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Next year the continental United States will experience one of nature’s greatest phenomena. August 21, 2017, will be the first time Americans on the mainland will see a total solar eclipse since 1949, and the first coast-to-coast eclipse since 1918. Such a grand spectacle is sure to garner a lot of attention, and with it comes a lot of necessary planning.Witnessing the Eclipse
A total solar eclipse happens when the Moon passes directly between Earth and the Sun. Even though the Sun is 400 times bigger than the Moon, it’s also (by cosmic coincidence) 400 times farther away. That’s why the Moon just covers the Sun. During the scant minutes of totality, dusk descends in the middle of the day. The sky darkens, animals become quiet, birds go to roost, and the temperature drops.
During totality, spectators can also see the Sun’s corona — the atmosphere composed of ionized million-degree gas. Totality is the only time when it’s safe to look at the Sun without an approved solar filter.
While I haven’t personally witnessed a total solar eclipse, I am certain it is an experience like no other. I’ve met many eclipse-chasers that have splurged hard-earned money just to stand in the Moon’s shadow for a few seconds. So I too am making plans to behold this amazing natural phenomenon — especially because it’s happening right in my backyard.Getting Ready for the Big Day
Preparing for an event this cosmic is no easy task. It’s estimated that 300 million people live within a 1- to 2-day road trip from the path of totality, where the Moon will fully cover the Sun. While that makes seeing the eclipse incredibly accessible, it also calls for a scheduling nightmare.
Already, cities are preparing for the large influx of visitors and creating destination zones where people can congregate to watch the eclipse. However, keep in mind that most of those visitors will need accommodation, considering they’re coming from distant places. Hotels are already getting booked up.
That means that if you’re interested in witnessing this event, you’d best start planning now. The sooner you plan, the more you can make out of it and the less you’ll have to stress as the day approaches.
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Feared lost for almost two years, NASA's Stereo B solar observatory is now back in (tentative) contact with mission control.
A crucial solar-monitoring asset phoned home this week, as NASA reestablished contact with the Solar Terrestrial Relations Observatory B (Stereo B). The re-connection comes after nearly two years of silence.
NASA lost contact with Stereo B on October 1, 2014. At the time, the Stereo team was preparing for a solar conjunction, when the spacecraft would pass to the other side of the Sun as seen from Earth's vantage point. To communicate with Earth, the dishes would have had to point near the Sun, so to protect the spacecraft from overheating, engineers decided to point both spacecraft away from the Sun (and Earth) and place them in safe-mode hibernation for about a year.
Before Stereo B entered safe mode, the team was testing a command loss timer — think powering your laptop off and on again — when something went wrong. Though the test went as expected, when Stereo B turned back on, its weakened signal quickly faded to silence.
But the team continued attempts to reestablish contact for the next 22 months, and on Sunday, August 21st at 6:27 p.m. EDT (10:27 UT), the Deep Space Network finally reconnected with Stereo B . This was a tentative first contact, enabling engineers to quickly assess which way the spacecraft was pointing before they turned off the high voltage transmitter to conserve power. Further checks must assess the state and health of the spacecraft before science operations can resume.
"The telemetry showed that the Inertial Measurement Unit, or IMU — which tells the spacecraft if and how fast it's rotating — failed in a way we didn't expect," says missions operations manager Dan Ossing (Johns Hopkins/Applied Physics Laboratory) in a NASA press release. "Rather than cutting out altogether, it was feeding incorrect information into the guidance and control computer."Watching the Sun in Stereo
Originally slated for a two-year mission, Stereo has exceeded expectations and duration, even if Stereo B never fully recovers. Stereo A continues to function properly.
Launched on October 26, 2006 from Cape Canaveral atop a Delta II rocket, the unique vantage points of the twin Stereo A and Stereo B spacecraft in heliocentric orbit gave solar astronomers a look at the side of the Sun the Earth doesn't see, providing stereoscopic images. Stereo A and B first reached a point 180° apart in their respective orbits, affording the first full 360° view of the Sun, on February 6, 2011.
There are no final positions for the two spacecraft: you can see the current positions of Stereo A (ahead) and Stereo B (behind) here. And like SOHO, though Stereo wasn't built to observe comets, sungrazers do occasionally photobomb its field of view:
— Alan Fitzsimmons (@FitzsimmonsAlan) August 22, 2016
Video credit: A. Fitzsimmons / Queen's University Belfast / NASA / Stereo
This isn't the longest span of time for a spacecraft to come back from the dead: a private team recovered the International Cometary Explorer/ISEE-3 mission in 2014, 15 years after it had been decommissioned.
