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Students Discover a Galactic Eye of Horus

5 hours 21 sec ago

Undergraduate students in Japan stumbled upon a rare lensing of two distinct background galaxies.

Eye of Horus in pseudo color. Enlarged image to the right. The yellow object at the center is a galaxy about 7 billion light-years away and bends the light from two background galaxies.   NAOJ

Eye of Horus in pseudo color. Enlarged image to the right. The yellow object at the center is a galaxy about 7 billion light-years away and bends the light from two background galaxies.

I don’t know about you, but I’ve always secretly wanted to serendipitously discover something incredible in one of my lab courses. Well, some students in Japan got to experience just that. A group of astronomers and undergraduate students at the National Astronomical Observatory of Japan (NAOJ) in Tokyo found a unique galaxy system they dubbed the Eye of Horus.

Masayuki Tanaka (NAOJ) and several students were looking at images from the Hyper Suprime-Cam (HSC) taken at the Subaru telescope. Student Arsha Dezuka expressed her surprise at finding the odd-looking system.

Once Tanaka saw the warped light, he immediately recognized it as a strong gravitational lens — where the gravity of a galaxy bends the light from a galaxy behind it. Strong lensing helps probethe distribution of matter around galaxies.

A closer look at the images showed one reddish ring and another with a blue tint. The two colors suggested that not just one, but two galaxies were being lensed, something that’s rarely observed. There are only a handful of systems like this currently known, but the distance galaxies haven’t been measured because they’re too faint.

Based on data from the Sloan Digital Sky Survey, light from the lensing galaxy takes 7 billion years to arrive at Earth. Astronomers conducted follow-up observations on the Magellan Telescope and confirmed that light from the background galaxies take 9 and 10.5 billion years, respectively. The data not only confirm that there are two galaxies at two different distances, but one of the galaxies seems to be made of two distinct clumps, according to Kenneth Wong (NAOJ). This could be due interacting

With 300 nights of data, the HSC survey is the largest observing program ever approved at the Subaru Telescope. The survey, still in its early phases, hopes to address outstanding astrophysics questions about dark energy, galaxy evolution, and when galaxies first started pumping out stars. The team expects to find about 10 more double-lensed galaxies in the survey.

The paper on the discovery was published in the July issue of Astrophysical Journal Letters.

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Categories: Astronomy Headlines

Delta Aquarids Kick Off Summer Meteor Showers

Wed, 07/27/2016 - 06:41

The meteors are coming! Three annual meteor showers are already active and guaranteed to spark up your summer nights. 

Delta Aquarids

The Delta Aquarid meteor shower peaks this week. This view shows the sky around 1:00 a.m. local time.  All the meteors appear to streak away from a spot called the radiant, which lies about 10° above the bright star Fomalhaut and near the fainter star Delta (δ) Aquarii — hence the shower's name.

Open the gate. Here they come! It's time for the annual trifecta of late July-early August meteor showers beginning with the Delta Aquarids which peak the night of July 28-29. The last meteor shower of note occurred in early May when the Eta Aquarids sprinkled a modest few meteors across the dawn sky. Yes, it's been a long time.

The Delta Aquarid meteor shower takes its name from Delta Aquarii, a third magnitude star in the constellation Aquarius, the Water Carrier. Shower meteors fan out across the sky, but all appear to streak away from a point in central Aquarius called the radiant.

A sure way to know if you've spotted a Delta Aquarid is to trace its path backwards. If it returns you to the vicinity of Delta Aquarii, you've got a keeper.

Matter of Perspective

Car headlights reveal a dazzling "snow radiant", a perspective effect much the way meteors appear to radiate from a point in the sky during a meteor shower. In the case of snow, the car is moving into the storm. With meteors, Earth is zipping along its orbit while traveling through debris deposited by comets and sometimes asteroids.
Bob King

The radiant is a perspective effect caused by meteors arriving from the same direction at similar speeds. If you've ever driven through a heavy rain or snowstorm at night, you've probably noticed that precipitation caught in your headlight beams appears to "radiate" from a point in the distance. The illusion is identical to the that of railroad tracks converging in the distance. Still, despite appearances, we know the tracks remain parallel just the way meteors do when they spear through the atmosphere.

Some meteor showers have sharp peaks, others are "soft", with broadly spread-out activity. The Delta Aquarids typically fire off 15 to 20 meteors per hour before dawn begins, when Aquarius is highest in the sky — its broad peak is centered on Friday morning. Since most shower members are rather faint, plan to catch the show from a reasonably dark sky.

What's nice about these more diffuse showers is that they keep putting out meteors a week or more before and after maximum. If the weather doesn't cooperate one night, you can look the next. Or the next.

Explosive Arrival

A bright Delta Aquarid flares during its plunge through the atmosphere.
Jimmy Westlake

You can start watching as "early" as midnight when Aquarius pokes its head up in the southeastern sky, but 2 a.m. local time might be better since that's when the radiant crosses the meridian and stands highest in the south at 3:15 a.m.. Dawn begins around 4 a.m. for observers at mid-northern latitudes.

Because the radiant is relatively low in the southern sky, skywatchers in tropical and southern latitudes will see more meteors than those farther north. Why? Meteors that flash a significant distance south of the radiant get cut off by the southern horizon.

Whatever time you choose to begin your vigil, find a location with a minimum of light pollution and set up a comfy reclining lawn chair facing east or south for the best view. Remember to bring a blanket to ward off the damp chill of a humid night. Coffee and tea are welcome and even a little music for atmosphere. Or you can soak in the soft stridulations of crickets and katydids.

The Moon hugely affects how many meteors you might see. Lucky for meteor lovers, it will be a 23% waning crescent considerably farther east in Taurus on Friday morning and should make only a small dent in meteor counts.

Aldebaran Occultation Friday Morning Double Feature

This map shows the crescent Moon gliding just south of Aldebaran as viewed from the central U.S. around 5 a.m. local time July 29.

But hold on — the Moon has it's own agenda. That very same morning, it will either just miss or occult the bright star Aldebaran shortly after 10:00 UT (5 a.m. CDT).

If you live south of a line that crosses from Toledo, Ohio through St. Louis, Missouri; Tulsa, New Mexico; and El Paso, Texas, the Moon will cover the star. North of the line, it will glide just beneath it. Fortunate observers living within a half-mile either side of the line will witness a spectacular grazing occultation as Aldebaran repeatedly disappears and reappears behind the Moon's north polar peaks. Rarely has there been a better incentive to get up early for a meteor shower! Check here for full details.

The Origin of the Delta Aquarids Deltas' Daddy

Comet 96P/Machholz photographed by the STEREO-A spacecraft. It's the possible parent comet of the annual Delta Aquarid meteor shower.

Each Delta Aquarid that flashes into view represents a crumb of debris sloughed off by comet 96P/Machholz discovered in 1986 by American amateur astronomer Don Machholz. Solar heating vaporizes ice and loosens dust and small rocks from the comet. Some of the material falls back and coats the surface, and some gets pushed away by sunlight to form a trail of debris in the comet's wake. Every July, Earth sprints through 96P's trail; as the material strikes the atmosphere at 93,000 miles per hour (42 km/sec) and vaporizes, we get treated to glittery streaks of light.

The Capricornids

The Alpha Capricornids, which originate from Comet 169P/NEAT, are active at the same time as the Delta Aquarids and radiate from northwestern Capricornus. They stand out for being unusually slow-moving and often bright. You may see five of these per hour in the last week of July under ideal conditions radiating from the northwestern corner of Capricornus. But in the far future, this shower should become intense!

Meteor-stream calculators Peter Jenniskens and Jérémie Vaubaillon find that only the outer fringe of the stream currently crosses Earth’s orbit, and that the stream should have a rich inner core. This core should start intersecting Earth’s path in the 24th century. They predict that the Alpha Capricornids will be a major sky event every year from about 2200 to 2400 A.D., “stronger than any current shower,” according to S&T Senior Editor Alan MacRobert.

Perseid Meteor Shower Completes the Trifecta

Earlier I mentioned a trifecta of meteor showers. You can probably guess the third offering — the Perseids! Although the shower peaks on the night of August 12-13 with numbers in the neighborhood of 100 per hour, it's been active since mid-July, so don't be surprised if an outing over the next few nights nets a few Perseids, too.

The radiant of the Perseid Meteor Shower is high in the sky by 11 p.m. for observers at mid-northern latitudes.

The radiant of the Perseid meteor shower is high in the sky by 11 p.m. for observers at mid-northern latitudes. Although the Moon will interfere early on August 12-13,  it sets around 1:30 a.m. leaving dark skies till dawn.
Sky & Telescope

On the night the shower peaks, the Moon will be two days past first quarter in Ophiuchus and compromise the view a bit until it sets around 1:30 a.m. From then till dawn, we're likely to see the shower at its best.

Perseids originate from 109P/Swift-Tuttle and slash the sky with their swiftness. Fireballs as well as meteors leaving persistent, smoke-like trains are common.

Keeps On Going and Going and ...

My camera captured only a short portion of a Leonid earthgrazer's flight across more than half the sky in November 2009. The radiant was still below the horizon at the time. The Pleiades star cluster is seen at lower left. 
Bob King

With all three showers, keep an eye out for earthgrazers, meteoroids that arrive at Earth at a very low angle. Instead of following a more typical, steeply-slanted path downward, they skim the upper air, often taking many seconds to finally fizzle out. Earthgrazers are more common when a shower’s radiant is either just below or a short distance above the horizon.

