. 18, 2017 at 16:20 UTC: NASA's Goddard Institute for Space Science and Berkeley Earth also released their results, which agree with NOAA: 2016 is the hottest year ever recorded.

As the planet warms, you’d expect the land to heat up faster than the ocean; water responds more slowly to changing temperature. And that’s just what we see: The land only temperature was 1.43°C above the 20th-century average, and the ocean-only temperature was 0.75°C warmer. Both are records; the land temperature easily surpassed 2015, though the ocean temperature was only a bit more than the previous record.

Normally, I’m not too concerned with breaking records; sometimes you get fluctuations due to statistics that can edge out a previous high mark. But in this case it’s different, because we’re talking about a hugely sampled number of temperature measurements taken over a substantial amount of the Earth’s surface.

But what makes this far more worrisome is the trend. If it’s getting hotter, you’d expect the hottest years to be the more recent ones, of course. Well, from the NOAA rankings, 15 of the 16 record hottest years were from 2001–2016, with 2016 being the hottest. Before that, 2015 was the record holder, and before that it was 2014.

The world is heating up.

There’s more. To wit:

  • Sea ice in the Arctic has been declining precipitously for some time, but this past year took a huge dip. The average extent for 2016 was about 10 million square kilometers, the lowest on record.
  • Record high temperatures were seen all over the planet. Tellingly, no land areas were cooler than average. It was hotter everywhere over Earth's solid surface.
  • 2016 was the second hottest year on record for the contiguous United States, with every single state getting above average temperatures.
  • The lower and middle troposphere (the atmosphere from the Earth’s surface up to about 10 km, though it varies by latitude) also saw record high temperatures.
  • The stratosphere (the atmospheric layer above the troposphere) saw record cold temperatures, but ironically this is exactly what you expect from global warming (you can get more details of why that is at Real Climate and Yale Climate Connections).

Global warming is real, and it’s happening now, and it’s our fault. The overwhelming majority of climate scientists agree with this. Peter Gleick, a scientist who studies the impact of global warming, puts it this way: “Not a single national science academy disputes or denies the scientific consensus around human-caused climate change.” And not just in America, but all over the globe.

Of course, some politicians disagree. And to the detriment of all humanity, many of them are currently in power in the United States, and are about to consolidate that power more. Nearly every single Cabinet nominee Donald Trump has chosen denies the reality of global warming. As my friend and science advocate Sheril Kirshenbaum noted, just getting one of Trump’s appointees to admit that climate change isn’t a hoax is surreally encouraging.

In a world heating up, that’s a tepid victory.

There is some good news, or at least less bad news. President Obama just sent $500 million to the United Nation’s Green Climate Fund, a program to help developing countries—which tend to be the hardest hit by climate change—adapt to this new world. That’s great, but he did it on his way out, and what’s coming in is an administration hellbent on tearing down any legislation to help mitigate global warming that’s been enacted the past eight years.

For example, the House Committee on Science, Space, and Technology still has a GOP majority, and they just added several new reality-denying members. I have little doubt that Rep. Lamar Smith, R-Texas, the committee chairman, will continue his baseless attacks on climate scientists, and I’m sure he will issue a challenge to this newest NOAA hottest year finding, just as I’m sure it will distort the facts. That’s been his modus operandi for years.

Still, there’s hope. I’ve said it before: We need a public that’s excited about science. Most people in America know climate change is real, and want the government to take action about it. The next two years will be very difficult, but then there’s the midterm congressional election. Two years after that is the next presidential election. These elections have consequences, and right now those consequences are more than 700 days of climate inaction, if not outright hostility. We need to be ready to fight legislation taking aim at making our planet hotter, and be ready to throw out our representatives if they deny the science.

Never forget that word: our. They represent us. And if we chose it, then we can put science-friendly legislators back in power. It will literally save humanity.

Categories: Astronomy Headlines

Apollo Astronaut Gene Cernan Has Died at 82

Tue, 01/17/2017 - 05:45

Apollo 17 Commander Gene Cernan has died.

Besides being a Naval aviator, a fighter pilot, and an engineer, he is best known as the last human to have stood on the surface of the Moon.

Like every other astronaut of the time, Cernan was quite the character, with a storied life. He had been an Aviator for five years when, in 1963, NASA tapped him to be an astronaut. In 1966 he commanded Gemini 9A, the pre-Apollo mission for which he was part of the backup crew before the prime crew died in an airplane crash. Gemini was a precursor to Apollo, a way for NASA to learn the skills needed for the mission to the Moon.

9A had a series of mishaps itself. Its primary mission was to rendezvous and dock with an uncrewed vehicle that was to be launched hours earlier, but that rocket failed during flight. A second uncrewed vehicle was launched successfully two weeks later, but on its first attempt, the rocket with Cernan and Thomas Stafford suffered a malfunction and didn’t launch. It finally went up two days later.

Things still went poorly. Once in orbit they found the rendezvous vehicle slowly spinning (and a shroud had failed to jettison, making docking impossible). Cernan’s extravehicular activity (EVA) was postponed until the mission’s third day. Even then he had serious problems with his suit, and the two-hour EVA exhausted him. They had to cut it short, but he was so overheated and tired there was real concern he wouldn’t be able to get back into the capsule. He did, of course, and NASA eased up the workload of future missions to prevent overtaxing the astronauts.

I cannot stress enough how difficult that Gemini 9A EVA situation was, and how hard Cernan pushed himself to get done what had to be done. I suggest reading the Wikipedia entry for the mission to get a flavor of it, and to let the word “hero” be fixed in your mind as you do.

Six years later, on Dec. 7, 1972 he commanded Apollo 17, and despite everything else he did to earn his mark in history, this will be forever why we remember him. You can read about its exploits in many places; I suggest you pick up a copy of my friend Andy Chaikin’s book “A Man on the Moon”, which, in my opinion, is the single best written history of the Apollo program. Cernan (along with co-author Don Davis) wrote about this as well in his book “The Last Man on the Moon”.

About that mission…

At 05:40 GMT on Dec. 14, 1972, a week after he left Earth and after completing three successful lunar EVAs with his fellow crewmember Jack Schmitt, Cernan stood on the surface of the Moon, preparing to go back up the ladder and get back inside the Lunar Module. Just before he did, he said,

I'm on the surface; and, as I take man's last step from the surface, back home for some time to come – but we believe not too long into the future – I'd like to just (say) what I believe history will record: that America's challenge of today has forged man's destiny of tomorrow. And, as we leave the Moon at Taurus–Littrow, we leave as we came and, God willing, as we shall return, with peace and hope for all mankind. Godspeed the crew of Apollo 17.

He then climbed aboard the LM, and in that moment became the last human to stand on the Moon.

For now.

Cernan’s family released this statement upon his death:

Even at the age of 82, Gene was passionate about sharing his desire to see the continued human exploration of space and encouraged our nation's leaders and young people to not let him remain the last man to walk on the Moon.

Cernan himself did not wish himself to hold this place in history, and pushed for NASA to go back to the Moon. All these years later we still haven’t, but that will not stand. China and India have both said they want to send people to the Moon, and Russia has made similar claims.

NASA has set its sights on Mars, but I still hope we go back to the Moon first, doing something similar to Gemini before Apollo: Use our more advanced technology to learn about how we can achieve human deep-space flight better, and most importantly, more sustainably. Apollo, as heroic and historic as it may have been, was, after all, a “flag and footprints” mission, designed to get there before the Soviets did. A race to the finish cannot be a long-term plan. We must commit to going back, and doing it to stay.

I remember the Apollo missions, barely. I was a child at the time. But I hope that within my lifetime I will see a wonderful thing: Another human stepping out of a lander and dropping down onto the surface, a puff of regolith dust arcing out ballistically from their boots in the airless environment.

And when this happens, we will update our references to Commander Cernan, adding the words “… of the Apollo era” to his descriptor, “the last human to walk on the Moon.” At that moment he will become the last of the first, and, with our eyes open and our dedication firmly in place, there will never be another last.

