Astronomy & Science

Join Alan Stern in S&T‘s Next Live Webinar!

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No matter what your level of interest in planetary exploration, you won't want to miss S&T's live webinar on Saturday, January 28th. Hear Alan Stern's personal take on how NASA's New Horizons spacecraft got to Pluto and what we learned once it got there.

The late astronomer Carl Sagan was fond of saying that ours is the only generation that will explore the solar system for the first time. Adopting a generously broad definition for "generation," arguably the most-awaited of these explorations occurred in July 2015, when NASA's New Horizons spacecraft swept past Pluto and its family of moons.

Alan Stern with Pluto bumper sticker

Alan Stern, principal investigator for NASA's New Horizons mission, holds up a bumper sticker during a science update 10 days after the spacecraft's historic flyby.
NASA / Joel Kowsky

During that flyby, the spacecraft revealed worlds far more complex and amazing than anyone had imagined. In fact, it took three feature articles in Sky & Telescope (the October, November, and December 2016 issues) to lay out all the discoveries made.

No one has a better handle on the 25-year-long effort to reach this distant planetary outpost, and what we learned once arriving there, than Alan Stern. In his three decades of academic research, Stern has focused on studies of our solar system's Kuiper Belt and Oort cloud, comets, outer-planet satellites, the Pluto system, and evidence of solar systems around other stars. He even had a stint as the NASA Associate Administrator in charge of space science.

Pluto in false color

Four images from New Horizons’ Long Range Reconnaissance Imager (LORRI) were combined with color data from the Ralph instrument to create this enhanced color global view of Pluto. Rectangles indicate the areas seen in greater detail.

Clyde Tombaugh might have discovered this far-flung world, but it's Stern who'll be forever remembered as the Guy Who Got Us to Pluto. He and his team overcame many obstacles in getting New Horizons approved, built, launched, and delivered to its primary destination more 3 billion miles away.

So here's you chance to spend a vicarious hour with Stern, during the next Sky & Telescope live webinar on Saturday, January 28th, at 12:00 p.m. (noon) Eastern Standard Time. In his presentation, Stern will tell us all about New Horizons — from its inception to planning its historic flyby to the jaw-dropping discoveries it made. This is one you don't want to miss.

Click here now to register to attend.

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The Incredible Skies of Namibia

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S&T Contributing editor Govert Schilling explores two unique astronomical sites that lie under the dark skies of Namibia.

It's one of the strangest things I've ever seen. All around me is a flat area of loose rocks and small, thorny vegetation. But there's no horizon. No endless plains, no distant mountains. The scene suddenly stops at a distance of a few hundred meters. Beyond and above is just blue sky, with a burning hot Sun. I feel like I'm on a mini-planet.

Gamsberg summit

The flat, rocky summit of Namibia's Gamsberg.
Govert Schilling

"Pretty weird, isn't it?" says Waltraub Eppelmann. We're at the center of the flat summit of Gamsberg, at 2,347 meters the third-highest mountain in Namibia (a former German colony). Waltraub drove me up here in her 4WD Toyota Landcruiser. It was a two-hour spine-chilling trip on the worst "road" I've ever been on, basically a jumble of large rocks and boulders, with fathomless abysses and grades up to almost 45 degrees.

From the incredibly steep edge of the plateau, which measures some 1,000 by 800 meters, the view across the Hakos mountain range and the Khomas highland is spectacular. I try to imagine how Gamsberg will look like a few years from now, when construction of the Africa Millimetre Telescope (AMT) may have started.

A team led by Heino Falcke (Radboud University, The Netherlands), has recently signed an agreement with the University of Namibia to start developing the 15-meter single-dish AMT on the "mini-planet" summit of Gamsberg.

The main goal of the AMT is to take part in the international Event Horizon Telescope experiment — a network of millimeter-wave radio dishes around the world that should soon be able to image the supermassive black hole in the center of our Milky Way galaxy. Preferably, Falcke explains, the individual telescopes would be distributed evenly across the globe, "and there's a big hole on the map in Africa."

That’s still largely in the future. Right now, the Gamsberg only holds a slender telecommunications tower and a few small buildings operated by the International Amateur Observatory. "Things will change," says Waltraub Eppelmann. For one, the drive to the plateau will no longer be an adrenalin-producing tourist attraction once the AMT project constructs a proper access road to the summit.