Let the fireworks begin!

Make the most of the Perseid meteor shower when you download our FREE ebook, Shooting Stars: The Science, Art, and History of the Perseids, and as a bonus you'll also receive our weekly e-newsletter with the latest astronomy news.

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Categories: Astronomy Headlines

NASA’s K2 Mission Confirms 100+ Exoplanets

Wed, 07/27/2016 - 06:40

Kepler’s K2 mission has confirmed 104 new exoplanets — including a rocky, four-planet system.

An artist’s concept of the four rocky planets near M dwarf star K2-72 discovered by K2. Two of these are in the “habitable zone”, where liquid water may be present on the surface.   NASA / JPL

An artist’s concept of the four rocky planets near M dwarf star K2-72 discovered by K2. Two of these are in the “habitable zone”, where liquid water may be present on the surface.

In 2009, NASA launched Kepler with the intention of searching for Earth-sized planets orbiting stars similar to the Sun. In 2014, the aging telescope entered a second life, searching for exoplanets across a broader swath of sky. Of 197 planet candidates, scientists have now confirmed 104 planets that range between 20% and 50% times larger than Earth’s diameter.

Crossfield and colleges confirmed the large number of exoplanets by combining Kepler data with follow-up observations from groundbased telescopes such as the North Gemini telescope and the Keck Observatory. The discoveries were published online in the Astrophysical Journal Supplement Series.

Detecting Exoplanets

Kepler discovers transiting planets — those that pass in front of their star and subtly dim its brightness. Over its four-year survey, Kepler surveyed one patch of the sky in the northern hemisphere. During that time, it found  4,696 candidate exoplanets — 2,329 of these were confirmed as of July 18, 2016.

K2 is an extension of the Kepler missionthat covers more of the sky, albeit with lower pointing accuracy. This has allowed it to observe a larger fraction of cooler, smaller, and often nearby red dwarf stars, which are much more common in the Milky Way than Sun-like stars. To date, the K2 mission has found 458 candidate planets, 127 of which have been confirmed. The general scientific community proposes all K2 targets.

"An analogy would be to say that Kepler performed a demographic study, while the K2 mission focuses on the bright and nearby stars with different types of planets," says Ian Crossfield (University of Arizona) in a press release.

Among the confirmed planets is a four-planet, potentially rocky, system orbiting the M dwarf star K2-72 181 light-years away in Aquarius. These planets have periods ranging from 5.5 to 24 days and despite their smaller-than-Mercury orbits, the possibility that life could exist on a planet around such a star cannot be ruled out, according to Crossfield.

In addition to finding planet candidates, K2 has already revealed oscillations in variable stars and discovered eclipsing binaries and supernovae. Astronomers expect K2 will discover between 500 and 1,000 planets in its planned three- to four-year mission.

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Categories: Astronomy Headlines

Missing Craters on Ceres

Tue, 07/26/2016 - 13:38

The dwarf planet has a paucity of big pockmarks because it has somehow erased them.

Ceres and its plain

Shown north down in this false-color image, Ceres has many craters, but few large ones. Its largest is Kerwan (280 km wide), the rims (red-yellow) and central depression (blue) of which are clear in this topographic map. Beneath Kerwan hides an 800-km-wide, 4-km-deep depression (in green) called Vendimia Planitia. This depression is possibly what’s left of one of the largest craters from Ceres’s earliest collisional history.

Simone Marchi / SWRI

Ceres is the largest body in the asteroid belt. It spans about 940 km (580 miles), more than half again as big as one of the next largest asteroids, Vesta (525 km/326 mi). Over the course of the solar system’s 4½ billion years, these bodies have received an almighty pummeling from rocks and comets, leaving their surfaces battle-scarred.

But, as Simone Marchi (Southwest Research Institute) and others report July 26th in Nature Communications, when it comes to big craters Ceres is strangely smooth.

Vesta, which NASA’s Dawn spacecraft visited before it arrived at Ceres in 2015, has a devastated-looking surface. Its largest crater (Rheasilvia) is nearly as wide as the asteroid itself. Planetary scientists estimated that Ceres would also look ragged, with roughly a dozen craters bigger than 400 km. Yet its largest crater, Kerwan, spans only 280 km. And of the 40-plus pockmarks the dwarf planet “should” have that are larger than 100 kilometers, it has only 16.

Ceres does, however, have a bunch of smaller craters — so many that in some areas the surface is saturated with them, meaning that for every new crater created, another one is erased. These could hide older, larger structures.

And in fact the team has now found the echo of an 800-km-wide crater: the low-lying Vendimia Planitia, hidden to the eye but apparent (barely) in a topographic map. Kerwan lies within its southern edge. The putative basin also looks distinctly different in terms of chemical makeup than the rest of Ceres, suggesting the impact might have excavated stuff with a different composition or triggered its creation when the body hit.

Even with that finding, though, there still aren’t enough large craters to satisfy scientists — it’s very difficult to explain why there are so few in the 100- to 400-km range.

The solution is that Ceres has likely erased its scars with time. This process could have happened a couple of ways. Recent analysis by the Dawn team suggests the dwarf planet’s subsurface is 30% to 40% ice by volume. Without a rigid rock makeup, Ceres’s surface would relax over time, like skin does after you press it hard with your fingertip. This relaxation would slowly obliterate craters. And since big craters happened more often in the solar system’s early history — when more big hunks of rock were flying around — those would be more faded relative to smaller ones.

Another possibility is that ice volcanism resurfaced Ceres. The infamous bright spots in the crater Occator and elsewhere are salt deposits, and they may have been left there by water rising from below and then evaporating away. If so, then this world was geologically active (maybe it still is?) and could have remade its façade.


You can read more about the results in the press releases from JPL and the Southwest Research Institute.

Reference: S. Marchi et al. “The missing large impact craters on Ceres.” Nature Communications. July 26, 2016.

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Categories: Astronomy Headlines

No Dark Matter from LUX Experiment

Tue, 07/26/2016 - 11:16

An underground detector reports zero detections of weakly interacting massive particles (WIMPs), the top candidate for mysterious dark matter.

Davis Cavern

The Davis cavern, deep within what used to be the Homestake Mine, before the placement of the LUX experiment.
LUX / Sanford Underground Research Facility

Founded in 1876, the town of Lead in South Dakota hummed along as a mining community for more than a century. Homestake Mine employed thousands in the largest, deepest, and most productive gold mine in the Western Hemisphere.

Now scientists are using it to mine for gold of a darker kind.

More than a mile underground, where miners once accessed precious ore, sits a 3-foot-tall, dodecagonal cylinder of liquid xenon. The 122 photomultiplier tubes at the container’s top and bottom await the glitter of light that would signal an elusive dark matter shooting through the cylinder and interacting with one of the xenon atoms. But after more than a year of data collecting, the Large Underground Xenon (LUX) experiment announced last week at the Identification of Dark Matter 2016 conference that they’re still coming up empty-handed.

A Physicist’s Gold Mine

Weakly interacting massive particles (WIMPs) are the top candidates for dark matter, the invisible stuff that makes up about 84% of the universe’s matter. By definition, dark matter doesn’t interact with light, nor does it interact via the strong force that holds nuclei together. And while we know it interacts with gravity, that interaction leaves only indirect evidence of its existence, such as its effect on galaxy rotation.

Bottom view of LUX

This bottom view shows the photomultiplier tube holders in the LUX experiment. Find more images on LUX's Flickr account.
LUX / Sanford Underground Research Facility

But WIMP theory says dark matter particles should also interact via the weak force, a fundamental force that governs nature on a subatomic level — including the fusion within the Sun. So a WIMP particle should very rarely smash into a heavy nucleus, generating a flash of light. The chance for a direct hit is very, very low, but 350 kilograms (770 pounds) of liquid xenon in the LUX experiment should have good odds.

After just three months of operation, in 2013 the LUX experiment had already reported a null result. At the time, the experiment had probed with a sensitivity 20 times that of previous experiments (check out the graph here to see how three months of LUX ruled out numerous WIMP scenarios).

A new 332-day run began in September 2014, and the preliminary analysis announced last week probes four times deeper than the results before. Yet despite a longer run time, increased sensitivity, and better statistical analysis, the LUX team still hasn’t found any WIMPs.

Simply put: either WIMPs don’t exist at all, or the WIMPs that do exist really, really don’t like interacting with normal matter.

It’s also worth noting that LUX isn’t just looking for WIMPs. The WIMP scenario is the primary one it’s testing, and the one that last week’s announcement focused on. But more results are forthcoming about LUX results on dark matter alternatives, such as axions and axion-like particles.

Not All That’s Gold Glitters

The non-finding may not win any Nobel Prizes, but in a way it’s great news for physicists. Numerous experiments (such as CDMS II, CoGeNT, and CRESST) had found glimmers of WIMP detections, but none had found results statistically significant enough to be claimed as a real detection. The LUX results have been helpful in ruling out those hints of low-mass WIMPs.

 cross-section vs. mass plot

For the technically minded, this is the result that was presented at the Identification of Dark Matter conference in Sheffield, UK. The plot shows the possibilities for dark matter in terms of its cross-section — the bigger the value, the more easily it interacts with normal matter — and its mass. (The mass is given in gigaelectron volts per speed of light squared, which translates to teeny tiny units of 1.9 x 10-27 kg.) LUX's most recent results rule out any dark matter particles with mass and cross-section that place them above the solid black line. The upshot is that LUX, the most sensitive dark matter experiment to date, is narrowing the playing field, especially for low-mass WIMP scenarios.