Categories: Astronomy Headlines

SpaceX Returns to Flight

Mon, 01/16/2017 - 05:45

Over the weekend —on Saturday, Jan. 14, 2017— SpaceX launched a Falcon 9 into space, successfully completing its primary mission of deploying ten Iridium communication satellites.

The secondary mission? To land the first stage booster on a drone ship in the Pacific. And that happened perfectly:

How cool is that? What happened is that after boosting the second stage toward orbit, the first stage flipped around, performed an engine burn to slow down, flipped again, deployed the steerable grid fins, then (after much shorter burns of the main engine and some help with cold jets for attitude control) landed smack dab in the center of the drone ship Just Read the Instructions (the barges are named after sentient ships in the science fiction novels of Iain M. Banks)*. This was the first successful landing of a booster in the Pacific Ocean; an earlier attempt in January 2016 came close, but one of the landing legs failed to lock, the booster fell over after the soft landing, and then exploded (and you want to click that link; the video is really something)

This mission was important, marking the return-to-flight status for SpaceX after an explosion during fueling of a Falcon 9 in September 2016. SpaceX traced the cause of that to a liquid helium tank in the second stage.

As my colleague Eric Berger at Ars Technica writes, the helium tanks are mounted inside the liquid oxygen tanks; as the oxygen is used up during launch, helium is released to maintain pressure in the tank. However, the carbon fiber wrapping of the helium tanks appears to have buckled in the extreme cold environment, letting oxygen in between the coating and the tank itself. Liquid oxygen isn’t flammable, but when it contacted the much colder liquid helium tank it froze and combusted, causing the explosion. To prevent this from happening again, they’re returning to their “flight proven configuration” of the tanks for now (an older setup with warmer helium), and in the future will change the fiber wrapping to prevent it from buckling.

Berger also has an interesting article about SpaceX’s finances; they lost quite a bit of money ($250+ million) in the 2015 accident where a rocket was lost on its way to the space station, but still has ambitious plans for more than two dozen launches this year alone. That includes tests for the first crewed flight, and the first flight of the Falcon Heavy, their next-generation rocket that will be the most powerful rocket in the world… though Blue Origin has their goals of building some pretty big boosters as well.

This should be a pretty exciting year for space exploration. Let’s hope it all goes well. In the meantime, congratulations to SpaceX for getting the planet underneath them once again.

Correction, Jan. 16, 2017: I originally had embedded the wrong video, it was from an earlier launch (I see a lot of people have done the same thing, too).

Categories: Astronomy Headlines

Give Me Your Tired, Your Poor, Your Huddled High-Mass Stars…

Fri, 01/13/2017 - 05:45

Let me tell you something funny about that picture above.

Somewhere between 7,000 and 10,000 light years away —estimates vary— lies the huge nebula NGC 3576. It’s very roughly 75 light years across, making it one of the bigger star forming regions in the galaxy.

And that’s just the visible part of it. It appears to be part of a larger complex of dark, dense gas as well, which is pretty typical of such objects. But the part we do see is impressive enough: It has 10,000 times the mass of the Sun just in hot gas, and glows at a fierce 10 million times the brightness of the Sun as well. Many hundreds of stars are in the process of being born there, making it a fairly fecund stellar nursery.

Those giant loops above and to the left are made of gas probably compressed by the winds of the massive stars born in the nebula; they blast out fierce streams of subatomic particles, far stronger than the solar wind, and combined slam into the surrounding gas to push it away.

Interestingly, there’s some evidence that star formation in the nebula was triggered, perhaps by the collision of another cloud or due to an exploding star. This drove a shock wave through the gas and dust, causing them to collapse to create stars. There are more younger stars to the east (left) then the west, so perhaps the triggering event came from that direction.

And while all of this is pretty cool, none of that is the reason I wanted to write about this object. The actual reason is because of the dark blobby clouds in the center. Those are denser regions, where the dust is thicker. Stars are probably being born in there as well, protected from the harsh environment of the rest of the nebula outside those clumps.

But it’s not the science of those dark clouds so much as their structure. By pure coincidence, they form a shape strongly reminiscent of the Statue of Liberty!

Do you see it? The long trunk on the left is the upraised arm of the statue (where she holds the torch), and the shorter one on the right is her head. It looks lke gas streamers are her gown, and there are even stars for eyes. If you look closely it also looks like she’s wearing a crown! That’s actually gas and dust being zapped by high-energy light from massive stars; the ultraviolet radiation break apart molecules, heats them up, and causes them to flow away in streamers. That’s typical at the edges of dense dust clouds embedded in star-forming nebulae, and this erosion is why you get those long trunk-like features in the first place. They’re like cosmic sandbars in the gas flow.

The image above was taken by a team led by Steven Mazlin. Although the nebula is well-studied, and numerous images of it exist, Mazlin noted that it didn’t have a common name, like how we call M16 the Eagle Nebula, or NGC 1976 the Orion Nebula. So he proposed the Statue of Liberty Nebula, and I have to say, that works for me. The resemblance, once you see it, is pretty good!

The name is informal, but this object can now join the Bald Eagle Nebula, the Hummingbird Galaxy, and my favorite, the Flaming Skull Nebula (well, that’s what I call it, but c’mon, look at it!) in our menagerie of unofficial but obvious-when-you-see-them named objects in the sky.

I should make a list. There are a lot! Pareidolia —seeing faces and familiar shapes in objects— is a very strong psychological effect, and the patterns in nebulae and galaxies are tantalizingly familiar. It’s fun to project ourselves into the sky, and in most cases it also tells us just as much about ourselves as it does the object in question.

Tip o’ the lens cap to APOD, where I first saw this.

Categories: Astronomy Headlines

The Clouds of Andromeda

Thu, 01/12/2017 - 05:45

The image above is as baffling as it is gorgeous.

First, kudos go to my pal Rogelio Bernal Andreo, who took this magnificent shot. It shows the Andromeda Galaxy, the closest big spiral galaxy to our own, and in fact the other big member of our neighborhood galaxy minicluster called The Local Group. At 2.5 million light years away, it’s bright enough to see with the naked eye from moderately dark sites, and shows quite a bit of detail even through small telescopes.

Rogelio’s image is unusual. First of all, it shows a huge area of the sky; Andromeda is several times the apparent size of the full Moon on the sky (see here for a comparison). Hold up your hand, and fold in your pinky and thumb; the width and length of your three middle fingers extended at arm’s length would be about the same area of sky as the photo.

The image is a composite of “natural” color imaging using red, green, and blue filters to mimic what we’d see with our eyes, together with a “luminance” or white-light image, taken with no filter. That adds detail and depth to the image; together astrophotographers call it an LRGB image.

But there’s more. He also took many hours worth of observations using a filter that lets through a very specific wavelength, or color, of light. This red light, called Hα (literally, “H alpha”) is emitted by warm hydrogen gas. Since hydrogen is so common throughout the Universe, an Hα filter is very useful; you can use it to accentuate nebulae and galaxies.

The red clouds in the image are hydrogen nebulae. They’re extremely faint; Rogelio had to work very hard to make them visible above the background light of the sky. In the photo their brightness has been magnified by a substantial amount, so the image isn’t “natural” in that sense; if Andromeda had been scaled on the same brightness range as the clouds the galaxy would be vastly overexposed, a huge white blob blotting out everything around it.

So the image isn’t really what your eyes would see through a telescope, but has been adjusted to show these two very different views simultaneously. Still, it’s beautiful for sure… and very odd.

The big question is, what are those clouds?

On his website (and in a follow-up on his Facebook page), Rogelio describes his observations, their history, and his research into the glowing clouds. He points out he loves chasing faint, diffuse clouds. Called galactic cirrus (or the fancier Integrated Flux Nebulae), these are generally very thin streamers of dust —grains of silicates or long carbon molecules— strewn throughout space inside our galaxy. They’re exceedingly faint, and difficult to image. But if the dust is warm it can glow in infrared. So Rogelio checked professional observatory infrared images of that area in the sky, but the clouds seen in them don’t fit well to what he observed. That seems to rule out galactic cirrus.