From Farm to Observatory Hakos Guestfarm

The Hakos Guestfarm welcomes amateur astronomers to one of the darkest sites
in the world.
Hakos Guestfarm

Together with her husband Friedhelm Hund, Waltraub runs the nearby Hakos Guestfarm. In the early 1970s, her father Walter Straube, who died in 2015, offered his cattle farm as a base for astronomers from the Max Planck Institute for Astronomy in Heidelberg, Germany. In 1970, the institute had bought the Gamsberg summit with the goal of putting a 2.2-meter optical telescope there, but this telescope eventually ended up at the European La Silla Observatory in northern Chile, leaving Gamsberg undeveloped.

Nevertheless, the extremely clear and dark skies above this part of southern Africa attracted semi-professional amateur astronomers. Famous German astrophotographer Hans Vehrenberg — a lawyer by profession — built a small observatory at Straube's farm, and became like a second father to young Waltraub and her brother Siegfried. After Vehrenberg's death in 1991, Hakos turned into an astronomical oasis for adventurous travelers, with guest rooms, camp sites, great food, some nice telescopes, and magnificent skies.

Meanwhile, the dark skies of Namibia kept luring professional astronomers too. Just after the turn of the century, not far from the Hakos farm, the Max Planck Institute started construction of the High Energy Stereoscopic System (HESS), named in part to honor the Austrian physicist and Nobel laureate Victor Hess, who discovered cosmic rays in 1912. HESS can just be glimpsed from the 350-kilometer gravel road between Namibia's capital city, Windhoek, and the harbor town of Walvis Bay. The unique telescope array is providing a view into the energetic universe.

HESS telescope array

Overview of the HESS Observatory. The five 'telescopes' are surrounded
by lightning rods.
University of Heidelberg

Every clear and hour of the night, the HESS telescopes are on the lookout for brief flashes of Cherenkov radiation — an extremely faint, bluish glow generated when high-energy gamma-ray photons from deep space enter Earth's atmosphere. Each HESS reflector consists of hundreds of flat mirrors, concentrating the faint flashes on an array of sensitive photo detectors. Four 12-meter reflectors, each with 382 circular 60-centimeter mirrors, are arranged in a square with sides of 120 meters; a fifth 28-meter dish, with 875 hexagonal 90-centimeter mirrors, was added five years ago in the square's center.

The observatory has detected energetic outbursts from quasars and galactic pulsars, which released photons with incredible TeV (tera-electronvolt) energies. HESS has also studied gamma rays produced in particle acceleration processes occuring at supernova shock waves. Moreover, the instrument observed very high-energy gamma rays from the galactic center, the origin of which is still being debated. The HESS website highlights other science results over the past decade.

Uncertain Future HESS Telescope

One of the four 12-meter 'light bucket' telescopes of the HESS
Observatory. The huge parabolic reflector consists of dozens of individual
flat, circular mirrors.
Govert Schilling

As I tour the photogenic site, French and South African technicians are carrying out maintenance on the large camera of the 28-meter instrument.

“We were in the race to host the Southern-Hemisphere part of the future (much bigger) international Cherenkov Telescope Array,” says site manager Toni Hanke, “but this will now be constructed at the European Paranal Observatory in Chile.”

“I'm not really sure about the future of HESS,” he adds. “It would be sad to dismantle this pioneering observatory because of lack of funding."

Then again, with the development of the AMT nearby, Waltraub's Hakos Guestfarm may start to draw even more dedicated amateur astronomers. I, for one, surely hope to return here someday.

Sky & Telescope contributing editor Govert Schilling spent six weeks in southern Africa in the fall of 2016. In a series of blog posts, he writes about the astronomical highlights of his trip.

The post The Incredible Skies of Namibia appeared first on Sky & Telescope.

This Week’s Sky at a Glance, January 20 – 28

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Venus and Mars at nightfall, late January 2016

Mars and Venus have been creeping closer together for months, and this week they close from 7° to 6° apart. But they're not going to pass each other. They'll be closest, 5½° apart, in early February, and then Venus will begin to drop back down and away.