“It turns out there is no experiment we can think of so far that can eliminate the WIMP hypothesis entirely,” says Dan McKinsey (University of California, Berkeley). “But if we don't detect WIMPs with the experiments planned in the next 15 years or so . . . physicists will likely conclude that dark matter isn't made of WIMPs.”

That’s why — despite not finding any WIMPs this time around — the LUX team continues to work on the next-gen experiment: LUX-ZEPLIN. Its 7 tons of liquid xenon should begin awaiting flashes from dark matter interactions by 2020.

Three years of data from LUX-ZEPLIN will probe WIMP scenarios down to fundamental limits from the cosmic ray background. In other words, if LUX-ZEPLIN doesn’t detect WIMPs, they don’t exist — or they’re beyond our detection capabilities altogether.

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Categories: Astronomy Headlines

MeerKAT in South Africa Sees First Light

Mon, 07/25/2016 - 07:00

The MeerKAT radio telescope has produced its first light image — even at quarter-strength, it’s already the best of its kind in the Southern Hemisphere.

Each white dot — totaling 1,300 individual galaxies in the distant Universe — represent the intensity of radio waves recorded with 16 dishes of the MeerKAT telescope.    MeerKAT

Each white dot — totaling 1,300 individual galaxies in the distant Universe — represent the intensity of radio waves recorded with 16 dishes of the MeerKAT telescope.

South Africa’s MeerKAT radio telescope just released its first image showing more than 1,300 galaxies in the distant universe — and that’s with only a quarter of its radio dishes operational. This is an almost 20-fold increase from the 70 galaxies in this field known prior to MeerKAT. The high-resolution images also reveal nearby cosmic phenomena happening just 200 million light years away, including a massive black hole that’s launching jets of matter at close to the speed of light.

The telescope, a precursor to the Square Kilometer Array (SKA), is being commissioned in phases to allow verification of the system. This enables scientists to quickly fix any technical issues, as well as conduct some initial science exploration. The first 16 dishes of the telescope array make up Array Release 1 (AR1). The eventual 64 dishes are expected to be in place by late 2017.

Once complete, MeerKAT will encompass 190,000 square feet (17,651 square meters) of the region outside Carnarvon, a small town on the Northern Cape of South Africa. The area is sparsely populated, but close enough to Cape Town to minimize construction and maintenance costs.

“The launch of MeerKAT AR1 and its first results is a significant milestone for South Africa. Through MeerKAT, South Africa is playing a key role in the design and development of technology for the SKA.” said Rob Adam (SKA South Africa) in a press release.

Ultimately, MeerKAT will be integrated intothe Square Kilometer Array, which when complete will be the world’s largest radio telescope. The international effort will result in a telescope tens of times more sensitive and hundreds of times faster at mapping the sky than any other radio astronomy facility. Its full array of antennas will be powerful enough to detect very faint radio signals emitted by sources billions of light-years away from Earth.

This view covers about 1% of the full MeerKAT first light image and shows a massive black hole in the distant universe — the matter falling into it produces the bright dot at the center — launching jets of powerful electrons moving at close to the speed of light that emit radio waves.    MeerKAT

This view covers about 1% of the full MeerKAT first light image and shows a massive black hole in the distant universe — the matter falling into it produces the bright dot at the center — launching jets of powerful electrons moving at close to the speed of light that emit radio waves.

SKA will be built in two phases starting in 2018. The SKA Mid-Frequency Aperture Array will be located in South Africa and will include MeerKAT’s 64 dishes, as well as another 100-plus dishes that still need to be built, all observing at frequencies from 350 MHz to 14 GHz. Australia will host SKA’s Low-Frequency Aperture Array, which will consist of about 130,000 dipole antennas observing from 50 to 350 MHz.

Together, the arrays will enable astronomers to probe the radio-emitting universe in unprecedented detail. Among other things, SKA will explore the universe’s first stars and galaxies, the role of cosmic magnetic fields, and possibly even life beyond Earth.

We’ve still got some time before SKA becomes fully operational and begins to change the face of radio astronomy, but in the meantime, MeerKAT is joining the ranks of the world’s great scientific instruments.

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Categories: Astronomy Headlines

This Week’s Sky at a Glance, July 22 – 30

Fri, 07/22/2016 - 12:59
Moon and Great Square before dawn, July 23 - 25

Take a look high in the south before dawn for the waning Moon under the Great Square of Pegasus.

Friday, July 22

• Starry Scorpius is sometimes called "the Orion of Summer" for its brightness, its blue-giant stars, and its 1st-magnitude red supergiant (Antares). But Scorpius shines a lot lower in the south (for those of us at mid-northern latitudes). That means it has only one really good evening month: July. Catch Scorpius in the south just after dark now, before it starts to tilt lower toward the southwest. It's full of deep-sky objects for binoculars and telescopes. Not to mention Mars and Saturn close by!

Saturday, July 23

• After nightfall, Altair shines in the east-southeast. Above it by a finger-width at arm's length is its eternal sidekick, little orange Tarazed. Left of Altair by a bit more than a fist-width is little Delphinus, the Dolphin, leaping leftward away from it.

Sunday, July 24

• The tail of Scorpius lies low due south right after dark. Look for the two stars especially close together in the tail. These are Lambda and fainter Upsilon Scorpii, known as the Cat's Eyes. They're canted at an angle; the cat is tilting his head and winking.

The Cat's Eyes point west (right) by nearly a fist-width toward Mu Scorpii, a much tighter pair known as the Little Cat's Eyes. It takes very sharp vision to resolve Mu without binoculars!

Monday, July 25

• The Delta Aquariid meteor shower, modest but very long-lasting, should most active for the next week or so. Under a very dark sky, you might see a dozen Delta Aquariids per hour between midnight and the first light of dawn. Each morning the light of the waning Moon will present less interference.

Tuesday, July 26

• Last-quarter Moon (exact at 7:00 p.m. EDT). The Moon rises around midnight or 1 a.m. daylight-saving time tonight, positioned near the Knot of Pisces. By early dawn Wednesday morning it stands high in the southeast.

• Are you checking the location of Nova Ophiuchi 1998, as described on page 51 of the July Sky & Telescope? It may re-explode to 10th magnitude any year now, and someone will be the first to discover this....

The consolation prize on any night are the five globular clusters in its immediate vicinity, as charted on that page.

Moon and Aldebaran at dawn, July 28 - 30, 2016

Now a waning crescent, the Moon crosses Taurus from the morning of the 28th to 30th. On the 29th it occults Aldebaran for some areas. (In these diagrams, the Moon is always drawn three times its actual apparent size for clarity.)

Wednesday, July 27

• We're not yet halfway through summer, but already W-shaped Cassiopeia, a constellation of fall and winter evenings, is climbing up in the north-northeast as evening grows late. And the Great Square of Pegasus, emblem of fall, comes up to balance on one corner just over the eastern horizon.

By the first light of dawn the Great Square stands very high in the south, almost overhead, as shown above.

Thursday, July 28

• The waning crescent Moon occults Aldebaran for observers in much of eastern North America early Friday morning. It will also occult the fainter, nearby star-pair Theta1 and Theta2 Tauri for some of the region. See your August Sky & Telescope, page 50, or the maps and timetables online for all three occultations.

Nearly a month later, on August 25th, the Moon will occult Aldebaran in daylight, as also briefly described in the August Sky & Telescope article.

Friday, July 29

• Bright Vega now passes almost straight overhead around 11 p.m. daylight-saving time, depending on your location. As with all star configurations, you'll see it happening two hours earlier every month.

Saturday, July 30

• As summer proceeds, Scorpius shifts westward from its highest stance in the south just after dark, and Sagittarius moves in from the east to take its place. So we're entering prime time for the profusion of Messier objects in and above Sagittarius. How many can you locate with binoculars?

Start with M8, the big Lagoon Nebula. It's 6° above the spout-tip of the Sagittarius Teapot.


Want to become a better astronomer? Learn your way around the constellations! They're the key to locating everything fainter and deeper to hunt with binoculars or a telescope.

This is an outdoor nature hobby. For an easy-to-use constellation guide covering the whole evening sky, use the big monthly map in the center of each issue of Sky & Telescope, the essential guide to astronomy.

Pocket Sky Atlas, jumbo edition

The Pocket Sky Atlas plots 30,796 stars to magnitude 7.6 — which may sound like a lot, but it's less than one per square degree on the sky. Also plotted are many hundreds of telescopic galaxies, star clusters, and nebulae. Shown above is the new Jumbo Edition for easier reading in the night. Click image for larger view.

Once you get a telescope, to put it to good use you'll need a detailed, large-scale sky atlas (set of charts). The basic standard is the Pocket Sky Atlas (in either the original or new Jumbo Edition), which shows stars to magnitude 7.6.

Next up is the larger and deeper Sky Atlas 2000.0, plotting stars to magnitude 8.5, nearly three times as many. The next up, once you know your way around, is the even larger Uranometria 2000.0 (stars to magnitude 9.75). And read how to use sky charts with a telescope.

You'll also want a good deep-sky guidebook, such as Sue French's Deep-Sky Wonders collection (which includes its own charts), Sky Atlas 2000.0 Companion by Strong and Sinnott, or the bigger Night Sky Observer's Guide by Kepple and Sanner.