Still, the possible return of Stereo B to action is a tremendous asset. It rejoins the Sun-watching ranks of NASA's Solar Dynamics Observatory (SDO) and Interface Region Imaging Spectrograph, the joint NASA and European Space Agency (ESA) Solar Heliospheric Observatory mission, ESA's Proba-2, and the joint Japanese Space Agency and NASA Hinode mission. This news also comes as the Sun heads toward what could be another profound minimum in its 11-year activity cycle, similar to what we saw in 2009.
Such is life with a changeable star. Here's hoping that Stereo B is once again open for business and its best days are yet to come.
You can watch the Deep Space Network live and see just which spacecraft are currently talking to Earth here.
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The discovery of trans-Neptunian object 2011 KT19 in a strange orbit deepens a key mystery in the outer solar system.
This isn't your parents solar system — or even the tidy one you memorized in primary school. In addition to the classic, orderly inner and outer planets, you can now add a bewildering menagerie of Trojans, Centaurs, Kuiper Belt objects, and more.
As a case in point, a recent discovery could hint at a distinct new class of high-inclination Centaurs lurking in the distant solar system. "Centaurs" are objects whose orbits cross those of one or more outer planets. They generally lie this side of the Kuiper belt but beyond Jupiter.
The object in question is 2011 KT19, which has now been assigned the number 471325 by the IAU's Minor Planet Center. Observers with the Mount Lemmon Catalina Sky Survey first spotted it in 2011. Then it turned up again last year in images taken with the PanSTARRS 1 telescope in Hawai'i, and a team led by Ying-Tung Chen (Academia Sinica, Taiwan) derived the object's orbit and announced its findings this month.
And what a strange new world this is. It currently shines at a faint apparent magnitude of 22 in the constellation Serpens Caput, near its border with Libra. Based on reasonable guesses for its albedo (surface reflectivity), 2011 KT19 should be 70 to 200 km in diameter. Even on the high end of this range, the tiny world is only one-sixth the diameter of Pluto's large moon Charon.
But it's the bizarre orbit of 2011 KT19 that gives astronomers pause: perihelion (reached in 1999) is 23.8 astronomical units from the Sun, aphelion is 47.4 a.u., and one orbit takes some 212 years to complete. This takes it inside the orbit of Neptune, and out to just inside the aphelion of Pluto. The inclination of 2011 KT19's orbit to the ecliptic is a whopping 110°, meaning that it orbits the Sun in a slow retrograde orbit — one moving "backward" with respect to the motion of the major planets. Chen nicknamed this contrarian object "Niku," a Chinese adjective meaning "rebellious."
“We identified Niku in our searches for outer solar system objects in the PanSTARRS1 data,” says collaborator Matthew Holman (Harvard-Center for Astrophysics). “After we reported our observations to the Minor Planet Center, they were linked to 2011 KT19, which had been observed over a span of just 8 days, not long enough to recognize its unusual orbit.”
Followup observations were carried out by the Lulin Observatory in Taiwan, and archived observations were taken from the Canada-France-Hawaii Telescope (CFHT) observatory and the Dark Energy Camera based at the Cerro Tololo Inter-American Observatory in Chile.Rebellious Rocks
Just one other trans-Neptunian object is known to have a retrograde orbit: 2008 KV42, (informally named "Drac," for Count Dracula) follows a path inclined 103° relative to the ecliptic. These two objects — along with four other small Centaur asteroids in prograde orbits — share a common orbital plane. Moreover, the two retrograde objects have nearly identical ascending nodes, as do the four prograde objects. After looking at one million orbital simulations, Chen's team concludes that the likelihood of getting all six objects in the same orbital plane is 1 in 6,250 (0.016%).
“The most interesting thing is that there appears to be a group of objects like Niku that share the same orbital plane, roughly perpendicular to the plane of the solar system,” says Holman. “Even stranger, some of the objects are prograde and some are retrograde.”
The team notes that this coincidental alignment isn't stable — the simulations show that natural orbital precession should scatter such objects over just a few million years, a relatively short span of time in the history of the solar system. At this point, just what sort of mechanism is keeping these high inclination orbits in the same common plane isn't known.
Chen's team notes that the "Planet Nine" simulations run by Caltech astronomers Mike Brown and Konstantin Batygin yield an X-shaped cluster of high-inclination objects in two common orbital planes, though neither are coincident with the observed orbits of these high inclination TNOs.