Friday, January 20

• After dinnertime, the bright, equilateral Winter Triangle glitters in the southeast. Sirius is its lowest and brightest star. Betelgeuse stands above Sirius by about two fists at arm's length. To the left of their midpoint is Procyon.

• Vesta, the brightest asteroid, is magnitude 6.2 this week. It's just past opposition, looping high near Castor and Pollux. Binoculars will show it; see article and finder chart.

Saturday, January 21

• Is your sky dark enough for you to see the winter Milky Way? After dinnertime it runs vertically up and across the zenith: from Canis Major low in the southeast, up between Orion and Gemini, through Auriga and Perseus almost straight overhead, and down through Cassiopeia, Cepheus, and Cygnus to the northwest horizon.

• Early in the dawn of Sunday the 22nd, spot the waning crescent Moon hanging in the southeastern sky. Some 12° below it (for North America) is Antares. Look 15° to the left or lower left of Antares for Saturn. The same distance lower left of Saturn is Mercury.

Sunday, January 22

• Zero-magnitude Capella high overhead, and equally bright Rigel in Orion's foot, are at almost the same right ascension. This means they cross your sky’s meridian at almost exactly the same time: around 9 p.m. now, depending on how far east or west you live in your time zone. (Capella goes exactly through the zenith if you're at latitude 46° north: Portland, Oregon; Montreal; central France.) So, whenever Capella passes its very highest, Rigel always marks true south over your landscape. And vice versa.

Moon, Antares, Saturn, and Mercury at dawn, Jan. 23-26, 2017

The waning Moon steps downward above Antares, Saturn, and Mercury in the dawn.

Monday, January 23

• In early dawn Tuesday morning the 24th, look southeast for the waning crescent Moon hanging 3° upper left of Saturn (when seen by North America), as shown here.

Tuesday, January 24

• As dawn brightens on Wednesday morning the 25th, look very low in the southeast for the thin waning crescent Moon, as shown here. Saturn is about 14° to the upper right of it (for North America). Little Mercury is about 6° below the Moon. Binoculars will help, especially as dawn grows brighter.

Wednesday, January 25

• Sirius twinkles brightly after dinnertime below Orion in the southeast. Around 8 p.m., depending on your location, Sirius shines precisely below Betelgeuse in Orion's shoulder. How accurately can you time this event for your location, perhaps using a plumb bob or the vertical edge of a building? Of the two, Sirius leads early in the evening; Betelgeuse leads later.

Thursday, January 26

• Right after dark this week, face east and look very high, almost overhead. The bright star there is Capella, the Goat Star. To the right of it, by a couple of finger-widths at arm's length, is a small, narrow triangle of 3rd and 4th magnitude stars known as "the Kids." Although they're not exactly eye-grabbing, they form a never-forgotten asterism with Capella.

Friday, January 27

• The sky's biggest asterism (informal star pattern) — at least the biggest that's widely recognized — is the Winter Hexagon. It now fills the sky toward the east and south after dinnertime. Start with brilliant Sirius at its bottom. Going clockwise from there, march through Procyon, Pollux and Castor, Menkalinan and Capella very high, Aldebaran over to
Capella's lower right, down to Rigel in Orion's foot, and back to Sirius.

Betelgeuse shines inside the Hexagon, off center.

• New Moon (exact at 7:07 p.m. EST).

Saturday, January 28

• After dark now the Great Square of Pegasus is sinking down in the west, tipped onto one corner to the right or upper right of Venus and Mars. Meanwhile the Big Dipper is creeping up in the north-northeast, tipped up on its handle.


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

Mercury and Saturn are low in the southeast in early dawn. But Mercury (magnitude –0.2) is sinking lower every day, while Saturn (magnitude +0.5) is moving higher into much better view to Mercury's upper right. They widen from 14° to 22° apart this week.

Antares, magnitude +1.0, twinkles 15° to Saturn's right or upper right. The waning crescent Moon passes through this area on the mornings of January 23rd through 26th, as shown above.

Venus is the brilliant "Evening Star" this winter, high in the southwest during twilight and long after. It's currently magnitude –4.7, between Aquarius and Pisces. To its upper left you'll spot Mars, an orange less than 1% as bright.