Can a computerized telescope replace charts? Not for beginners, I don't think, and not on mounts and tripods that are less than top-quality mechanically (meaning heavy and expensive). And as Terence Dickinson and Alan Dyer say in their Backyard Astronomer's Guide, "A full appreciation of the universe cannot come without developing the skills to find things in the sky and understanding how the sky works. This knowledge comes only by spending time under the stars with star maps in hand."

This Week's Planet Roundup Saturn at opposition showing the Seeliger effect, June 5, 2016

Two days after Saturn's June 3rd opposition, Damian Peach took this image showing the Seeliger effect: the brightening of the rings with respect to the globe when the sunlight illuminating Saturn comes from almost exactly behind us. This extremely sharp image unambiguously shows the Encke Gap just inside the edge of the outer A ring, and the dusky C ring both against the globe and against the dark-sky background. The rings, practically at their widest open, extend above and below Saturn's south and north poles this season. South is up. The North Polar Hexagon's shape is clearly evident.

Mercury and Venus are very low in bright twilight. About 15 minutes after sunset, use binoculars or a wide-field telescope to start scanning for Venus just above the west-northwest horizon. Venus is magnitude –3.9; Mercury is about magnitude –0.5 (1/25 as bright), and it's fading. Look for it to Venus's upper left; they're 4° apart on July 22 and 7° by July 29.

On the 29th Mercury is about 1° to the right of Regulus, even fainter at magnitude +1.4. Good luck.

Mars (magnitude –0.9, in Libra to the right of upper Scorpius) is still bright, though fading. It's the yellow-orange light in the south-southwest at dusk, and lower in the southwest later in the evening. In a telescope, Mars is still about 13.5 arcseconds in diameter and very plainly gibbous.

Jupiter (magnitude –1.8, between Leo and Virgo) is low due west in twilight. It sets around twilight's end.

Saturn (magnitude +0.2, in southern Ophiuchus) shines in the south 6° above fainter Antares at dusk, and about 13° upper left of brighter Mars. Near the middle of the Mars-Saturn-Antares triangle is the strange variable Delta Scorpii (Dschubba), the middle star of the nearly vertical row marking the Scorpion's head.

See our telescopic guide to Saturn in the June Sky & Telescope, page 48.

Uranus (magnitude 5.8, in Pisces) and Neptune (magnitude 7.8, in Aquarius) are very high in the southeast to south before the first light of dawn. Background and finder charts.


All descriptions that relate to your horizon — including the words up, down, right, and left — are written for the world's mid-northern latitudes. Descriptions that also depend on longitude (mainly Moon positions) are for North America.

Eastern Daylight Time (EDT) is Universal Time (UT, UTC, or GMT) minus 4 hours.


“This adventure is made possible by generations of searchers strictly adhering to a simple set of rules. Test ideas by experiments and observations. Build on those ideas that pass the test. Reject the ones that fail. Follow the evidence wherever it leads, and question everything. Accept these terms, and the cosmos is yours.”

— Neil deGrasse Tyson

The post This Week’s Sky at a Glance, July 22 – 30 appeared first on Sky & Telescope.

Categories: Astronomy Headlines

Dark Streaks on Mars Revisited

Fri, 07/22/2016 - 11:03

New research on seasonal streaks in Martian canyons provides evidence against underground pools of water.

The white arrows point out the seasonal dark streaks, called recurring slope lineae (RSL), on the surface of Mars. The Valles Marineris region has the densest population of streaks on the Red Planet. NASA / JPL-Caltech / University of Arizona

The white arrows point out the seasonal dark streaks, called recurring slope lineae (RSL), on the surface of Mars. The Valles Marineris region has the densest population of streaks on the Red Planet.
NASA / JPL-Caltech / University of Arizona

Since 2011, astronomers have seen dark streaks appear and fade on the surface of Mars. These dark streaks, called recurring slope lineae (RSL), show up on the planet’s steep slopes during the warmer months and fade during the colder months. This happens year after year.

Planetary scientists suspected brines were somehow involved (pure liquid water can’t survive on Mars’s surface). But no one really knew until last September, when Lujendra Ojha (Georgia Institute of Technology) and others confirmed that these warm-season features contain water-soaked salts.

Now, Matthew Chojnacki (University of Arizona) and other members of Ojha’s team have taken the next step in understanding these mysterious flows. They investigated thousands of streaks in 41 sites of the Valles Marineris region, the largest canyon system in the solar system. There the team found that pretty much all of the walls of the canyon system, including the sides of isolated peaks, had RSLs. “As far as we can tell, this is the densest population of them on the planet,” says Chojnacki in a press release.

If Ojha’s paper is saying, ‘blame salty water for RSL’, Chojnacki’s paper is saying, ‘Guys, they’re everywhere and not quite what we expected.’ Their work gave proof that underground pools of water weren’t responsible for RSL. Instead, it’s more likely that the water is coming from the atmosphere.

RSL and Liquid Water

Since their discovery, RSL have been a popular topic in planetary exploration and the strongest evidence of liquid water on Mars. One hypothesis for RSL formation that had people excited is that they form when underground bodies of salty water leak onto the surface. “[This] is exciting because those aquifers could be habitable environments for some very, very salt-hardy microbes,” says planetary scientist Briony Horgan (Purdue University), who wasn’t involved with the study.

Water could also become an important resource for humans living on the Red Planet. If RSL really are indicators of water, then it means humans may have access to water at least around the Valles Marineris region. This area stretches over 4,000 km (2,500 mi) across Mars, mostly east-west and just below the equator.

But the team found streaks on canyon ridges and even isolated peaks. “It's really hard to imagine how an aquifer could be sustained near the tops of isolated mountains, so this observation casts some doubt on that theory,” says Horgan.

RSL and the Martian Atmosphere

One alternative is that the salts on the Martian surface are pulling water from the atmosphere. This process is called deliquescence. Scientists have suggested it before to explain signs of water action on the Red Planet.

If the Martian atmosphere is a possible source of water, then there’s a slight issue with the math. Chojanacki’s team estimates that about 10 to 40 Olympic-sized swimming pools (30,000 to 100,000 cubic meters) of water are required to make the streaks. Based on orbiter estimates, there’s enough water vapor floating above Valles Marinies for that to happen, but researchers can’t think of an efficient way for the surface to extract that much water from the atmosphere.

On the other hand, if this amount of water is coming from the atmosphere, then maybe we’ve underestimated how much is there. “This could mean that there are places on Mars that are more humid than we realized, and that just maybe there's enough water in the atmosphere to serve as a resource for future human exploration,” says Horgan.

Chojnacki’s study was published in the July 7 issue of Journal of Geophysical Research: Planets.

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Categories: Astronomy Headlines

Inside the September 2016 Issue

Fri, 07/22/2016 - 06:45

SKY1609Weak Lensing, Big Data, and Beautiful Planets

Google "gravitational lensing" and you'll uncover a trove of magnificently distorted galaxies, their images twisted under the spell of gravity. But it's the far tinier warping of galaxy images in weak gravitational lensing that motivates our cover story by S&T Contributing Editor Govert Schilling. Tried-and-true techniques are being applied to a bevy of large surveys with the promise of breakthroughs on dark matter and dark energy. Large surveys like these are also the source of a gathering storm for the astronomical community — Big Data — an issue Editor in Chief Peter Tyson faces in his feature. Big data isn't just for the pros — record video of the Sun, Moon, or planets for sharp images, and an amateur could collect more than 100 gigabytes of data in a single night. Learn how to stack the best frames of your video with only a few clicks. And as always, in this issue you'll find guides to the sky whether your instrument of choice is a 10-inch reflector, a pair of binos, or just your eyes.

Feature Articles Galaxy cluster Abell 1689

Astronomers use weak gravitational lensing to map the distribution of dark matter (purple overlay) in galaxy clusters such as Abell 1689.

Astronomy & Big, Big Data
How will astronomers cope with the tsunamis of raw data soon to pour in from wide-field surveys?
By Peter Tyson

Observing Through a Truly Large Telescope
The author and friends enjoyed a memorable night of observing through what was once the world's largest telescope.
By Robert Naeye

Find Your Dawes Limit
The famous resolving-power rule for telescopes may not apply to you. Try these close double stars to find out.
By Phillip Kane

Strong Prospects for Weak Lensing
Astronomers are mapping tiny distortions in teh images of distant galaxies to study the invisible — dark matter and dark energy.
By Govert Schilling

Planetary Processing with Autostakkert! 2
This freeware takes the drudgery out of stacking planetary videos.
By Emil Kraaikamp

Beyond the Printed Page Juno at Jupiter

NASA / JPL-Caltech

Shoot Time-Lapse Movies (VIDEO)
Learn time-lapse astrophotography using the iPano mount from iOptron.

Aid Juno at Jupiter
Amateur astro-imagers can help planetary scientists enhance Juno's data.

Watch Kuiper Belt Object OR10 (VIDEO)
See Kepler's observations of this icy rock tumbling in the farthest reaches of the solar system.

Lunar Librations
Librations and other lunar data for September 2016.

ALSO IN THIS ISSUE Profile of asteroid 8 Flora

Observers of asteroid occultations can combine their data to map the shape of these space rocks, as was done during the occultation of a 9th-magnitude star by the asteroid 8 Flora on October 29, 2004.