The object hypothesized by Brown and Batygin should have 2 to 4 Earth masses but occupy a much more distant orbit with an estimated semimajor axis of around 700 a.u. This kind of distant, massive perturber can't exert enough gravitational influence to confine the six orbits of 2011 KT19 and its ilk. And a big, massive "something" closer in would stir up trouble in the Kuiper Belt.
"The orbit is what's truly exciting about this new body," Batygin said in a recent PRI Science Friday interview. “We don't really have a mechanism to explain these types of orbits.”
Do more renegade TNOs exist? Are these captured asteroids from a more distant reservoir of Kuiper Belt objects? Successor surveys, such as Large Synoptic Survey Telescope (LSST) set to go online in 2019 mightreveal if Niku, Drac and friends have any company in the outer solar system — and just what might be maintaining their common orbits.
It's a brave new solar system indeed, one that doesn't always want to conform with last year's textbooks.
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Astro-Physics announces the Quad Telecompressor Corrector ($1,520) for its 130 StarFire GTX and EDFGT telescopes. This large-format 0.72x reducer shortens the focal length of the 130-mm f/6.3 StarFire GTX from 819 to 598 mm (f/4.6), allowing you to record wider expanses of the sky. The four-element Quad TCC fits into the scope's 3.5-inch focuser, producing pinpoint stars across the entire field of a 35-mm sensor, and also works with Telescope Engineering Company (TEC) refractors with additional spacers offered by Astro-Physics.
SkyandTelescope.com's New Product Showcase is a reader service featuring innovative equipment and software of interest to amateur astronomers. The descriptions are based largely on information supplied by the manufacturers or distributors. Sky & Telescope assumes no responsibility for the accuracy of vendors statements. For further information contact the manufacturer or distributor. Announcements should be sent to nps@SkyandTelescope.com. Not all announcements will be listed.
Living in voids might be tangentially responsible for three small galaxies’ recent flurries of starbirth.
Dwarf galaxies are galactic runts. They can be a thousandth (give or take a factor of 10) as massive as our galaxy, the Milky Way. Because they’re so small, they’re sometimes their own worst enemies: if a few supernovae go off inside, the blasts can expel all the dwarf’s gas, stifling star formation until the gas can cool and rain back down — if it ever does.
Two different teams have now found dwarf galaxies with ramped-up star formation, giving us a look at what triggers starbirth in these little systems. But what makes these particular dwarfs neat is that they might be in their current state thanks to voids, the gaps in the cosmic web of galaxies that make the large-scale universe look like a sponge.
Coming in from the Void?
Erik Tollerud (Space Telescope Science Institute) and colleagues used Hubble to spot two tiny dwarfs, called Pisces A and B. They lie about 20 and 30 million light-years away, respectively, beyond the Local Group of stellar metropolises that cluster around the Milky Way and Andromeda galaxies.
Pisces A and B are puny, each only a couple thousand light-years across. They don’t have many stars, either — each holds on the order of 10 million suns. For comparison, the Milky Way contains approximately 100 billion stars, and its disk spans more than 100,000 light-years. So these dwarfs are basically faint, sparse clouds of stars held together by dark matter.
The team’s observations reveal that Pisces A and B lie on the edge of a nearby cosmic desert called the Local Void. Each dwarf also boasts a couple dozen young, blue stars. In fact it looks like the galaxies both experienced upticks in their star production within the last 300 million years.
One explanation for the bevies of beautiful stars is that their births were triggered by the dwarfs’ migration through space: perhaps they recently left the Local Void and entered the strand of the cosmic web they’re now in. More gas floats around in the web’s filaments and sheets than in the voids, and as a galaxy entered a strand, the pressure of ramming into this ambient stuff could compress the gas inside the galaxies, triggering star formation. Indeed, several astronomers have suggested that this process could kick start starbirth or even kill it by tearing the gas out of a galaxy.
But as the team explains in the Astrophysical Journal, it hasn’t measured the dwarfs’ motions — the researchers only know the locations of Pisces A and B, not where they’re coming from or where they’re going. The idea that their star formation is being spurred on by entering the web is only an extrapolation based on where the dwarfs currently lie.
Tollerud acknowledges that the star formation might be internally triggered, by the cooling and raining-down process I described earlier. But dwarfs are notoriously on-again-off-again in their star formation, and the astronomers originally found these galaxies by looking for clumps of gas, not stars — so they didn’t discover Pisces A and B because of the burst of starbirth. “It would seem like quite the luck that the only two we found happen to be the ones that are in their uptick right now,” he says.