In a telescope Venus is now slightly less than half sunlit. It's growing larger as it approaches us, now about 28 arcseconds from cusp to cusp. For the rest of the winter, Venus will continue to enlarge as its phase wanes down to a thin crescent.

Venus in a telescope is least glary when viewed in bright twilight. So get your scope on it as soon as you can see it naked-eye.

Mars (magnitude +1.1) is the fainter "star" upper left of Venus. The separation between them shrinks from 7° to 6° this week. In a telescope Mars is just a tiny fuzzblob 5 arcseconds wide.

Vesta, just past opposition, is a very accessible magnitude 6.2. Article and finder chart.

Jupiter on Jan. 12, 2017

Jupiter's Great Red Spot side on January 12th, imaged by Christopher Go. Upper left of the Great Red Spot, the small, pale-orange Oval BA has just crossed the central meridian. South is up. In the northern hemisphere, the North Equatorial Belt and North Temperate Belt have almost blended to become one very wide belt.

Jupiter (magnitude –2.1, in Virgo) rises around 11 or midnight and shines brightly high in the south before the first light of dawn. Spica dangles 3½° below or lower right of it. Jupiter is creamy white; Spica is an icier shade of white with a trace of blue (once it's fairly high up).

In a telescope Jupiter is 38 arcseconds in diameter, on its way to 44 arcseconds for late March through April. (Opposition is April 7th.)

Uranus (magnitude 5.8, in Pisces) is still high in the southwest right after dark.

Neptune (magnitude 7.9, in Aquarius) is getting low in the west-southwest right after the end of twilight. Finder charts for Uranus and Neptune.


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 Standard Time (EST) is Universal Time (UT, UTC, or GMT) minus 5 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, January 20 – 28 appeared first on Sky & Telescope.

Brunswick Astronomy Club

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Brunswick Astronomy Club


2787 Michael Drive
Brunswick, OH  44212


Allan Cook








The Brunswick Astronomy Club is a non-profit, educational organization established in 1991. Our goal is to bring, both novice and advanced, amateur astronomers together in the excitement of exploring and enjoying our universe.

The post Brunswick Astronomy Club appeared first on Sky & Telescope.

Stellar Streams in the Milky Way Halo (A Gallery)

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Streams of stars abound in the Milky Way halo, as discussed in the April 2017 issue of Sky & Telescope. They are the remains of dwarf galaxies that once orbited the Milky Way, passed by too closely, and tore apart in our galaxy's gravitational well. We showcase here additional stunning images of these galactic ghosts.

Sagittarius Stream as seen on the sky

This map of the sky shows the stars that are part of the Sagittarius streams, as imaged by the SDSS, against a backdrop of the galactic plane, which the SDSS largely avoids. The stars' colors indicate their distances — blue marks nearby stars while red marks stars farther away. The dotted red lines trace out the Sagittarius streams as they disappear behind the galaxy from our viewpoint. The blue ellipses in the center show the current location of what remains of the Sagittarius Dwarf Galaxy on the far side of the galaxy from us.
S. Koposov / SDSS-III collaboration

Sagittarius Stream

This artist's conception illustrates the geometry of the tidal tails of stars (white) streaming from the Sagittarius Dwarf Galaxy (orange) that orbits the Milky Way. The bright yellow circle to the right of the galaxy's center is our Sun (not to scale). Sagittarius is on the other side of the galaxy from us, but we can see its tidal tails of stars stretching across the sky as they wrap around our galaxy.
Amanda Smith / University of Cambridge

NGC 5907 and stellar stream loops

Such looping stellar streams, the results of "collisions" with minor galaxies, are common in other nearby spirals too, such as these loops around NGC 5907 (seen edge-on).
R. J. Gabany in collaboration with Martínez-Delgado et al. (2010)

Whale galaxy, NGC 4631

Simulations can provide insight into the origin of observed stellar streams, such as this stream observed around the Whale Galaxy, also known as NGC 4631 (left). The simulation of a satellite galaxy disrupted by its larger companion's gravity 3.5 billion years ago, reproduces the observed stream (right).
Martinez-Delgado et al. 2015

Visit R. Jay GaBany's website for a closer look at many other tidal streams around nearby spiral galaxies.