Parting Ways
Mercury & Jupiter exit, but Venus, Mars, and Saturn still grace the nightfall.
By Fred Schaaf

Map Asteroid Shapes by Video
Join the worldwide project to time asteroid occultations precisely — it's cheaper and easier than ever.
By Alan MacRobert

Uranus Ascending
Careful observing reveals this distant planet as more than a simple disk.
By Kevin Bailey

Lonely Hearts of Summer
Visit some of these less-frequented destinations this season.
By Sue French

Table of Contents
See what else September's issue has to offer.

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Categories: Astronomy Headlines

Mars 2020 Rover Construction Moves Ahead

Thu, 07/21/2016 - 08:15

The Mars 2020 rover reaches a third milestone on the path to the launch pad.

Mars 2020 rover

An artist's concept of the Mars 2020 rover in action.

Things are getting real now. Last week, NASA announced that it will proceed with the final design and construction of the Mars 2020 rover. The announcement comes after intensive engineering and design studies that evaluated proposals for instrument packages.

Set to launch in the summer of 2020, the as-yet unnamed Mars 2020 rover will arrive at the Red Planet for its very own "seven minutes of terror" by February 2021. And it has now reached the third of four Key Decision Points on the long road to the launch pad. Phase A was the concept and requirements definition and Phase B was preliminary design and technology development. Now NASA has approved its entry to Phase C, the final design and fabrication of the actual rover. (The final Phase D will include assembly, integration, and testing leading up to launch.)

“The Mars 2020 rover is the first step in a potential multi-mission campaign to return carefully selected and sealed samples of Martian rocks and soil to Earth,” says Geoffrey Yoder (NASA Science Mission Directorate) in a recent press release.

Mars 2020 Instruments

We're also now getting a good look at just what instrument packages will make the cut.

Unlike Curiosity, Mars 2020 will explicitly look for signs of life, past and present. The primary goal of the mission is motivated by exploring regions where life could have existed. To this end, the Mars 2020 rover will carry a suite of instruments from institutions in the U.S., France, Spain, and Norway. This vehicle weighs in at about 1,050 kilograms, the heaviest payload fielded on any planetary surface yet. (It beats Curiosity by 150 kg).

Like Curiosity, the Mars 2020 rover is equipped with a powerful laser and drill, complete with replacement bits. This isn't your parent's Mars rover, however.

Mars 2020 rover

A look at the new design for the Mars 2020 rover.
NASA / JPL-Caltech

Here's a rundown of what's onboard Mars 2020:

PIXL: The Planetary Instrument for X-ray Lithochemistry: This X-ray fluorescence spectrometer will enable high resolution analysis of soil samples. The Mars 2020 mission will also package and cache the soil samples it collects for a later potential sample return mission.

RIMFAX: The Radar Imager for Mars' subsurFAce eXperiment generates powerful ground-penetrating radar that will probe below the rover to a depth of several dozen meters.

MEDA: The Mars Environmental Dynamic Analyzer, this instrument package will provide extensive meteorological measurements, including wind direction, speed, temperature, pressure, humidity, and dust particle shape and size during dust storms.

MOXIE: The Mars Oxygen ISRU Experiment (yes, an acronym containing acronyms!) will test the ability for future astronauts to "live off the land," producing oxygen from carbon dioxide drawn from the tenuous Martian atmosphere.

SHERLOC: The Scanning for Habitable Environments with Raman and Luminescence for Organics and Chemicals. This is the potential "life-finder," which will utilize fine scale UV-imaging in the search for organic compounds.

SuperCam: This instrument will image and analyze the chemical composition of the surrounding terrain, as well as detect the presence of organic compounds in rocks and regolith from a distance.

A new and improved stereoscopic imaging system known as Mastcam-Z will also scan the terrain around the rover in high-definition detail. Though previous rovers weren't meant to scan the skies, they've proven to be serendipitous Martian astronomers as well, nabbing images of the fleeting Martian moons.

phobos transit

Phobos transits the Sun as seen by Curiosity.
NASA / JPL-Caltech / Malin Space Science Systems / Texas A&M Univ.


The sky crane Entry Descent and Landing (EDL) phase for Mars 2020 also borrows from Curiosity's historic landing procedure. An onboard range trigger will allow for a parachute from the rover to open on command after terrain analysis. Curiosity opened its chute only when it hit a certain descent speed. Mars 2020 will do the same, but it will have an estimated 50% smaller landing ellipse. It'll also have the option of diverting its landing site if it spots hazards. We should see some amazing video shot not only from the sky crane as the rover descends, but from the rover looking back up at the chutes as they deploy.

Mars 2020 will, like Curiosity, sport a plutonium-238 powered Multi-Mission Radioisotope Thermoelectric Generator. This will give it an estimated 10-year operational life span (Pu-238 has a 87.7 year half-life). NASA is experiencing a plutonium shortfall, and the Department of Energy only in 2013 announced that it would restart the plutonium production pipeline for U.S. space exploration. Curiosity actually used plutonium purchased and re-purposed from the Russians. (Note: the Pu-239 isotope is the fissile weaponized version and, unfortunately, can't be reused in RTGs).

NASA has yet to announce a formal name for the Mars 2020 rover, but a naming campaign similar to the one that christened Curiosity will get underway later this year. Landing site selection is also currently in progress, with sites narrowed down to eight regions. A final decision should be announced in July 2019. There's always a bit of tension in this process, as engineers prefer to land in safe areas, while scientists would love to go explore interesting (and more rugged) terrain.

Mars Microphones & Helicopter Drones

A set of microphones will also fly to Mars in 2020. What does a Martian dust storm sound like? What noises does a rover make, as it creaks along? The Mars 2020 mission will let us hear for the very first time the sounds that accompany the sights from the surface of a brave new alien planet.

The road to put a microphone on another world has been a long one. The Mars Polar Lander featured a microphone, but the rover crashed on descent on December 3, 1999. Its predecessor, the Mars Phoenix Lander, delivered a microphone intact to the Martian surface, installed on the MARDI descent imager package, but engineers switched it off due to concerns that MARDI would interfere with other crucial electrical systems. The acoustic sensor aboard ESA's Cassini-Huygens mission did return some very brief audio during its descent through the atmosphere of Saturn's large moon, Titan. The addition of microphones to Mars 2020 rover gives us a new chance at hearing an alien world.

Meanwhile, though NASA has been funding the development of helicopter drones, there's no official word yet if one would head to Mars in 2020. Such a drone would make short scouting flights, using the 2020 rover as a base for operations.

The Next Mars Orbiter

Another key announcement came out this week, as NASA selected five U.S. aerospace companies to compete in a four-month concept study to develop the next-gen Mars orbiter.

“We're excited to continue planning for the next decade of Mars exploration,” said Yoder in a press release.

NASA has a fleet of aging orbiters circling the Red Planet, including MAVEN, the Mars Reconnaissance Orbiter, and Mars Odyssey, which has been orbiting Mars for an amazing 14 plus years. Newer missions include the European Space Agency's ExoMars Trace Gas Orbiter, due to arrive in September, and India's Mars Orbiter Mission. In addition to research, a future NASA orbiter would provide essential communications relays with the surface.

Get ready to invade Mars!

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Categories: Astronomy Headlines

Antonín Rükl, 1932–2016

Wed, 07/20/2016 - 09:05

A world-renowned lunar cartographer, whose beautiful atlases have become prized possessions, has died at age 83.

Known worldwide for his lunar cartography, in 2012 Antonín Rükl was given Cena Františka Nušla — teh Czech Republic's highest award for astronomical achievement.Vladimír Libý / Prague Planetarium

Known worldwide for his lunar cartography, Antonín Rükl received Cena Františka Nušla in 2012 — the Czech Republic's highest award for astronomical achievement.
Vladimír Libý / Prague Planetarium

Antonín Rükl, noted lunar cartographer, selenographer, prolific author, and retired director of the Prague Planetarium, passed away on July 12th at his home in Prague, Czech Republic.

Rükl's loss is being deeply felt by anyone who loves looking at the Moon. Among the books he authored, his legendary Atlas of the Moon, originally published in 1991 and most recently revised in 2007, remains one of the most sought-after books of its kind.

His astronomical maps, atlases and picture publications were published not only in the Czech Republic but were also translated into many languages and published abroad.

<i>Atlas of the Moon</i> by Antonín Rükl

The 2007 edition of Antonín Rükl's Atlas of the Moon is highly prized by lunar observers.
Sky & Telescope

Besides his much-admired lunar atlas, an incomplete list of Rükl's other books includes Skeleton Map of the Moon, 1:6000000 (1965), Maps of Lunar Hemispheres, 1:10000000 (1972), Moon, Mars and Venus (1976), The Amateur Astronomer (1985), Hamlyn Encyclopedia of Stars and Planets (1988), Hamlyn Atlas of the Moon (1991), The Constellation Guide Book (1996), and A Guide to the Stars, Constellations and Planets (English edition, 1998),.

Rükl was born in Čáslav, Czechoslovakia, on September 22, 1932. His keen interest in astronomy began as a student hobby when he was 17 years old. He graduated from Czech Technical University in Prague in 1956, after which he joined the Czech Technical University as a staff member, working at the Prague Planetarium in February 1960. Rükl became head of the planetarium shortly after its establishment, holding that position until late 1999 when he "semi-retired." Even then, according to a statement released after his death, Rükl continued to work on planetarium programs until his last days.