However, he did see them, barely, in a pair of surveys that mapped the sky in Hα. He shows this on his page, and looking at them I’m confident these clouds are real, and consist of glowing hydrogen.

Rogelio also argues, and I agree, that the clouds aren’t physically associated with the Andromeda galaxy. At that distance those clouds would have to be huge, tens of thousands of light years across, far too large to make any sense. We do see clouds of gas this big in the Universe, but generally speaking they don’t display the structure in the image. For example, that one above the galaxy near the top center shows a long, flat, bright edge. Features like that are common in smaller gas clouds a few light years in size. You get them when an expanding (or rapidly moving) gas cloud hits material outside it. The gas piles up, forms a sharp edge, and gets denser and brighter. But something like that would be highly unusual, to say the very least, in a cloud of galactic size.

So clearly these are gas clouds inside our own Milky Way, and we’re looking through and past them to the much more distant Andromeda galaxy. But that’s still odd. Nebulae like that are usually heated up and lit by nearby massive stars. The stars emit ultraviolet light which pumps energy into the gas, and it responds by glowing like a neon sign (literally). But I don’t see any stars close by that could do that.

So why are they glowing?

Given the lack of nearby luminous stars, my first guess was that they are colliding with lower density gas around them. That would explain the one cloud with the sharp edge, but the others are even more diffuse, so I’m not sure that explanation works for them.

I have another idea. Perhaps there’s enough ambient ultraviolet light from massive stars spread out in space that, combined, they can cause these clouds to softly glow. This would be a sort of background UV light, very faint, but enough to trigger the nebulae into emitting Hα light. While that’s a guess, it seems plausible… and I don’t see anything else that makes much sense.

Let me say here that I love this. Andromeda is one of the best studied objects in the entire sky, yet here are objects in the same field of view that have essentially escaped notice all this time. That’s understandable; Andromeda is so bright that faint clouds are ridiculously hard to see, but our technology and techniques are getting so good that the previously hidden is becoming revealed. And on top of that, it also took the dedication of someone like Rogelio to pursue this.

The next step, I should think, is to find a research astronomer who can take an interest in this and get even deeper images and take spectra of these clouds (to determine their chemical composition as well as motion, which can help nail down their distance). There are lots of fascinating questions to answer here. How common are these clouds? How old are they —are they recently cast off by dying stars, or primordial, dating back to when the galaxy was young? Are they everywhere in the sky, or do they tend to be clumped near the galactic plane? And to me, the most interesting question of all: What’s lighting them up?

They’re certainly lighting me up. I hope we can find out more about these elusive beasts soon.

Categories: Astronomy Headlines

Talk Nerdy: Anti-Science, Trump, and Why I Hope Science Will Help Save the World

Wed, 01/11/2017 - 07:53

Funny how things work out.

I had already drafted an article about an interview I did over the weekend with my friend Cara Santa Maria for her Talk Nerdy podcast. We spent a lot of time talking about critical thinking, science, and Donald Trump.

And then, as I was editing that article, a whole passel of revelations came out about Trump. By now you’ve probably heard about the intelligence reports reporting ties between Russia and Trump's campaign to manipulate the presidential election.

Almost lost in all the noise over that was that Trump had a meeting with Robert F. Kennedy Jr., purportedly asking him to be on a panel on the safety of vaccines. I have written about RFK Jr.’s crackpot anti-vaccine stance many times (see, in order, this article, then the follow-up, and then a third one). His views are wrong, anti-scientific, and downright dangerous.

All of which makes this interview all that much more timely and, if I may say so, important. Please give it a listen.

Cara had me on her podcast back in 2015, and asked me to be on again because she happened to see my name in the credits of the movie Arrival, and wanted to know what my involvement was (spoiler: I made some minor comments on the script before it was finalized). The first half of the podcast is about that as well as the influence of science in movies and TV.

But then we spent quite a bit of time talking about Trump and his predilection for anti-science. As an easy example, his incoming Vice President Mike Pence and Cabinet picks Rick Perry and Ben Carson are all young-Earth creationists. Trump’s nominees are all basically the worst people a rational person would pick for those positions.

And while you might argue that someone being a creationist doesn’t disqualify them from being secretary of energy, for example, it does show Trump’s egregious propensity to actively seek out people who deny science for positions of power. The meeting with RFK Jr. just confirms that.

So. The big question is, is there hope?

Yes, I think there is. And it may come from an unlikely direction.

Cara ends every podcast asking her guest two questions: What is your biggest fear for the future, and what is your biggest hope?

My answer this time was similar to the last time I was on her show: climate change and science, respectively. But I generalized it a bit this time.

Certainly climate change on its own is terrifying; I’ve written many times how it’s the single greatest threat we as a species face right now, and how denying it is a threat to our national security. But it’s more than that. The denial of human-induced climate change is just one symptom of the much larger suppression and active antagonism toward science, especially with the incoming Trump administration.

Yet I still have hope. Why? Because there are tens of millions, hundreds of millions, of Americans who are still reality-based. The majority of us understand that climate change is human-caused and a real threat. That means science can still prevail over politics and personal ideology.

In his farewell speech Tuesday night, President Obama said this:

Politics is a battle of ideas; in the course of a healthy debate, we’ll prioritize different goals, and the different means of reaching them. But without some common baseline of facts; without a willingness to admit new information, and concede that your opponent is making a fair point, and that science and reason matter, we’ll keep talking past each other, making common ground and compromise impossible.

Science is a critical piece of that common ground. We need people to be more comfortable with science, which means exposing more of them to it. Even more importantly they need to understand scientific thinking: being critical of sources, data, and conclusions; questioning the process all along the way; and looking for personal biases that might lead to incorrect conclusions.

And that’s why I answered Cara’s last question the way I did. One way to get people to see science is to get it into all aspects of modern culture. Two of the biggest influences on society are TV and movies, and that’s why I’m so happy to see science and scientists being portrayed better in those media. It may seem fatuous, but I contend that it’s an excellent place to start. Like it or not, people, especially younger ones, consume a lot of entertainment. If we show them stories where scientists are just like them, where science is important, where it’s fun, where it can help, where it can save us all, then we still have a chance here.

We have a long, long way to go, and the next two to four years will be trying indeed. But we can do this. Make your voice heard, and make it a voice for science. As long as there are people who would tear down the fabric of reality, there will be those of us who will give their all to defend it.

Categories: Astronomy Headlines

My God. It’s Full of Black Holes.

Tue, 01/10/2017 - 05:45

The image above doesn’t look like much at a glance, does it?

Look again. What you’re seeing are thousands of black holes. Thousands.

That image is a part of the Chandra Deep Field South, the result of a series of very long exposures of one small section of the sky using the space-based Chandra X-Ray Observatory. Astronomers combined images taken over the 18-year period from 1999 to 2016, creating a stacked image that’s the equivalent of a single 7,016,500 second exposure. That’s over 81 days.

So yeah, it’s a deep image. The entire Deep Field image covers roughly the area of the full Moon on the sky using multiple pointings of the telescope. The center of the field has the most observations and is therefore the most sensitive; the image above shows that inner portion of it.

Everything you see in that image is a source of high-energy X-rays —a form of light like the kind we see but with far, far higher energy. Each dot represents the X-rays from an entire galaxy, some over 12 billion light years away! The light we see from those most distant galaxies left them when the Universe itself was only a little over a billion years old.

Only very powerful astronomical objects can generate strong X-ray emission, and the X-rays from the galaxies in the Deep Field are coming from one or both of two very luminous sources: high-mass X-ray binary stars, and supermassive black holes.

The binaries are pretty cool. Many very massive stars are born in pairs, which orbit each other. After a short time, one of them can explode as a supernova, and its core collapses to become an ultra-compact neutron star or a black hole. This compact object can feed off material from the “normal” star; as that stuff falls down into the tiny companion’s ferocious gravity it can heat up to millions of degrees and emit X-rays.

One important part is that these binary systems are young. These stars are so massive they use up their nuclear fuel in the blink of a cosmic eye, perhaps a few million years. That’s critical, because these stars are born in gigantic gas clouds that form lots of stars. By adding up all the X-ray emission we see from high-mass binaries we can calculate how many there are in a galaxy, and from that extrapolate how many stars are being born in total. That tells us a lot about the conditions in galaxies, and in really distant galaxies we can then see what they were like when they were very young.