And just for fun, peruse the Victorian-era spirit photography that served as inspiration for this article, provided by the National Media Museum in the UK.

The post Stellar Streams in the Milky Way Halo (A Gallery) appeared first on Sky & Telescope.

Tracking Down the Milky Way’s Most Distant Stars

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The most distant stars discovered in the Milky Way might have been ripped away from a companion galaxy.

view of Milky Way from ULAS J0744+25

This illustration demonstrates how small the Milky Way would look from the location of ULAS J0744+25, a red giant star nearly 775,000 light-years away.
Visualization Software: Uniview by SCISS; Data: SOHO (ESA & NASA) / John Bochanski (Haverford College) / Jackie Faherty (AMNH and Carnegie Institute's Department of Terrestrial Magnetism)

Over the last decade, multiple groups of astronomers have identified luminous stars more than 300,000 light-years from Earth. I was fortunate enough to discover the most distant of these stars, cool red giants that are almost 900,000 light-years away — the most distant stars that are still bound to our galaxy. (The galaxy's stellar disk, for comparison, is only 100,000 light-years across. Our galaxy's dark matter halo extends up to ten times farther, out to 1 million light-years.)

When my group at Rider University first published our findings, we speculated on just how those stars could have gotten so far away. Perhaps a gravitational interaction had ejected them from the Milky Way’s disk, maybe they were the brightest members of a dark companion dwarf galaxy, or they could even the remnants of a long-forgotten galaxy shredded by the Milky Way’s gravity.

Now, in a result accepted for publication in the Astrophysical Journal (available online here), Marion Dierickx and Avi Loeb (both at Harvard University) argue that the last scenario seems most likely: some of these stars are probably members of what was once the Sagittarius dwarf galaxy.

Sagittarius Stream

This artist's impression shows the tidal tails of stars (white) streaming from the Sagittarius Dwarf Galaxy (orange) that orbits the Milky Way. The bright yellow circle to the right of the galaxy's center is our Sun (not to scale). Sagittarius is on the other side of the galaxy from us, but we can see its tidal tails of stars stretching across the sky as they wrap around our galaxy.
Amanda Smith / University of Cambridge

Sagittarius is the best-studied dwarf galaxy remnant in our galaxy. This small galaxy passes close by the Milky Way in its orbit and every time it sweeps by, it sheds stars. The streams of stars loop around our galaxy in majestic curves that crisscross over the sky. Steve Majewski and collaborators first mapped the galaxy’s remnants using cool red giants identified in 2MASS observations. Further observations using the Sloan Digital Sky Survey refined the position, distances, and velocities of these stars.

Starting with these maps, Dierickx and Loeb wound the computational clock backwards to more than 8 billion years ago, when Sagittarius would first have started interacting with the Milky Way. Then they varied the initial velocity and direction of the dwarf galaxy in their simulation. "The starting speed and approach angle have a big effect on the orbit, just like the speed and angle of a missile launch affects its trajectory," Loeb explains. Watch the animation here.

Then they let the simulations run and compared their results to the 11 most distant stars identified in the Milky Way. Five of these stars matched the positions, velocities, and distances expected for Sagittarius members at very large distances. The other six might be members of another former dwarf galaxy, but this is less certain.

"More interlopers from Sagittarius are out there just waiting to be found," Dierickx says.

As a researcher searching for distant stars, I find the work by Dierickx and Loeb to be very exciting. It confirms the existence of these stars at large distances, and it gives observers a map to finding more. I hope that we will have many more stellar discoveries in the coming years.

The post Tracking Down the Milky Way’s Most Distant Stars appeared first on Sky & Telescope.

Vesta, Brightest Asteroid, Now High Overhead

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Vesta is at opposition, shining at 6th magnitude in Gemini as it awaits your binoculars or small scope.

The first asteroid discovered, 1 Ceres, is still the biggest. But it's not the brightest. That honor goes to 4 Vesta, at least during the weeks around its times of opposition. Which means now.

Vesta in Gemini, early 2017

Vesta spends winter and early spring looping near the heads of the Gemini twins.