Rukl with Ken Poshedly and Walter Haas

During a visit to U.S. in 2000, Antonín Rükl (center) and the late Walter Haas (right) visited author Ken Poshedly and his 20-inch reflector.
Ken Poshedly

Besides a planetarium directors' conference in 1999 in Florida, Rükl's only other visit to the U.S. was as the keynote speaker at the Atlanta Astronomy Club's Peach State Star Gaze in April 2000. At that event, more than 200 attendees gathered to attend his two presentations on how he researched and prepared the scrupulously detailed maps for his lunar atlas. In addition to his knowledge and professionalism, what impressed everyone was his humble and unpretentious demeanor. For example, after the daytime talks, he walked the observing field each night on his own, chatting with attendees, autographing their copies of his lunar atlas, and even peering through their scopes at the evening's young Moon.

Prior to the PSSG event, Rükl had privately communicated to the event organizers that he himself had no telescope of his own and asked for advice on what he might consider purchasing. Instead, a group of AAC members pitched in to surprise Rükl with his own Meade ETX scope at the event. It was also there Rükl received a lifetime membership in the Association of Lunar & Planetary Observers (ALPO). Also in 2000, minor planet 15395 was named for this beloved lunar specialist.

Afterward, he said that felt more honored here in the U.S. than he was back home. However, in 2012 he was given Cena Františka Nušla — the Czech Republic's highest award for astronomical achievement.

Rükl's wife, Sonja, passed away several years ago. They are survived by a daughter (Jana), a son (Michal), and four grandchildren.

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Categories: Astronomy Headlines

IC 5146 Cocoon Nébula

Wed, 07/20/2016 - 07:34

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Categories: Astronomy Headlines

See Two Tricky Occultations — Neptune and Lambda (λ) Aqr

Wed, 07/20/2016 - 07:15

Now you see 'em, now you don't. Watch the Moon occult Neptune and nearby Lambda Aquarii on the same night.

Moon Magic

On July 22-23, the waning gibbous moon occults Neptune, here shown during its simulated reappearance. The planet's tiny 2.3″ aqua disk is dwarfed by the Moon.

I love magic. It always makes me feel so dumb. That's probably because I'm terrible at figuring out magic tricks. Levitating tables? Death saw? Keep 'em coming! A favorite trick is to make a quarter disappear and then pull it out of someone's ear, a ruse that finds its counterpart in the night sky.

On Friday night–Saturday morning July 22-23, the magician Moon performs a classic magic act when it will make both Neptune and Lambda (λ) Aquarii disappear for about an hour (or less depending on your location) and then return them to view no harm done. Because the Moon will be 88% illuminated at the time, seeing the bright side disappearance will be relatively easy for the star, which shines at magnitude +3.7, but all but impossible for Neptune at +7.8.

Quick Look Map

This color-coded map shows where the Neptune occultation will be visible. Cyan = occultation at moonrise/moonset; red dotted = daytime occultation; blue = twilight occultation; and white = nighttime occultation. Click the image for a list of cities and times of the planet's reappearance at the Moon's dark limb.
Occult 4.1

Fortunately, both will be visible during their reappearance at the moon's dark limb. A small scope will show the star, but you'll need an 8-inch or larger telescope with clean optics (to minimize scattered light) to nab the planet. Even then it will be a challenge. Both occultations occur within about a half hour of each other with Neptune going first. Interestingly, since both objects are just 30′ apart on that night, the Moon almost glides right between them. But not quite. Because the Moon is near perigee with a diameter of 32′  that evening, it either occults one and narrowly misses the other, or occults both!

Tale of Three Cities

Here's the view from three different cities: Quebec, Chicago, and Jackson, Mississippi. Times noted are when Neptune reappears at the Moon's dark limb at lower right. Jackson is far enough south that the Moon also occults Lambda Aqr (hidden).
Maps: Bob King; Source: Stellarium

What you'll see depends on your location, which causes the Moon's apparent position to shift this way or that against the more distant background stars, a phenomenon called parallax. Since we're mostly interested in the reappearances of the star and planet, we'll focus on that aspect of the occultation. Neptune returns to view along the Moon's southeastern limb (southwest side in "Earth" directions) around 5:35 UT or 12:35 a.m. EDT July 23rd from many locations across the eastern two-thirds of North America (except Florida).

Double Dissappearance and Reappearance

From Atlanta, both Neptune and Lambda Aqr will reappear at 12:24 a.m. and 12:38 a.m. EDT, respectively, after being occulted by the Moon.
Map: Bob King; Source: Stellarium

Observers on a line from central Texas through central Louisiana and across southern Mississippi, Alabama, and Georgia will witness a grazing occultation, with Neptune scraping along the moon's southern limb.

Not long after the Moon covers Neptune, it will also occult Lambda Aqr for observers in the southern states, Central America, and northern South America. Disappearance will take place around 4:30 UT (11:30 EDT) and reappearance about 5:45 UT (12:45 EDT).

The northern graze line cuts across northern New Mexico and continues through central Oklahoma, Arkansas, Tennessee, and North Carolina. Anywhere north of this line, the Moon misses Lambda, passing just below the star. Skywatchers living south of the Lambda's graze line and north of Neptune's get to see both reappearances!

Visibility zones for Two Occultations

This map shows the visibility limits for the reappearances of Neptune and Lambda Aqr at the Moon's dark limb after occultation. South of the Neptune limit, the planet won't be occulted; north of the Lambda limit, the star won't be occulted.  Both will be occulted and reappear at the Moon's dark limb for observers living between the two limits.
Bottom curve and map: David Dunham, David Herald, Occult software; top curve adapted from the Curt Renz map

What to do if you live in the western U.S. and Canada where the Moon doesn't rise until well after Neptune's reappearance? Use the opportunity to make easy work of finding Neptune. You'll spot it just ½° to  ¾° due west of the Moon. For that matter, observers in the far southern U.S., where no occultation will occur, can still use the Moon to find the planet, located a few arcminutes south-southwest of the lunar limb. Neptune displays a pale blue disk through a 4-inch and larger telescopes when viewed at 100x or higher.

Stay on Neptune's Track

Use this map to keep track of Neptune's whereabouts through mid-October as it ambles southeastward from Lambda Aqr. Positions are shown for 11 p.m. CDT every 10 days. Stars shown to magnitude +9.5. North is up.
Chris Marriott's SkyMap software

Once the Moon departs the area two nights later, Neptune remains within about ½° of Lambda through month's end, making it an easy catch in telescopes and binoculars any clear night. Center Lambda in your low power telescopic field of view and the pale blue planet will appear a short distance to the SSW. With a 10-inch or larger telescope and magnification of around 200x, try digging out Neptune's brightest moon Triton at magnitude +14. It's not as hard you might think! To help pinpoint its location and confirm your observation check out Sky &Telescope's Triton Tracker. You can also download S&T's Neptune finder chart to track the ice giant into the fall and winter.

Even though the solar system's most remote planet comes to opposition on September 2nd, let yourself get swept up in some Neptunian magic early. The occultation also serves as a preview for a striking dawn conjunction and occultation of Aldebaran by the crescent Moon on July 29th.  Clear skies!

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Categories: Astronomy Headlines

Heart of Cygnus

Tue, 07/19/2016 - 14:19

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Seeing a Black Hole’s Gravitational Vortex

Tue, 07/19/2016 - 07:59

New observations solve a 30-year-old puzzle of mysterious signals from around black holes.

An artist's conception of a supermassive black hole. NASA/JPL-Caltech

An artist's conception of a supermassive black hole.

Strange things happen around black holes, especially spinning ones. Their strong gravitational pull means they don’t just pull in gas to munch on — they drag the very fabric of spacetime around them as they spin.

Every rotating massive body does this — even puny Earth, as measured by the Gravity Probe B. But around black holes the so-called frame-dragging effect (also known as the Lense-Thirring effect) is particularly strong. Like flies stuck in honey, anything embedded in that spacetime will get dragged along, too. And now, with new observations from the XMM-Newton and NuSTAR space telescopes, astronomers have connected the effect to long-mysterious signals seen around stellar-mass black holes.

Black Hole Beats Quasi-Periodic Oscillation

This artist's impression depicts an accretion disk surrounding a black hole. The black hole drags spacetime with it as it spins. So X-ray-emitting plasma near the black hole, stuck in spacetime like a fly stuck in honey, precesses. The X-rays strike matter in the surrounding disk, making it to glow like a fluorescent bulb. The glow appears to rotate around the accretion disc to the right (top), to the front (middle), and to the left (bottom).
ESA / ATG medialab

While we can’t see black holes directly, we can see those that are guzzling gas. Such meals are easy to come by for black holes in binary systems, as they pull mass from their unlucky companion stars. As the gas spirals inward, it heats up: the closer it comes to the black hole, the hotter the gas will be, and the higher the frequency of the photons it radiates. Very near the black hole, the plasma reaches a fevered pitch, puffing up and emitting energetic X-rays.

Back in the 1980s, astronomers started seeing signals amidst these flickering X-rays that looked suspiciously regular. Dubbed quasi-periodic oscillations, these QPOs seemed to come from something whizzing intriguingly close-in around the black hole. More than a decade later, an idea emerged: astronomers could be witnessing the frame dragging effect in action.