Our galaxy was very young once, but we only see it now, after it’s over 10 billion years old. By looking at distant galaxies we can better understand how our own was formed.

But that’s only half the story. In the center of every big galaxy today we think there lurks a supermassive black hole, a beast with millions or even billions of times the mass of the Sun. That’s still small compared to the host galaxy (the Milky Way has a mass of hundreds of billions of times the Sun), but that supermassive black hole is important. We’ve found that the mass of the central supermassive black hole in the galaxy is correlated with galactic characteristics like the total mass, luminosity (how much energy it emits), and rotation. These are hard to measure directly in distant galaxies, so by looking at their central black holes we can learn more about the galaxies themselves.

The Milky Way’s black hole isn’t currently feeding, so it’s relatively quiet. But in other galaxies the black holes are eating, and when they do that matter piles up in a disk and can reach temperatures of millions of degrees due to friction and other forces. That’s hot enough to blast out X-rays, which is why we can see them in the Chandra image.

That’s why this deep observation is so important! By examining the X-rays from each source we learn a lot about the galaxy that emits them, far more than simply how much X-ray light they’re blasting out.

Remarkably, astronomers were able to see X-rays from galaxies more than 12.5 billion light years away, the farthest ever reliably detected. Also, they did not see X-rays from galaxies even a bit farther than that (about 12.6 billion light years), suggesting either those sources are too faint, or that it was around that time (1.2 billion years after the birth of the Universe) that these sources started turning on, or that they are so obscured by dust in the host galaxy we can’t see them.

The scientists estimate that roughly 70 percent of the objects in that image are supermassive black holes, and in the whole image there are about 5,000 sources. Imagine: Thousands of black holes in just that one tiny part of the sky! Extrapolating to the whole sky, astronomers estimate there must be over a billion supermassive black holes out in the deep Universe that Chandra could see. A billion.

That’s a lot of black holes. And it’s actually only a tiny percentage of what’s out there; there are hundreds of billions or even trillions of galaxies in the Universe. Each may have its own central black hole, but we just don’t see them (because they’re quiet, or feeding but still too faint to see at large distances).

And that’s just the supermassive black holes. Ones with lower mass, formed when stars explode, probably number in the many millions per galaxy. Extrapolating that means there are quadrillions of black holes in the visible Universe. More.

Holy cow. The good news is they’re far away, and don’t pose any sort of threat to us. And in reality, instead of being scared, you should be thankful: Galaxies and black holes form together, so the Milky Way being here the way it is today is due to its central supermassive black hole. And massive stars exploding seed the Universe with heavy elements like iron, calcium, and other ingredients necessary for life to form. They may leave behind a black hole after the supernova, but they also made it possible for us to be here at all.

It’s a weird Universe indeed where we owe our existence to these cosmic devourers. But, literally, that’s where we are. And that’s why I love this Chandra image and research so much. It tells us so much about ourselves and how we came to be.

Categories: Astronomy Headlines

A Distant View of Home

Mon, 01/09/2017 - 05:45

When I saw the image above, the hair on the back of my neck stood up. Recognize them? Those are the Earth and Moon, as seen from Mars.

That image was taken by the phenomenal HiRISE camera on board the Mars Reconnaissance Orbiter, which was more than 200 million kilometers from Earth at the time. It’s actually a composite of a few separate images, processed to show the relative size and position of our planet and its moon.

HiRISE normally points down to take amazing images of the surface of Mars; it can resolve objects less than a meter across! But it sometimes is pointed at Earth to take calibration images; Earth has known characteristics like color and reflectance that make it a nice test subject for the camera. The image above is composed of ones taken in near-infrared, red, and blue/green, and that’s displayed as red, green, and blue here. Vegetation is highly reflective in near IR, so continents look red; Australia is in the center and Southeast Asia to the upper left. Antarctica is the bright white patch to the lower left.

Also, the contrast has been changed; the Earth is on average more than three times as reflective as the Moon. At the contrast scale Earth is displayed at, the Moon would be almost black, so the brightness of the Moon image has been increased. In this image, you can clearly see features on the Moon, the darker basaltic scars from ancient giant impacts.

This image was taken on Nov. 20, 2016. At the time, the Earth, Sun, and Mars made an isosceles triangle, with Mars at the narrow angle. From Mars, Earth appeared half-lit, at “first quarter,” if you will. From Earth, the Moon was at third quarter, half lit by the Sun and approaching its new phase. That puts the Moon on the far side of Earth as seen from Mars, about 300,000 kilometers farther away. But that’s a drop in the 200 million kilometer bucket, so for all intents and purposes they’re at the same distance. This means the scale of this is right; the Moon is ¼ the size of Earth.

It’s amazing to think that’s home, that we can see our planet and its attendant satellite from so far away. We’ve seen it from farther, of course, including the famous Voyager 1 Pale Blue Dot image (the Moon is invisible in that one), and others taken by the Cassini spacecraft orbiting Saturn and MESSENGER at Mercury (though that last one, I think, was from closer). But in this case, it’s the tantalizing detail that makes it so eerie; there’s just enough there to remind us of home, but not quite enough to make it easy.

Would you have known that was Australia without it having been pointed out? I’m not sure I would have.

It makes me think that there will come a day, perhaps not too long in the future, when we will have an image like this, but it won’t be of the Earth and Moon, or any planet in our solar system. It’ll be an exoplanet, an alien world orbiting an alien star. When that happens, will we see fuzzy continents, pixelated oceans, or a blobby moon?

Categories: Astronomy Headlines

That's No Ordinary Taco. It's a SPACE Taco.

Fri, 01/06/2017 - 05:45

People ask me a lot of questions. One of the most common, understandably, is, “Would you like to go to space?”

My answer is always the same: “I’d like to be in space, but I don’t want to go to space.” The difference being the idea of strapping myself into a chair on top of a 50-meter-high stack of explosives isn’t my idea of fun.

But my answer is a bit of a cheat anyway. Honestly, I don’t even want to be in space. I’d love to soar over Saturn’s rings, orbit low over an asteroid, or dive the cliffs of Miranda… but to do so I’d have to be in freefall, and that — to say the least — doesn’t appeal to me. I have a pretty weak stomach, and I know that being in microgravity* would probably mean me throwing up everything I ever ate ever.

I wish it weren’t true. Weightlessness looks like an awful lot of fun, and it makes everything more interesting. Sleeping, working, everything is different when you’re in freefall.

This was driven home to me when I saw this video put out by the European Space Agency. It came out last year, but I missed it then; happily it’s making the rounds in Facebook again so I stumbled on it. It features one of my favorite astronauts, the Italian spacefarer Sam Cristoforetti, in the International Space Station doing something most of us would take for granted: Making a taco.

It’s way different when you’re making… a SPACE TACO.

That’s so cool! I found it fascinating how, no matter how carefully she places the in-progress taco in front of her to float, it always drifts away. Part of that is due to air currents inside the station, but I suspect some of it is that it’s almost impossible to impart zero momentum to it; no matter how carefully you place it, you’ll always bump it or give it a tiny force, and that will make it move away.

She’s pretty good about capturing runaway food bits, too; catching what looks like a bean at 1:22, though she misses one that escapes a couple of seconds later. I hope she cleaned that up before it caused any problems (which should be fine as long as it isn’t ruffled).

My wife is an excellent cook, and one of my favorite meals she makes is fajitas from scratch. It’s always tempting to put too much filling in them because it’s all so good, but that leads to it plopping out the back end when you bite into it (we have a house rule that when that happens, the other person is within rights to yell out, “Rookie error!”). So I was cringing a bit as Cristoforetti made her taco, thinking it might eject glop into the station when she bit into it. It helped that she folded it in half, and also that she didn’t overstuff it, but still it made me think more about this. In space, the filling could stick farther out the back end of the taco without falling off because there’s no force pulling it down, overcoming its own internal cohesion.