This week Vesta shines an an inviting magnitude 6.2. It's conveniently located near Gemini's Pollux and Castor, which climb high up the eastern sky as evening grows late. Small binoculars will do the trick, if you have the charts here and know how to use them.

The chart above shows the whole Gemini constellation. Gemini is located left of Orion after dinnertime, and upper left of Orion as the evening draws toward midnight. The black box shows the area of the second, closer-up chart below.

Finder chart for Vesta in early 2017

Vesta's path, with ticks showing its position at at 0:00 Universal Time every three days. Click for printable version.

Here Vesta's position is marked with a tick at 0:00 Universal Time every three days. For North America, this time falls in the early evening (or late afternoon) or the previous date. Put a pencil dot on Vesta's position for the evening when you'll go looking.

Click for a black-on-white version to print and take with you out into the night.

Outdoors, your starting point is Pollux. Note the pattern of the brightest stars around it. The closeup chart is 9° tall, nearly a fist-width at arm's lengths when you're viewing with the naked eye. In binoculars or a finderscope you see a somewhat smaller view, typically 5° or 6° tall. Bear this in mind when comparing.

North on the chart is up; north in the sky is always the direction toward Polaris. Turn the chart around to match.

Now, comparing the chart to your magnified view, use patterns of stars — triangles, rectangles, kite shapes — to work your way from Pollux to the asteroid's position.

At 6th magnitude, Vesta is fainter than the stars connected with purple lines to form the Gemini stick figure, but it's not nearly as faint as the tiniest stars shown. See the magnitude scale on the left.

In the coming weeks and months Vesta will fade into the distance, and you'll need more of those fainter stars. It will still be magnitude 6.5 on February 1st but 7.0 on March 1st and 7.6 on April 1st.

Vesta is one of the few asteroids that's been visited by a spacecraft. As seen in the image below from NASA's Dawn mission, it's a heavily cratered, somewhat oblong body of a lighter gray shade than most asteroids, which tend toward very dark brown or almost black. Explore in more detail, and reflect on the fact that this is the same tiny point you can locate yourself over your roof or treetops.

Vesta from Dawn

Full Vesta. It's 355 miles (570 kilometers) from end to end. This composite was assembled from images by the Dawn spacecraft orbiting it in 2011.

The post Vesta, Brightest Asteroid, Now High Overhead appeared first on Sky & Telescope.

See Mercury First, Then Have Breakfast

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Late sunrises make it easy to follow the parade of planets at dawn, including a nice apparition of Mercury this week and three successive lunar conjunctions.

Near and Far Planets Draw Close

Planets Mercury and Saturn make a pretty pair at dawn in the southeastern sky this month. You can spot them an hour before sunrise. This photo was taken on January 15th from Duluth, Minnesota.
Bob King

Before you know it, the Sun will come up at 5 a.m., making observing at dawn a serious loss-of-sleep experience. Now's the time to take advantage of winter's late sunrises — typically around 7:30 a.m. — to get out and look at your favorite planets or the Moon before a final cup of coffee and off to work.

The Moon slims to last-quarter phase this week and passes just 2.5° north of Jupiter on Thursday morning, January 19th. Few of us stay up late enough for a good look at the last-quarter Moon, when craters and hills cast their shadows to lunar east instead of west. After you've grown accustomed to first-quarter phase, seeing shading in reverse can be pleasantly disorienting.

Then there's the Jovian weather. A bright plume around longitude 190° (CM2) has recently appeared in the South Equatorial Belt (SEB), marking the start of a new SEB outbreak. Is the Great Red Spot still shrinking? Find out yourself Thursday morning, when it rotates squarely into view around 6:30 a.m. CST (7:30 EST, 5:30 MST, and 4:30 PST).

If all that doesn't entice you to drag out the scope, there's also this other little thing happening — Mercury's greatest western elongation.

The little planet with the big iron heart is having a decent morning apparition, reaching its greatest apparent distance west of the Sun on the 19th, the very same morning Jupiter, Spica, and the third-quarter Moon gather in conjunction high in the southern sky at dawn.