Fleas on Fleas
A different dwarf galaxy with the stirring name DDO 68 definitely lies in a void — the Lynx-Cancer void, roughly a third of the way around the sky from Pisces A and B. DDO 68 lies about 40 million light-years away. Its gas is incredibly pristine, barely tainted by the heavier elements created in stars. It’s also distorted, with a curving tail that kind of makes it look like a fried jumbo shrimp.
Thanks to its oddball shape and tail, which contains stars of all ages, astronomers already suspected that DDO 68 has been tidally pulled on, or even merged with, one or more dwarfs. Francesca Annibali (INAF-Bologna Observatory, Italy) and colleagues decided to look more carefully using both Hubble and the Large Binocular Telescope, the latter of which has a much wider field of view than Hubble and can thus more easily reveal substructures.
As reported in the August 1st Astrophysical Journal Letters, the team found an arc and at least one notable stream of stars near the galaxy’s edges. Stars in the arc have all sorts of ages, but some are as young as 50 million years old — astronomically speaking, they were born yesterday. The stream’s stars are older, at least 2 billion years old.
Based on computer simulations, the team thinks that DDO 68’s harried look could be the result of eating two, even smaller dwarfs. Although voids are supposedly empty, the term “void” can be misleading, Annibali explains. By definition they’re bereft of big, bright galaxies, but little galaxies sometimes live in them.
Plus, she adds, astronomers expect galaxies to live in associations, with dwarfs hosting their own satellites. Such a miniature clique wouldn’t survive long near a massive galaxy like the Milky Way — and there are hints that some of the satellites our galaxy is munching on began life together in groups — but it could survive for much longer in a void, she says.
But it’s unclear whether these structures really are from smaller galaxies that DDO 68 is eating, Tollerud cautions. Dwarfs often have weird shapes, even in the absence of interactions, or maybe the galaxy ate a star cluster. We need higher-resolution images to reveal what these truly features are, he says.
E. J. Tollerud et al. “HST Imaging of the Local Volume Dwarf Galaxies Pisces A & B: Prototypes for Local Group Dwarfs.” Astrophysical Journal. August 20, 2016. STScI press release.
F. Annibali et al. “DDO 68: A Flea with Smaller Fleas that on Him Prey.” Astrophysical Journal Letters. August 1, 2016. LBTO press release.
Fly through the cosmos with NASA JPL's iconic "Visions of the Future" posters.
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New Horizons' flight past Pluto last year revealed a stunning world we couldn't have dreamed up — now scientists are sifting through the data, trying to make sense of this frozen wonderland. A little closer to home, ExoMars is due to arrive at the Red Planet by September. It will be the first probe to carry instruments specifically designed to search for signs of life on a world that still holds its own fair share of secrets. And a bit farther afield (7,500 light-years or so from Earth), astronomers are finally beginning to get a handle on Eta Carinae, the supernova that wasn't. Meanwhile, while Pluto and Mars may not be at their best this October, the others beckon: Saturn, Venus, Uranus, and Neptune, to name a few, as well as treasures held in the celestial Swan.Feature Articles
New Horizons I: Pluto's Amazing Story
This distant world bristles with geologic diversity unmatched in the outer solar system.
By J. Kelly Beatty
Looking for Life on Mars
The first phase of the ExoMars mission arrives at the Red Planet this month to search for evidence of past or present life.
By Camille M. Carlisle
What Caused the Great Eruption?
New theories and observations are helping astronomers solve the mystery of Eta Carinae's 19th-century explosion.
By Keith Cooper
The Backyard Sky: Fall
Say goodbye to summer with these seasonal sights.
By Rod Mollise
George Willis Ritchey's Great Adventure
The world's giant telescopes today owe their optical design to a star-crossed, obsessive genius.
By Ted Rafferty
Watch the newest ideas about how this star exploded unfold in 3D.
Light Pollution Report
Read the latest on the status of light pollution around the globe.
LISA Pathfinder Surpasses Expectations
Successful first results pave the way for a future space-based gravitational wave detector.
Librations and other lunar data for October 2016.
Tower of Light
Saturn, Venus, and Antares fall into line near the end of October.
By Fred Schaaf
Moon, Aldebaran Meet Again
This time, a grazing occultation crosses Los Angeles and Denver.
By Alan MacRobert
The Celestial Swan
October's familiar skies contain a wealth of fresh sights.
By Sue French
S&T Test Report: Video Astronomy with the Atik Infinity
Atik brings video observing fully into the digital age.
By Rod Mollise
Table of Contents
See what else October's issue has to offer.
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