While it does lead to fun physics thought experiments, eating in space is weird. But I guess I’ll never know first hand. Still, I —and my tummy— are OK with that.

* Sometimes you’ll hear people say there’s no gravity in space, but that’s not true; the Earth’s gravity on the astronauts in low Earth orbit is about 90 percent the strength we feel on Earth. But they’re moving around the Earth, moving sideways at the same rate they fall toward the Earth, so they fall continuously without ever hitting. That’s why I prefer the term freefall. “Microgravity” works too because there are still very small forces due to tides and other circumstances, and they really are roughly a millionth as strong as Earth’s gravity. “Zero gravity” is usually a close enough description, if a wee bit imprecise. I discuss all this in my episode of Crash Course Astronomy on gravity:

Categories: Astronomy Headlines

New Study Confirms Sea Surface Temperatures Are Warming Faster than Previously Thought

Thu, 01/05/2017 - 05:45

In 2015, scientists from the National Oceanographic and Atmospheric Administration (NOAA) published a paper that angered a lot of climate science deniers. In it, the researchers found that some historic measurements of sea surface temperatures were off by a bit, and needed to be corrected. Sounds innocuous enough, doesn’t it?

The thing is, when the researchers applied the correction, the so-called global warming “pause” disappeared.  Poof. Gone.

For deniers, this was a red-alert situation. The slow-down in global warming was their go-to cry, their hammer they could wield to claim climate scientists were wrong about warming. If the proposed corrections were real, they lose a big weapon.

Fast forward to yesterday: A new paper published by a different group of researchers studies the same problem in a different way. What they found confirms the suppositions in the earlier paper: Some ocean temperature measurements were indeed off by a bit, and when corrected, show that the hiatus in warming never existed. In fact, the planet has been warming pretty consistently right through the latter half of the 20th century to today.

Deniers will not be happy about this.

The earlier 2015 paper, titled “Possible artifacts of data biases in the recent global surface warming hiatus”, discussed the methods used to measure planetary temperatures, including sea surface temperatures. They found that some older measurements were likely slightly off due to the way they were gathered.

In a nutshell, the problem is that sea surface temperatures are measured in numerous ways. Historically, a big method is to directly sample ocean water using ships. This is problematic, though, because different ships use different methods, and sample water from different depths. Worse, it’s common to measure the water scooped up by intakes that feed it to the engine room to cool the engines. Ships tend to be warmer than the surrounding ocean, of course, so the measurements done this way are biased to be too warm. The ocean water is actually about 0.1°C cooler than what’s measured.

Not only that, but only some ships bring the water in through the engine room. Others throw a bucket over the side and scoop up water. So you have to be careful and adjust for the difference.

When the researchers applied a correction to the data to account for the measurement offset, they found that the rate at which the ocean surfaces were warming was faster than previously determined. When this was combined with data from land and air temperatures, it showed the whole planet was warming faster, too (oceans cover more than 70 percent of the Earth’s surface, and so strongly affect the overall measured temperature).

While it had previously looked like global warming had slowed, this correction shows it hasn’t; when they compared the rate of warming to that in the past few decades, they found it was equal; the warming was occurring at the same rate it had since the second half of the 20th century.

This is the part that, politically, hit like a bomb. For many years, deniers have been claiming that global warming has stopped, or at least drastically slowed, since 1998. This supposed plateau in temperature has been used to make a lot of hay by the anti-science brigade, from fossil fuel funded “think tanks” to fossil fuel funded politicians.

Given that denial is practically a party plank of the GOP, this caused quite a stir.  In reaction to the release of the research showing the pause never happened, Rep. Lamar Smith (R-Texas), chair of the House Committee on Science, Space, and Technology, attacked the NOAA. He started a fishing expedition to try to impede any research they did on climate change, including issuing subpoenas for all emails and data from NOAA scientists, and went as far as accusing scientists of “altering” their data, when really what they were doing was calibrating them, making their data more accurate.

Smith’s McCarthy-esque political shenanigans are ongoing, and will no doubt continue. He’s has shown no signs of abating. And moreover, he’s dead wrong about all this.

The new paper just published will no doubt enflame him. In it, a group of scientists investigated the claims of the earlier paper. They compared the various methods of measuring sea surface temperatures as a way to independently check the historical record. What they found is that the supposition of the first paper was correct: Some measurements were a bit off, and when a correction is applied the global warming slowdown disappears.

Zeke Hausfather, the lead researcher, made a short video explaining what they did:

In the new paper, the researchers looked at newer ways to measure water temperature, including buoys that actually sit in the water, robotic ocean probes called Argo floats, and satellite data. These provide far more accurate data and provide a nice, homogeneous sample.

Isolating these methods and using them to compare to the older data, they found the same bias as found in the earlier paper, confirming them. And when they correct for them, again they find the oceans are warming steadily. The “hiatus” was never real. That’s why I tend to call it the “faux pause”.

This is a very big deal. Remember, Congressperson Smith is accusing NOAA scientists of falsifying data! That is just about the highest crime you can accuse a scientist of doing.

And in fact, the opposite is true: These scientists are trying their damnedest to make sure their work is as accurate as humanly possible. They have devoted their lives to this field of study, and they are critically aware of how important this work is, and what its implications are.

Global warming is one of if not the biggest existential threats to humanity. These new results show that —once again— the overwhelming consensus of climate scientists is right. The planet is heating up. And we also know why: It’s our fault. We burn fossil fuels, adding carbon dioxide to the air, trapping warmth, and heating things up. This is having profound effects on our environment, effects we already see.

Despite this, I expect to hear more denial from Congress, from the incoming President, and from state governments as well. This denial will have a profound effect as well. It’s more than just the appallingly shuttering parts of NASA and the attacks on NOAA. It means years more of inaction toward fixing the problem, and many years more of actively exacerbating it.

There is still hope, though. You can take action. It helps; as we just saw with Congress backing down (for now at least) its gutting of the Office of Congressional Ethics, phone calls work. Make your voice heard.

Categories: Astronomy Headlines

The Snows of… Hawaii?

Wed, 01/04/2017 - 05:45

I’ve been fortunate enough to visit the big island of Hawaii a few times; it’s a fantastically beautiful place and an amazing science destination. There’s a seahorse farm, astronomical observatories, volcanoes, and an eclectic selection of environments, from forbidding lava flows to dry forests to lush tropics.

The edges of the island are at sea level (duh), but the highest point, the peak of Mauna Kea, stretches to 4,200 meters (2.6 miles) above. That brings a lot change in temperature, as you might expect. I watched the sun set from Mauna Kea while I shivered even when wearing a parka; I had gotten used to 35° C humid days.

Still, perhaps the last thing you might expect to see in Hawaii is snow.

But it’s actually pretty common late in the year. The peaks of Mauna Loa and Mauna Kea are high enough that it can stay cold up there, and if moist air gets pushed up the slopes, it’ll condense and fall as snow.

The image above is a lovely example of this. It was taken by the Landsat 8 Earth-observing satellite on Dec. 25, 2016 using the Operational Land Imager camera. It’s natural color, so what you see is pretty much how you’d see it if you were a few hundred kilometers above the volcanic peaks.

I love this shot; the wind was blowing more or less to the west, and you can see streamers of clouds stretching between the two huge volcanoes (Mauna Kea to the north (above) and Mauna Loa to the south (below)) funneled into the saddle between them. The snow on both volcanoes is especially visible because the flanks of both are so barren at high elevation. Driving up the slope of Mauna Kea is like commuting across Mars; it’s a phenomenal vista with reddish-brown lava rocks everywhere.

This is a closer view of Mauna Loa. The central crater (called a caldera) is actually three overlapping craters, collectively called Moku’aweoweo and for scale is about 6.2 km (3.8 miles) along its long dimension. The Sun is shining from the southwest (lower right) so you can see the steep southwest cliff of the caldera by its shadow. I love how the snow tapers off in all directions, feathery and light. The volcano itself actually sports more gentle slopes along its flank than Mauna Kea; its basaltic eruptions tend to be less viscous, so the lava flows more smoothly.