Steppingstones to Mercury

Use this map, set for 40° N latitude on January 19th, to navigate from Antares in Scorpius to Saturn, and from there to Mercury.
Map: Bob King, Source: Stellarium

When it comes to finding Mercury, Saturn gladly lends a hand. Like Mercury, the ringed planet recently made its dawn debut after solar conjunction. Saturn, being an outer planet, gradually rises into a dark sky, while little Mercury remains closely tethered to the Sun. Catch it now, when it's tugging at the end of its leash before Sol yanks it back into the searing light of day.

Saturn rises at 5:00 a.m., but isn't an easy catch until around 6:15–6:30 a.m., when dawn blues up the eastern sky. Look for it some 10°–15° high in the southeast, a fist and a half lower left of ruddy Antares in Scorpius. Once you've located Saturn, Mercury's a snap, provided you have a good horizon. Look about one fist to the lower left (farther east) of Saturn for a similarly bright star about an hour before sunrise. Yep, that's Mercury!

Littlest Planet Fills Out

Like Venus, which also orbits the Sun interior to the Earth, Mercury displays phases. In the next two weeks, the planet will gradually fill out and brighten.
Diagram: Bob King, Source: Stellarium

Both planets currently shine around magnitude +0.6. I easily found Saturn from my observing site at +47° N on the 15th around 6:20 but had to wait until 6:45 (an hour before local sunrise) for Mercury to clear a line of distant trees. Both planets were obvious with the naked eye up till about 45 minutes before sunrise.

The duo was closest earlier this month with a minimum separation of about 7°. Since then, Saturn's hurried along to the west, a consequence of Earth's revolution around the Sun, with Mercury trying its best to catch up, ultimately an impossible task. They're currently 12° apart with their separation widening a degree a day until Mercury disappears in the solar glow in early February. That leaves about two weeks to catch this fleetest of planets before it reaches superior conjunction with the Sun in early March. After its solar baptism, Mercury will slip into the evening sky and put on a great show in late March–early April.

Moon Makes for Pretty Pairings

The Moon pairs up with Saturn and then Mercury next week on January 24–25. If it's clear, consider taking a photo the trio. You'll find hints on to do it below. Mercury's travels away from and back toward the Sun in January–early February are depicted in the loop at lower left.
Map: Bob King, Source: Stellarium

But I'm getting ahead of myself. Be sure to mark your calendar for one week from now. On January 24th, the waning crescent Moon, just a few days before new, slices the evening sky next to Saturn. And on January 25th, the Moon glides some 5° north of Mercury. You may even want to take a picture of these conjunctions. To do so, you'll need a tripod and camera that can take a short time exposure. Use manual mode, focus on the lunar crescent, frame a scene, set the ISO or sensitivity to 400, set the lens aperture to f/4, and expose for 2–5 seconds.

Few people ever get to see Mercury because it requires a deliberate effort to track it down. Once you do, you'll be surprised — as I continually am — at how bright and easy it is. If you have school-aged kids, bundle them up and take them with you. They'll be up anyway and may appreciate sharing a few minutes of sky with Mom or Dad. Send them off on the bus with their heads full of planets.

The post See Mercury First, Then Have Breakfast appeared first on Sky & Telescope.

Akatsuki Spies Massive Wave on Venus

Sky&Telescope -

Japan's Venus orbiter has witnessed a huge atmospheric wave that spans the globe.

Akatsuki at Venus

An artist's conception of JAXA's Akatsuki spacecraft at Venus.
JAXA / Akihiro Ikeshita

A monster wave roils in the atmosphere of Venus. The Akatsuki orbiter team, under the Japanese Aerospace Exploration Agency (JAXA), recently revealed images of the huge bow-shaped wave in the upper atmosphere of Venus.

The finding comes from data Akatsuki gathered in late December 2015 and early January 2016, shortly after orbital insertion. The team released the results on January 16th in Nature Geoscience.  The spacecraft's Longwave Infrared Camera (LIR) and the Ultraviolet Imager (UVI) captured the images of the Venusian atmosphere.

Venus gravity wave

Anatomy on a gravity wave on Venus. The orange images were captured by Atkatsuki's Longwave Infrared Camera (LIR), while the blue upper right image is from the spacecraft's Ultraviolet Imager (UVI). The solid line marks the planet's equator, while the dashed line denotes the day-night terminator.