Here’s the general picture: hot puffed-up plasma very near the black hole radiates X-rays. Some of these X-rays hit the surrounding gas disk, knocking electrons off of iron atoms in the swirling gas. As those iron atoms snatch back their electrons, they fluoresce, emitting X-rays at a specific energy.

The whole system — the black hole, the hot inner plasma, and the surrounding disk — is spinning like a top. And if the disk is tilted relative to the black hole, then the top will wobble, or precess. We’ll see the hot plasma fluoresce off of part of the outer disk, and that fluorescence will appear to rotate around the black hole. When we’re seeing a part of the disk spinning around toward Earth, we’ll see its iron emission blueshifted; emission from a part of the disk spinning away again will shift redward.

Adam Ingram (University of Amsterdam, The Netherlands) and colleagues set out to observe this effect directly. They pointed the XMM-Newton and NuSTAR space telescopes at the system known as H1743-322, where a black hole with a mass of about 10 Suns is drawing in gas from its companion star. Four of the five observations clearly show the iron line shifting back and forth in the spectrum over the course of 4 to 5 seconds, exactly in the way that the frame-dragging effect predicts.

“This is a very intriguing result,” says Laura Brenneman (Harvard-Smithsonian Center for Astrophysics), who was not involved with the study. “Certain types of QPOs in X-ray[-emitting black hole] binaries have long been suspected to arise from some form of precession, but this result is the closest thing I've seen to hard evidence for that.”

This result turns stellar-mass black holes into a proving ground for new physics. “If you can get to the bottom of the astrophysics, then you can really test general relativity,” Ingram said in NASA’s press release, welcome news to physicists who are searching for a deeper theory of gravity.

One of These Is Not Like the Others

Over 3 days’ worth of exposure, XMM-Newton collected five sets of data. While four of these matched beautifully, one, known as orbit 1b, didn’t conform at all to expectations. It could simply be that some gas obstructed the astronomers’ view, or it could be that the observation is telling astronomers something more fundamental.

“I am curious as to what is going on in XMM-Newton’s orbit 1b that is so anomalous compared to the others,” Brenneman adds, “but I don't think it diminishes the result at all, just adds an extra dimension and opens up more questions.”

Another intriguing aspect of QPOs is that they’ve (almost) never been seen in the supermassive variety of black holes. These active galactic nuclei (AGN) guzzle gas at the center of galaxies with the same setup as stellar-mass black holes: a black hole, a gas disk, and X-ray-emitting plasma. The only thing they’re missing is the binary companion star.

“There has only been one reputable claim of a QPO in an AGN back in 2008, and it hasn't been seen again since,” Brenneman says. “If there were QPOs-a-plenty in AGN, we would likely have detected them by now.” Why they aren’t there, no one knows.

With one mystery solved, it’s clear there are still more cases awaiting closure.


Adam Ingram et al. "A quasi-periodic modulation of the iron line centroid energy in the black hole binary H 1743-322", Monthly Notices of the Royal Astronomical Society, 2016 May 25.(Full text)

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Categories: Astronomy Headlines

The Town-Sized Milky Way Project

Mon, 07/18/2016 - 13:35

I turned my town into a model of the Milky Way Galaxy for my high school astronomy project.

Grace Hoaglund picked the Robbins Library in Arlington, MA as the center of her town-sized model of the Milky Way Galaxy.   Nick Greenhalgh

Grace Hoaglund picked the Robbins Library in Arlington, MA as the center of her town-sized model of the Milky Way Galaxy.
Nick Greenhalgh

If you had told me at the beginning of the year that my high school astronomy project would land me in the local paper, I wouldn’t have believed you.

This was partly because I didn’t even plan on taking astronomy. I’m a humanities kid through and through, lover of fantasy novels and other things decidedly unscientific. I planned on taking the least “mathy” class to fulfill my science requirement. But alas, there was a scheduling conflict, and so I opted for a half-year astronomy class.

Looking back, this was probably the best scheduling conflict of my life.

In a year of great courses, astronomy was one of my favorites. We explored the solar system, learned how stars live and die, and calculated the age of the universe. We speculated about exoplanets and extraterrestrial life. We got to have discussions about current events in astronomy, like when water was discovered on Mars. Sure, there was math, but it wasn’t impossible to understand.

For my final term project, I knew I wanted to do something none of my classmates had done. I ultimately decided I wanted to turn my town, Arlington, Massachusetts, into a scale model of the Milky Way Galaxy.

The Mass Ave Milky Way Project was named after a major street in our town - Massachusetts Avenue, or Mass Ave for short. The premise was relatively straightforward: if the Milky Way was the size of our town, where would various objects like star clusters and nebulae be? The idea was that as people walked and saw all the posters around town, they would learn different things in our galaxy, and gain a better understanding of the awe-inspiring scale of things in space. Everything would be unified on a website listing the location of each poster. As a bonus, if people sent in pictures of themselves at every location, I would send them a special prize.

One of Grace Hoglund's signs hangs in a restaurant in downtown Arlington, MA. The Zone of Avoidance is the area of the night sky that's obscured by the Milky Way.  Nick Greenhalgh

One of Grace Hoglund's signs hangs in a restaurant in downtown Arlington, MA. The Zone of Avoidance is the area of the night sky that's obscured by the Milky Way.
Nick Greenhalgh

I am, of course, not the first to make a model to explain the vastness of space. My local Museum of Science has a solar system model, which starts at the museum and spans most of Boston. It seems that large-scale models of the Solar System vastly outnumber those of the Milky Way. I think this is quite a shame, as Milky Way models aren’t that hard to construct.

If you want to do your own scale model of the Milky Way, all you need is a little middle-school math. I sketched the whole thing out on a map of my town. For the sake of simplicity, I decided to assume that everything was on a single plane - I love astronomy, but I’m not about to try and climb any telephone poles to demonstrate the relative thickness of the Milky Way. I picked a center point (the local library), got out a protractor, and drew a two-mile-wide circle around it. Everything after that was basic scaling: 5 inches on the map is to 2 miles in town is to 100,000 light years in space. The nearby branch library was conveniently located right where our solar system needed to be.

Filling out the galaxy then got a little complicated. I had three basic criteria for what went on the map: 1) could I explain it easily, 2) could I locate it, and 3) was there a picture. Constraints one and three meant that most of my objects were stars, star clusters, or nebulae. All of these are pretty easy to explain, and NASA has a wealth of images available. Plus, those kinds of objects are (scientifically speaking of course) really cool. Eta Carinae, for instance, is a binary star system with a luminous blue variable star, whose brightness changes over time. The red giant Betelgeuse is more than 900 times the size of our Sun. Even someone who’s never studied astronomy can look at something like that and appreciate just how amazing and alien outer space is.

Location, though, became a bit of an issue. For most objects, especially stars, it was easy to find the distance of the star from Earth. However, that doesn’t tell you much about what part of the galaxy it’s located in. I ended up approximating that based on a poster of the Milky Way by National Geographic, which featured the specific locations of various galactic features.

The hardest part for me was setting up the model. For each item on the map (I had nine) I typed up a small blurb about it and made a poster. Then, map in hand, I went around to the location of each star cluster/nebula/etc. and proceeded to essentially solicit nearby businesses. It was hard to come up with an elevator pitch; I ultimately landed somewhere between “help me introduce the masses to the wonders of our galaxy and bring them a new appreciation of the cosmos” and “help me get an A”. Explaining things could be complicated, as I learned while trying to describe the Zone of Avoidance to a harried cashier. But most places were actually really interested in the project - I guess it’s kind of cool to learn that, for instance, your bakery is right where one of the brightest stars in our sky is located. And when there wasn’t a friendly local business, I made due duct-taping a poster of the Eagle Nebula to my best friend’s tree.

Residents of Arlington, MA attempting to complete the Milky Way Galaxy Project challenge found signs in all kinds of places.  Nick Greenhalgh

Residents of Arlington, MA attempting to complete the Milky Way Galaxy Project challenge found signs in all kinds of places.
Nick Greenhalgh

Of course, I had other helpers. Instrumental to the project was my teacher, Mr. G who, among other things, helped me find relevant and easy-to-understand information, and also let me do the project in the first place (which was really quite nice of him, considering the fact that I approached him with only a weird idea and no clue how to carry it out). And then there was Nick Greenhalgh, local newspaper reporter, who asked me if he could publish an article on The Mass Ave Milky Way.

But of course!

The article was great, and even better was the fact that it alerted the wider public to the project. In the weeks after, five different people came forward to show that they had visited each site, ready to claim their prizes.

I will acknowledge that five is not a large number. Three were a couple and their infant son, one was an 8-year-old girl, and one was an 11-year-old girl who adored astronomy and was holding a stuffed Sun toy in all of her photos. If this project kept people like that interested in science and astronomy, then I think it was absolutely worth every minute I put into it.

The Mass Ave Milky Way Project is over now, since I’m moving away and then going off to college. The signs around town are gone, and website extends its thanks to all those who participated. But it continues to be one of the most enjoyable and inspiring things that I’ve done during my high school career. And the best part is, now that I know how to make a scale model of the Milky Way, I can do it again, wherever I go next.

Oh, and as for those prizes I mentioned? The ones I sent to people if they visited every poster? They were, of course, Milky Way bars.

Grace Hoglund is a recent graduate of Arlington High School who will be attending Seattle University in the fall. She currently plans to major in English, with eventual hopes of becoming a librarian.