It must be somewhat surreal to stand in a Hawaiian snowstorm (though extremely irritating for astronomers who probably have waited all year to get observations from the world-class observatories on Mauna Kea). Our planet never ceases to amaze me.

By the way, I saw these images at NASA’s fantastic Earth Observatory Image of the Day site, which you should immediately put into your bookmarks/RSS/whateveryouusetogetupdates. Trust me; you’ll not regret it.

Categories: Astronomy Headlines

Seeing Through a Cloudy Lens

Tue, 01/03/2017 - 05:45

Going through old emails is like a treasure hunt sometimes. I found a gorgeous photo of a spiral galaxy recently, and then saw an email from photographer Brad Goldpaint about another type of object of my affection: lenticular clouds.

These are lens-shaped clouds sculpted by winds, usually found over mountains. The rising air can create standing waves, stationary up-and-down oscillations, downwind. The first crest, just downwind of the mountain, can form a cloud as the air rises and cools. The moisture in the cloud is swept downstream but is replaced by more air rising … and you get a stationary cloud, lens-shaped due to the flowing wind, that seems to hover near the mountain peak.

It’s no surprise people think these are UFOs sometimes. They’re honestly pretty amazing.

The photo above shows a magnificent example over Mount Shasta, which Goldpaint took in 2015. It shows the lenticular clouds lit by the Moon in the evening. As cool as that photo is, I like the one he took a bit earlier even better, when the clouds over Shasta were lit by the setting Sun.

Holy wow! That smooth cloud over the mountain is an indication of laminar flow, smoothly moving air. I love how it follows the contour of the mountains.

Goldpaint also made a short time-lapse video showing how the clouds are stationary even as the air moves:

How cool is that?

I spot lenticular clouds pretty often, seeing as how I live near the foothills of the Rocky Mountains. I saw some just the other day, in fact:

As I said when I posted this shot on Instagram, “Goats and lenticular clouds. Maybe the first time those words have ever been used together.”

If you like Goldpaint’s work, then check out his gallery. And if you want more lenticulars, I have links to some other spectacular shots below. Enjoy.

Categories: Astronomy Headlines

Deep Field

Mon, 01/02/2017 - 05:45

The Universe is cycles.

Planets orbit their stars. Stars are born and die and seed the Universe with more gas and elements to create more stars. Galaxies spin. Closer to home, we see the Sun rising and setting, we awake and we sleep. Even the sounds we hear are cycles; musical chords are juxtaposed oscillations at specific frequencies, compression and rarefaction of air.

And here we are, at the beginning of a new, if somewhat arbitrary, cycle. With a fresh orbit around the Sun lying ahead of us, I want to show you something to think about in the coming year.

The image at the top of this article is called the Hubble Deep Field. It was the first of several subsequent projects using the venerable observatory to stare at a single patch of sky for days, weeks, building up an image of some the faintest objects ever seen. When it was first undertaken, we weren’t sure what we were going to find.

When the observations were processed and assembled, what we found was awe.

Nearly every object in that image is a galaxy, a vast, sprawling complex of gas, dust, and stars. Thousands were revealed in the image, despite the field of view being so tiny. If you held a grain of sand on your finger, your arm outstretched, it would occupy as much of the sky as the Deep Field does.

And yet, what lies inside those boundaries is the Universe itself.

This profundity inspires us. It did so to Eric Whitacre, a composer and conductor of classical music. He was moved to write an orchestral piece called “Deep Field”, and it’s a paean to this mesmerizing image of space. The piece is about 20 minutes long, and I urge you to sit, relax, and listen to the whole thing:

Another version by the Bel Canto Choir Vilnius is available, too.

The piece mirrors the observation in many ways, metaphorically and literally.

It seems to be made of several themes, somewhat disjointed, that come together to form a greater whole, rising to a stirring climax. But note the image itself! In it, we see that the most distant galaxies —the ones we see when the Universe was young— are smaller, less well defined. We know that these galaxy fragments in the early Universe came together under their mutual gravity, merging to form the glorious, far larger and more well organized galaxies in the modern Universe.

Some of the music sections are dissonant, with conflicting chords, resolving themselves after a moment, or repeated with slightly different component notes to resolve them. I rather like that; it reminds me of seeing apparently overlapping galaxies in the image that become clear when zoomed in, or simply become easier to distinguish. And part of the point of the Hubble observation was to use its superior eyesight —what astronomers actually call resolution!— to distinguish all the objects in the field.

Two different meanings for the word, yet both come together where music and science meet.

Toward the end, the choral part starts, wordless voices in gorgeous, lush harmony with the orchestra. The tone of the whole work changes, but in a very organic, natural way, uplifting and hopeful yet retaining its pensive, even reverent attitude. It reminds me of the ending of Holst’s suite “The Planets”, where voices fade out at the end of “Neptune”, as if we are being borne away from the solar system, the Sun and its attendant planets receding and fading as we move away into the black.

If you want comments from the composer himself, Whitacre recorded a short video describing the piece (starting about one minute in) :

The idea of using the audience phones is clever. Besides adding to the sound of the music, from the orchestra’s view they see dozens, hundreds of small lights scattered around them out in the black hall, mimicking the galaxies in the Deep Field itself. What a lovely idea.

I have listened to this piece of music many times now, and I must muse on its origin. These galaxies, these distant structures that dwarf us and crush our sense of space and time… they do not care about us. They are things, not alive, not sentient, incapable of feeling or purpose. And yet they are us. The galactic fragments and even full-fledged galaxies in the Hubble Deep Field are representative of the same cosmic constructs that formed the Milky Way, the first and second generation of stars in it, the supernovae and heavy elements that settled into swirling disks of material that birthed our Sun, our planet.

We evolved here, on this spinning planet, we grew from abiotic material to life, became complex, and eventually, after billions of years, became us. You. Me. Our sense of beauty and wonder and curiosity turned our gaze to the sky and allowed us to discover the pieces of Universe that were our origins, looking back across countless light years to how we came to be.

This in turn inspires art, prose and music, a unique outlook and perspective on nature that we can share and appreciate. The science created the art, and the art informs the science. Perhaps one could exist without the other. Perhaps. But together they are more than either individually or summed. Together they are the very basis of what it means to be human, the joy of understanding and expressing that humanity.

Which brings us back to cycles, and back to how this article started. Which is to say…

Happy new year. There will always be new years, but never quite this one again. Do what you can to make it a good one.

My thanks to astronomer, astronomy communicator, and friend Kim Kowal Arcand for the link to this wonderful piece of music.

Categories: Astronomy Headlines

Happy New Tropical Earth Orbital Period! Kinda!

Sun, 01/01/2017 - 05:30

Another year, another repost: The article below is an updated version of one I try to post every year at this time — either because the topic is so much fun, or I'm lazy. Take your pick. But I love this kind of stuff; it's fun to research and to play with the numbers. If you like it too, read on. If you don't, read it anyway, because you might find out you do, and isn't that one reason we celebrate the new year? To try out and experience new things, or old things anew? You might also want to read about why we have leap years and even leap seconds. Science! I love this stuff.

Yay! It’s a new year!

But what does that mean, exactly?

The year, of course, is the time it takes for the Earth to go around the Sun, right? Well, not exactly. It depends on what you mean by “year” and how you measure it. This takes a wee bit of explaining, so if you're done kicking 2016 to the curb and trying your best to hope for 2017, sit back and let me tell you why we have a new year at all.

Round and Round She Goes

Let’s take a look at the Earth from a distance. From our imaginary point in space, we look down and see the Earth and the Sun. The Earth is moving, orbiting the Sun. Of course it is, you think to yourself (unless you're a Geocentrist, in which case this stuff still all works, just the other way around). But how do you measure that? For something to be moving, it has to be moving relative to something else. What can we use as a yardstick against which to measure the Earth’s motion?

Well, we might notice as we float in space that we are surrounded by billions of pretty stars. We can use them! So we mark the position of the Earth and Sun using the stars as benchmarks, and then watch and wait. Some time later, the Earth has moved in a big circle (OK, ellipse, but they're pretty close in this case) and is back to where it started in reference to those stars. That’s called a “sidereal year” (sidus is the Latin word for star). How long did that take?