Making Waves

The bow-shaped feature spans the Venusian cloudtops from hemisphere to hemisphere, more than 6,200 miles (10,000 km) long. Although the cloud tops whip along at 100 meters per second (200 mph) — much faster than the slow-moving surface of the planet below — the curious structure seems to stay in lockstep with the rotation of the planet, suggesting a complex (and previously unsuspected) interplay between the mountainous surface and the sulfurous cloudtops. The structure appeared near the evening terminator on the daytime side of Venus.

Akatsuki watches gravity wave

This data shows the gravity wave in motion, as observed by Akatsuki.

It's unclear at this point just how common such a wave is. When Akatsuki looked back at the region later in 2016, the wave had, for the most part, vanished.

A solar system oddball, Venus rotates retrograde (backward) once every 243 Earth days, longer than its 225 day orbital path around the Sun — its day is longer than its year. You could outrun sunrise and sunset on Venus if, of course, you could find a way to avoid getting simultaneously fried by the 864° Fahrenheit (462° Celsius) surface temperatures and crushed under an atmospheric pressure more than 90 times that of Earth's at sea level. The atmosphere consists almost entirely of carbon dioxide, with some nitrogen and sulfur dioxide.

The wave that Akatsuki detected is embedded in the cloud interface layer between the upper troposphere and the lower stratosphere. Computer models run by the the team, led by Makoto Taguchi (Rikkyo University, Tokyo), suggest that air flowing over the mountainous terrain produces a gravity wave that then propagates upward to the cloud tops, where the large bow wave is seen.

We see similar gravity wave phenomena here on the Earth, though not on such a large scale. NASA's New Horizons spacecraft also chronicled evidence for gravity waves in the atmosphere of Pluto during its historic 2015 flyby.

It's worth noting that gravity waves propagated through a planetary atmosphere are a distinct and separate phenomenon from gravitational waves, ripples in spacetime produced when black holes merge (among other events) detected by LIGO.

Gravity Waves on Earth

Gravity waves seen in the atmosphere of Earth.
GSFC / MODIS / Land Rapid Response Team / Jeff Schmaltz

The longitude of the bow-shaped wave corresponds with the western slope of the Aphrodite Terra highlands below, which NASA's Magellan spacecraft first mapped starting in 1990. The wave is warmer than the surrounding atmosphere and is brightest around 230 Kelvin (–40°C/F).

Meaning “Dawn” or “Daybreak” in Japanese, Akatsuki was launched atop an H IIA rocket from Tanegashima, Japan, along with the IKAROS solar-sail demonstration mission on May 20, 2010. Akatsuki took the long road, as the spacecraft missed getting into orbit in late 2010 and had to wait until early December 2015 to enter orbit around Venus.

Akatsuki Orbit

Observation phases for the Akatsuki mission along its elliptical orbit.

Akatsuki currently takes 9 days to orbit Venus, traveling from an apocytherion (farthest point) of 270,000 miles (440,000 km, just a little farther than the Earth-Moon distance) to a pericytherion (closest approach) of just 250 mi (440 km, the orbital altitude of the International Space Station) above the Venusian cloudtops.

Future Exploration of Venus

Akatsuki is currently the only robotic emissary in operation around Venus. The recent Discovery-class mission selections by NASA passed over two Venus mission proposals, in favor of the Lucy and Psyche missions. There is, however, a Venus proposal (the Venus In Situ Explorer, featuring an atmospheric probe and lander) in the running for the initial round of New Frontiers selections expected to be announced this coming November, with a final selection slated for 2019.

Now is also a great time to spy Venus at dusk, as the planet just passed greatest elongation on January 12th and is paired with Mars through the end of the month.

And speaking of amateur observations of Venus, skilled astro-imagers have managed to tease out actual detail on the Venusian cloudtops and even the surface of Venus using infrared and ultraviolet filters . . . though unfortunately, “Akatsuki's wave” is elusive at the wavelength favored by amateur imagers.

We're starting to appreciate just how complex the atmospheric interaction on Venus is, thanks in part to the intrepid Akatsuki spacecraft.

The post Akatsuki Spies Massive Wave on Venus appeared first on Sky & Telescope.


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