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Categories: Astronomy Headlines

The Making of a “Frankenstein” Galaxy

Mon, 07/18/2016 - 11:38

Astronomers take a second look at UGC 1382 — previously considered a typical elliptical galaxy — and reassess everything they know about its size, age, and formation.

In optical light (left), UGC 1382 appears to be a simple elliptical galaxy. But when astronomers used ultraviolet and deep optical data (middle), spiral arms emerged. When it was combined with a view of low-density hydrogen gas (seen in green at right), scientists discovered UGC 1382 is bigger than expected.  NASA / JPL / Caltech / SDSS / NRAO / L. Hagen and M. Seibert

In optical light (left), UGC 1382 appears to be a simple elliptical galaxy. But when astronomers used ultraviolet and deep optical data (middle), spiral arms emerged. When it was combined with a view of low-density hydrogen gas (seen in green at right), scientists discovered UGC 1382 is bigger than expected.
NASA / JPL / Caltech / SDSS / NRAO / L. Hagen and M. Seibert

We all know the story: a crazy scientist named Frankenstein creates a monster by assembling different human parts. Now, astronomers have found a similar “Frankenstein” galaxy about 250 million light-years away in a quiet and unremarkable neighborhood — butthis Frankenstein is beautiful!

The monster galaxy, UGC 1382, was originally thought to be old, small, and typical of other elliptical galaxies. Several surveys done in the 2000s looked for structural features like star rings and bars but didn’t find anything other than a simple elliptical galaxy. Then Lea M. Hagen (Pennsylvania State University) noticed something interesting about UGC 1382 when her team was investigating star formation in early-type galaxies.

Using NASA’s Galaxy Evolution Explorer (GALEX), which images the universe in ultraviolet, they noticed UGC 1382 had very extended spiral arms. Further investigation using optical and infrared light observations showed it was actually ten times bigger than previously thought and, unlike most galaxies, its innermost stars are younger than the stars on the outskirts. It’s almost as if the galaxy had been built using spare parts — like Frankenstein.

"This rare 'Frankenstein' galaxy formed and is able to survive because it lies in a quiet little suburban neighborhood of the universe, where none of the hubbub of the more crowded parts can bother it," said Mark Seibert (Observatories of the Carnegie Institution for Science) in a press release. The galaxy is so delicate that even a small nudge from a neighboring galaxy would make it disintegrate.

Frankenstein’s Formation

In most galaxies, the innermost region forms first and has the oldest stars. As time goes on, newer stars form in the outer regions of the galaxy. But this wasn’t the case with UGC 1382. Instead of a crazy scientist putting pieces together, this unique galaxy may have been the result of separate entities merging together — each with its own history.

First, a group of dwarf galaxies composed mostly of gas and dark matter formed. A rotating galaxy without spiral arms, called a lenticular galaxy, came together nearby. Then, at least 3 billion years ago, the smaller galaxies fell into orbit around the lenticular, eventually becoming its spiral arms. This process would make the center of UGC 1382 younger than the spiral disk surrounding it.

But Lynn Matthews (Haystack Observatory) says one has to be cautious with this scenario. It’s difficult to find the precise age of a galaxy because stars form at different times and that process doesn’t always go smoothly. The amount of heavy elements, or metallicity, present in the galaxy can also impact the ages of the stars. “What the authors have shown so far is intriguing, and new observations to measure metallicity of the stars and gas in the different parts of this galaxy would be a very interesting next step,” she says.

Finding Similar Galaxies

At about 718,000 light-years across, UGC 1382 is more than seven times wider than the Milky Way galaxy and, according to the study, is one of the three largest isolated disk galaxies known. The increasing availability of sensitive optical, ultraviolet, and hydrogen line observations of early-type galaxies may reveal more giant spirals like UGC 1382.

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Categories: Astronomy Headlines

40th Anniversary of Viking’s Red Planet Rendezvous

Mon, 07/18/2016 - 09:46

July 20. The date is instantly recognizable to space enthusiasts as the anniversary of the Apollo 11 Moon landing in 1969. But another major space-exploration anniversary shares the same date. Can you name which one? Perhaps if you’re a Baby Boomer.

On July 20, 1976, NASA’s Viking 1 lander touched down safely on Mars, becoming the first spacecraft to do so. The milestone was originally scheduled for July 4th, to coincide with the U.S. bicentennial celebration. But images from the Viking 1 orbiter — the lander’s mother ship — revealed the planned landing site to be more boulder-strewn than expected. It took 16 days for mission scientists to find a less hazardous alternative. Two months later, on September 3rd, the twin Viking 2 lander also made a successful touchdown.

Viking 1 Lander's first image

The first photo from the surface of Mars shows one of the Viking 1 lander’s footpads.

This past Saturday, July 16th, some 200 of the mission’s surviving scientists and engineers and their families, along with many younger space explorers inspired by the Vikings, gathered at the Wings Over the Rockies Air & Space Museum in Denver, Colorado, to celebrate the 40th anniversary of the Viking 1 landing.

The event was organized by Rachel Tillman, executive director of the Viking Mars Missions Education and Preservation Project. As the daughter of Jim Tillman, a member of Viking’s meteorology team, Rachel literally grew up with the mission and has known most of its team members — if not personally, at least by name — for nearly her entire life.

Why Denver? Because it’s home to aerospace giant Lockheed Martin, which in an earlier incarnation (as Martin Marietta) designed, built, tested, and flew the Viking landers. Mission control and the science operations center were located at the Jet Propulsion Laboratory (JPL) in Pasadena, California, which is where the action was during that historic summer of 1976 — other than on Mars itself, of course!

Celebrating Once and Future Mars Exploration

Throughout the day visitors to the museum browsed special exhibits about Viking and subsequent Mars missions. They also had the opportunity to interact one-on-one with scientists and engineers from across the country. Most of the museum’s younger visitors (and many of their parents) had never heard of Project Viking and were excited to hear stories of what it was like to be part of such an ambitious undertaking.

After the museum closed to the public, Tillman and her crew set up a lavish barbecue buffet dinner and invited several senior Vikings to offer brief reminiscences. Pat DeMartine, who developed software for the spacecrafts’ computers, recalled the team’s collective opinion that there was maybe a 50% chance that one of the two landers would make it to the surface intact. He described the fact that they both did, and then operated on Mars for several years beyond their planned 90-day lifetimes, as “spectacular, unbelievable!”

Viking Lander tools

Viking Lander on Mars.

Ben Clark, who worked on the landers’ soil-chemistry experiment, talked about the aspect of Viking that attracted the most attention from the news media and public: the search for evidence of past or present life on the Red Planet. Each lander carried three instruments designed to look for different chemical or biological signatures of living (or once-living) organisms. When the landers’ soil scoops delivered samples to the three experiments, both spacecraft produced similar results: one instrument reported a positive detection, another a negative one, and the third an ambiguous one. Clark said this lack of clear evidence for life killed NASA’s appetite for Mars exploration for the next 20 years.

Thanks to a new generation of planetary scientists and NASA leaders, Mars missions resumed in the 1990s. A fleet of increasingly sophisticated orbiters, landers, and rovers — not only from the U.S. but also from Europe, Japan, and India — have built a strong case for a warmer, wetter Mars in the past and possible seasonal flows of water in the present. Since liquid water is considered a fundamental requirement for life, interest in Mars is enjoying a tremendous resurgence, much to the aging Vikings’ delight.

Return of the Viking Interns Viking Interns

The Group 2 Viking interns, who spent July 1976 at the Jet Propulsion Lab, pose with an engineering model of the Viking Mars landers. Author Rick Fienberg is in front, second from the right, and next to him, in red pants, is Ken Carpenter.

The youngest representatives from the Viking mission at Saturday’s gala were a dozen 60-somethings who had been among the 58 undergraduate interns chosen from more than 600 applicants to spend a month at JPL during the summer of ’76. The internship program — the first of its type at NASA — was the brainchild of lander-imaging-team leader Tim Mutch of Brown University and his colleague Carl Sagan of Cornell University, who was not yet a household name (his Cosmos TV series was still four years away). Its success prompted future missions to offer similar opportunities to college students.

Many Viking interns went on to have illustrious careers in astrophysics, planetary science, aerospace engineering, and related fields. The names of quite a few of them are likely familiar to readers of Sky & Telescope. Among them:

  • Steve Albers, who in July 1991 produced what was, at the time, widely regarded as the best-ever photograph of a total solar eclipse;
  • Ken Carpenter, one of NASA’s top scientists on the Hubble Space Telescope project;
  • Andy Chaikin, who worked at S&T in the 1980s and wrote the best-selling book A Man on the Moon, which was made into an HBO mini-series;
  • Paul Spudis, a geologist at the Lunar and Planetary Institute and the world’s leading advocate of developing the Moon’s resources;
  • David Thompson, the CEO of Orbital Sciences Corp., whose Cygnus spacecraft are resupplying the International Space Station; and...
  • me! I worked at S&T for 22 years beginning in 1986, serving the last 8 as Editor in Chief, and am now the press officer for the American Astronomical Society.
Ken Carpenter and Rick Fienberg, former interns

Former Viking interns Ken Carpenter (NASA Goddard Space Flight Center) and Rick Fienberg (American Astronomical Society) at the 40th-anniversary celebration of the first Viking landing on Mars, held at the Wings Over the Rockies Air & Space Museum in Denver, Colorado.
Rick Fienberg

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Categories: Astronomy Headlines