Let’s say we used a stopwatch to measure the elapsed time. You'll find that it took the Earth 31,558,149 seconds (some people like to approximate that as pi x 10 million = 31,415,926 seconds, which is an easy way to be pretty dang close—better than a half a percent accuracy). That's an inconvenient number of seconds, though. I think we'd all prefer to use days instead. So how many days is that?

Well, that’s a second complication. A “day” is how long it takes the Earth to rotate once, but we’re back to that measurement problem again. But hey, we used the stars once, so let’s do it again! You stand on the Earth and define a day as the time it takes for a star to go from directly overhead to directly overhead again: a sidereal day. That takes 23 hours 56 minutes 4 seconds = 86,164 seconds. But wait a second (a sidereal second?)—shouldn’t that be exactly equal to 24 hours? What happened to those 3 minutes and 56 seconds?

I was afraid you’d ask that—but this turns out to be important.

It’s because the 24-hour day is based on the motion of the Sun in the sky, and not the stars. During the course of that almost-but-not-quite 24 hours, the Earth was busily orbiting the Sun, so it moved a little bit of the way around its orbit (about a degree). If you measure the time it takes the Sun to go around the sky once—a solar day—that takes 24 hours, or 86,400 seconds. It’s longer than a sidereal day because the Earth has moved a bit around the Sun during that day, and it takes a few extra minutes for the Earth to spin a little bit more to “catch up” to the Sun’s position in the sky.

A diagram from Nick Strobel’s fine site Astronomy Notes (shown here; click to embiggen) helps explain this. See how the Earth has to spin a little bit longer to get the Sun in the same part of the sky? That extra 3 minutes and 56 seconds is the difference between a solar and sidereal day.

OK, so we have a year of 31,558,149 seconds. If we divide that by 86,164 seconds/day we get 366.256 days per year.

Wait, that doesn’t sound right. You’ve always read it’s 365.25 days per year, right? But that first number, 366.256, is a year in sidereal days. In solar days, you divide the seconds in a year by 86,400 to get 365.256 days.

Phew! That number sounds right. But really, both numbers are right. It just depends on what unit you use. It’s like saying something is 1 inch long, and it’s also 2.54 centimeters long. Both are correct.

Having said all that, I have to admit that the 365.25 number is not really correct. It’s a cheat. That’s really using a mean or average solar day. The Sun is not a point source, it’s a disk, so you have to measure a solar day using the center of the Sun, correcting for the differences in Earth’s motion as it orbits the Sun (because it’s not really a circle, it’s an ellipse) and and and. In the end, the solar day is really just an average version of the day, because the actual length of the day changes every, um, day.

The Sun Rose by Any Other Name

Confused yet? Yeah, me too. It’s hard to keep all this straight. But back to the year: That year we measured was a sidereal year. It turns out that’s not the only way to measure a year.

You could, for example, measure it from the exact moment of the March equinox (also northernhemispherictically sometimes called the vernal equinox) —a specific time of the year when the Sun crosses directly over the Earth’s equator in March— in one year to that same equinoctal moment in the next. That’s called a tropical year (which is 31,556,941 seconds long). But why the heck would you want to use that? Ah, because of an interesting problem! Here’s a hint:

The Earth precesses! That means as it spins, it wobbles very slightly, like a top does as it slows down. The Earth’s wobble means the direction the Earth’s axis points in the sky changes over time. It makes a big circle, taking over 20,000 years to complete one wobble. Right now, the Earth’s axis points pretty close to the star Polaris, but in a few hundred years it’ll be noticeably off from Polaris.

Remember too, that our seasons depend on the Earth’s tilt. Because of this slow wobble, the tropical year (from season to season) does not precisely match the sidereal year (using stars). The tropical year is a wee bit shorter, by 21 minutes or so. If we didn’t account for this, then every year the seasons would come 21 minutes earlier. Eventually we’ll have winter in August, and summer in December! That’s fine if you’re in Australia, but in the Northern Hemisphere this would cause panic, rioting, people leaving comments in all caps, and so on.

So how do you account for this difference and not let the time of the seasons wander all over the calendar? Easy: You adopt the tropical year as your standard year. Done! You have to pick some way to measure a year, so why not the one that keeps the seasons more or less where they are now? This means that the apparent times of the rising and setting of stars changes over time, but really, astronomers are the only ones who care about that, and, not to self-aggrandize too much, they’re a smart bunch. They know how to compensate.

OK, so where were we? Oh yeah—our standard year (also called a Gregorian year) is the tropical year, and it’s made up of 365.25 mean solar days (most of the time, actually), each of which is 86,400 seconds long, pretty much just as you’ve always been taught. And this way, the March equinox always happens on or around March 21 every year.

Lend Me Your Year

But there are other “years,” too. The Earth orbits the Sun in an ellipse, remember. When it’s closest to the Sun we call that perihelion (the farthest point is called aphelion). If you measure the year from perihelion to perihelion (called an anomalistic year, an old term used to describe the shape of an orbit) you get yet a different number! That’s because the orientation of the Earth’s orbital ellipse changes due to the tugs of gravity from the other planets, taking about 100,000 years for the ellipse to rotate once relative to the stars. Also, it’s not a smooth effect, since the positions of the planets change, sometimes tugging on us harder, sometimes not as hard. The average length of the anomalistic year is 31,558,432 seconds, or 365.26 days. What is that in sidereal days, you may ask? The answer is: I don’t really care. Do the math yourself.

Let’s see, what else? Well, there’s a pile of years based on the Moon, too, and the Sun’s position relative to it. There are ideal years, using pure math with simplified inputs (like a massless planet with no other planets in the solar system prodding it). There’s also the Julian year, which is an ideally defined year of 365.25 days (those would be the 86,400 seconds-long solar days). Astronomers actually use this because it makes it easier to calculate the times between two events separated by many years. I used them in my Ph.D. research because I was watching an object fade away over several years, and it made life a lot easier. Doctoral research is hard, shockingly, so you learn to take advantages where you can find them. 

Where to Start?

One more thing. We have all these different years and decided to adopt the tropical year for our calendars, which is all well and good. But here’s an issue: Where do we start it?

After all, the Earth’s orbit is an ellipse with no start or finish. It just keeps on keeping on. But there are some points in the orbit that are special, and we could use them. For example, as I mentioned above, we could use perihelion, when the Earth is closest to the Sun, or the vernal equinox. Those are actual physical events that have a well-defined meaning and time.

The problem, though, is that the calendar year doesn’t line up with them well. The date of perihelion changes year to year due to several factors (including, of all things, the Moon, and the fact that we have to add a leap day roughly every four years). In 2013 perihelion was on Jan. 2, but in 2017 it’s on Jan. 4. Same thing with the equinox: It can range from March 20 to March 21. That makes using orbital markers a tough standard.

Various countries used different dates for the beginning of the year. Some had already used Jan. 1 by the time the Gregorian (tropical) calendar was first decreed in 1582, but it took time for others to move to that date. England didn’t until 1752 when it passed the Calendar Act. Not surprisingly, there was a lot of religious influence on when to start the new year; for a long time a lot of countries used March 25 as the start of the new year, calling it Lady Day, based on the assumed date when the archangel Gabriel told Mary she would be the mother of God. Given that a lot of ancient Christian holidays are actually based on older, Pagan holiday dates, and the fact that this was on March 25—very close to the equinox—makes this date at the very least suspicious.

Still, in the end, the date to start the new year is an arbitrary choice, and Jan. 1 is as good a day as any. And as a happy side effect it does help establish the Knuckle Rule.

Resolving the New Year

So there you go. As usual, astronomers have taken a simple concept like “years” and turned it into a horrifying nightmare of nerdery and math. But really, it’s not like we made all this stuff up. The fault literally lies in the stars and not ourselves.

Now if you’re still curious about all this even after reading my lengthy oratory, and you want to know more about some of these less well-known years, then check out Wikipedia. It has lots of info, but curiously I found it rather incomplete. Every year (take your pick which kind) I say to myself I'll submit an updated article to Wikipedia listing all the different years and the number of seconds and days of each kind in them. 

Then every year I forget. But if you want to give it a shot, feel free. It would come in handy when I update this article every 365.26 days or so.

Incidentally, after all this talk of durations and lengths, you might be curious to know just when the Earth reaches perihelion, or when the exact moment of the vernal equinox occurs. If you do, check out the U.S. Naval Observatory website. It has tons of gory details about this stuff.

And, finally (for real this time) I have to add one more bit of geekiness. While originally researching all this, I learned a new word! It’s nychthemeron, which is the complete cycle of day and night. You and I, in general, would call this a “day.” Personally, if someone dropped that word into casual conversation, I’d challenge them to a duel with orreries at dawn.

Hmmmm, is there anything else to say here? (Counting on fingers.) Years, days, seconds, yeah, got those. (Mumbling.) Nychthemeron, yeah, Gregorian, tropical, precession, anomalistic … oh wait! I know something I forgot to say:

Happy New Year! 

Categories: Astronomy Headlines

2017: Wait Just a Second

Fri, 12/30/2016 - 05:45

If, like me, you’re counting the seconds until you can kick 2016 out the door, I have a tiny bit of bad news: You’ll have to count a little higher to do so. According to our clocks, 2016 will be exactly one second longer this year because scientists are adding a leap second to it.

Leap seconds are added to the calendar pretty often, actually, on average a little less than one every year [Note: Leap seconds are wholly different than leap years, which come with their own set of mathematical funness]. This is done to keep our clocks in sync with the rotating Earth.

Basically, we have lots of ways of measuring time. One is to very carefully measure how long it takes the Earth to spin once on its axis. We call that a “day”. There are actually lots of different kinds of days — how long it takes the Earth to spin once relative to the Sun, or relative to the average position of the Sun in the sky, or relative to the stars. But all of these are based on the spinning Earth.

That was fine for pre-electronic technology, but nowadays we need something better. The Earth makes a pretty ratty clock when you focus in on very tiny timescales. Lots of forces affect our planet’s spin, including the tides from the Sun and Moon, continental drift, and even the way we dam up rivers. The overall change is pretty small: The length of our day now is only about two milliseconds longer than it was around 1820, which is when there were exactly 86,400 standard seconds in a day.

So yeah, our day is now 86,400.002 seconds. Give or take. I know that doesn’t sound like much, but it adds up. What it means is that the Earth spins a touch slower now, and doesn’t keep time as well as the atomic clock does. So, every now and again, we have to correct for it.

I described this in an article about leap seconds from 2008:

Imagine you have two clocks. One thinks there are 86,400 seconds in a day, the other thinks that there are 86,401, so the second clock runs a tad bit slower than the first. Every day, it's one second behind, clicking over to midnight one second after the first clock does. Mind you, it keeps accurate time according to its own gears: every day has 86,401 seconds, so it's not slowing down. However, to keep it synchronized with the other clock, we'd either have to subtract a second from the second clock (yikes, terminology is a bit confusing there!) or add one to the first clock every day. So we'd need a leap second every day, but not because the clock is slowing. It's only because it runs at a different (but constant) rate.

This is the part that confuses people. It’s not really that the Earth is spinning slower all the time, it’s just that right now it’s spinning slower than it did a while back. Even if the Earth’s rotation were perfectly constant now, we’d still have to add a leap second! I’ll note that some young-Earth creationists use this slowing to argue the Earth can’t be old, but, unsurprisingly, they’re wrong about this.

Anyway, we now use atomic clocks to keep standard time independent of our planet’s spin. They’re based on the frequency of an electron transition in cesium atoms —yes, seriously, and if you want details here they are. But this method is far more accurate, and can easily measure the time difference due to the slowpoke Earth.

When the difference between the atomic clocks and the Earth clocks differ by more than 0.9 seconds, a leap second is added to civil time (the time used by civilian authorities*). It could technically be subtracted if the Earth’s rotation were to speed up, but that’s never been the case since this method was adopted.

In fact we’ve been adjusting our clocks this way since 1972. In the 34 years since then, we’ve added 26 leap seconds to the calendar. The last one was in June, 2015.

But this year’s end will see another next leap second. What does this mean?

On Saturday night, Dec. 31st, 2016, at 23:59:59, one second will be added to our clocks. Instead of clicking over to Jan. 1, 2017 at 00:00:00, for one second the official time clock will instead read 23:59:60.

I know, right? Weird. But if we didn’t do this, all our computer clocks and everything else would get seriously messed up. Timekeeping is a serious business.

This probably won’t affect you in any way personally, unless you succumb to any existential dread of having this year be 0.000003169 percent longer. That’s been true of nearly every year for decades anyway.

And think of it this way: The motions of heavenly bodies affect us in ways you may not realize. I don’t mean astrologically, of course; that’s just hogwash. Obviously: Even the Sun and Moon can only change the Earth’s rotation by a wee bit over centuries, so their affect on you is even, um, weeer.

For me, this just reinforces my love of astronomy and science. After all, our human senses only perceive a tiny fraction of what’s going on around us, and our affairs are a minor thing compared to the Universe around us. I think that helps me keep a certain perspective; despite what happens on it, the Earth itself keeps on turning. Perhaps a scosh more slowly, but if that’s the price to pay to go along for the ride on this rotating ball of rock and water and metals careening through the cosmos, I think it’s an affordable one.

* Not to be confused with the time to be civil, which is nearly all the time.

Categories: Astronomy Headlines

Amazing Illusion: Invisibility Cloak

Thu, 12/29/2016 - 05:45

My friend (and evil twin) Richard Wiseman is a staple here at BA HQ; he studies how our brains can be tricked into perceiving things that aren’t real … or missing things that really are there.

His latest entry into encephallusions* is masterful. Almost a century ago, the brilliant magician Robert Harbin came up with a way to seemingly cloak someone, as if part of them were to become invisible. It’s never been done in practice … until now. Richard—with a little help—made it real, and put together a wonderful video demonstrating it.

What do you think? How does this work? First, try to guess …

If you’re the kind of person who can’t stand not knowing—and good for you, that’s a big step in looking at the world scientifically!—then Richard made a second video explaining it:

Did you guess correctly? I did, kinda; I knew it had to do with reflections and angles, though I didn’t go to the trouble of doing the actual ray tracing (that is, figuring out the direction the light traveled). It’s very clever, and like a good showman Richard really sells it by moving his arm behind the ninja, making it look like she really is cloaked.

But there’s something he doesn’t explain in the video, and since it’s science, I will. Did you see him drop the bead in the bowl of water only to have it disappear? How does that work?

It has to do with refraction, the bending of light. When light travels from one medium (say, air) to another (say, water) at an angle it bends a little bit, changing the direction it travels. It’s actually changing its speed, and the amount of change depends on the material through which light is traveling. The amount by which the material can change the light’s speed (and the angle at which it bends) is called the index of refraction. It’s just a number that falls out of the equations, and, for example, water has an index of refraction of about 1.33.

You’ve seen this lots of times; it’s why a spoon looks bent when you stick it in a glass of water (it also distorts the Sun, Moon, and stars when they set as their light passes through our atmosphere). If you put something transparent in water, though, things can get weirder. If that object has a different index, the light passing through the water bends a little when it passes through that object, distorting the view. Usually, this makes it a bit easier to see the object because you can see its edges better where the light is distorted.

But if the object has an index of refraction equal to that of water, the light passes right through it without distortion, and the object seems to disappear! The glass beads Richard used in the video have the same index as water, so when he dropped them in they disappeared from view.

This can be done with Pyrex and glycerine, for example, and many other pairs of transparent objects. It’s a very different effect than what Richard shows in the cloaking illusion, but in the end they both fall under the same category of “making stuff appear to disappear.”

Science! Ain’t it grand? And it’s useful: It can really help you understand when you’re being fooled, whether it’s just your brain not perceiving things the way they should be, or because someone is trying to fool you. But either way, it’s your best bet.

* Yes I just made that word up. I do that sometimes.

Categories: Astronomy Headlines