Glaciers once plucked the valleys of Mars … and will again

Posted on February 3, 2012 by astrobob

Sure sign a glacier came by - a big rock called an erratic along the shore of a lake in the Boundary Waters canoe area in northern Minnesota. Photo: Bob King

Glaciers. If you live in the northern half of the U.S. or Alaska it’s hard to go anywhere without seeing the effects of the two miles of ice that once drove slower than your grandmother over this landscape. Thousands of lakes left over from melting ice, rocks scraped and gouged by other rocks dragged by the ice and stray boulders called erratics that pop up in the middle of nowhere courtesy of the retreating ice. Digging a garden means tired arms not only from shoveling but from pitching rocks.

A current day mountain glacier looks like a river of ice with tons of laced with dark rocks scraped from the valley bottom and valley walls between the peaks. Credit: NASA

Last weekend I skied to an overlook on the Lester River near my home to check on the progress of two big glacier-sown boulders wedged in the dirt near the top of the river’s channel. Erosion exposed them them to view sometime in the past; this year gravity finally got the upper hand and yanked them down the slope and into the river. Was anyone there to hear this single tock of the geological clock?

The ice departed northern Minnesota some 10,000 years ago, but glaciers still populate the Arctic, Alaska and mountain ranges across the planet. One of the key features of glaciers are the junk they leave behind. The rocks and soil plucked from the landscapes they travel over and the debris that tumbles from the valley walls they squeeze through is carried forward by the moving ice. Later, as the climate warms and the ice melts back, the debris is dropped into large piles of rock called moraines.

The Marseilles terminal moraine southwest of Chicago is the low rise in the distance. It was once a bare ridge of rocky debris left by a departing glacier; now it's covered in trees.

If you’re driving across Minnesota, Wisconsin or Illinois and see a long, low ridge up ahead, there’s a fair chance it’s a moraine, or a pile of rocky debris along a lobe of a melting glacier.

An unnamed crater on in the Martian northern lowlands with with loop-shaped ridges interpreted as drop moraines left by retreating frozen carbon dioxide glaciers. The crater is about 22 miles across. Credit: NASA

Glaciers also appear to have been at work on Mars. Recently, members of the Planetary Geomorphology Working Group of the International Association of Geomorphologists described “drop moraines” in three regions of Mars created by extinct glaciers made not of water but of dry ice. These cold-based or polar glaciers are nearly frozen to the bedrock. Drop moraines form only in the coldest environments when a glacier advances and then stabilizes for a time in one spot. Rocks carried down by the glacier drop out as the ice vaporizes directly from solid to gas instead of melting first into liquid. Voila! – drop moraines.

At this location on Mars, overlapping of the moraines suggests 5 to 7 episodes of advance and retreat of the glaciers. Each time the glaciers dropped debris scraped up from the crust and deposited it as ice vaporized when the climate warmed just as on Earth. Credit: NASA

In the top picture, the loopy ridges of extinct lobes around the central peak of the crater suggest that the glacier that left them was about a thousand feet thick. Scientists hypothesize that the glaciers formed millions to tens of millions of years ago due a shift in the tilt of Mars polar axis. Mars’ axis swings through a large range – believed to vary from 11 to 49 degrees -  due to the gravitational tugging effects of the other planets over the long haul of time.

The tilt of Mars' axis varies over a 124,000-year cycle. A steeper tilt means a generally warmer climate; a slight tilt a colder one. Credit: NASA

Earth’s axial tilt in relation to its orbit (called obliquity) varies only about 3 degrees thanks to the stabilizing influence of the moon. No Mars. During a time of low tilt or obliquity, scientists speculate that carbon dioxide, the main ingredient in Mars atmosphere, condensed out as snow that accumulated in the polar regions and formed glaciers.

The glaciers retreated during periods of high obliquity, when the sun traveled higher in the sky, the climate warmed and frozen carbon dioxide vaporized. Right now Mars’ axis is tipped coincidentally at 25 degrees, nearly the same as Earth’s 23.5 degrees. It seems every time astronomers take a closer look at the Red Planet, they inevitably discover a facet of its personality relating to something on our own planet. I suspect gardening on Mars is likely to be just as tedious as it is in my backyard.

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Comet Garradd pays a visit to a Herculean star cluster

Posted on February 2, 2012 by astrobob

Comet Garradd photographed this morning (Feb. 2) near the globular cluster M92 in Hercules. The dust tail points to the left (east) of the comet's bright center called the coma. The gas tail points to the upper right. Credit: Michael Jaeger

Binocular and telescope owners can watch a fine match-up of the sky’s current brightest comet – Comet C/2009 P1 Garradd – and the rich cluster M92 in Hercules tomorrow morning. The cluster belongs to an ancient group of spherical, star-packed clusters called globulars. Some 330,000 stars are jammed into a ball 109 light years in diameter 26,000 light years away. Despite that rather spectacular distance, it still shines brightly enough at magnitude 6.4 to be easily visible in a typical pair of binoculars from moderately light polluted skies. Look for a small fuzzy spot with a brighter center.

Comet Garradd will be another fuzzy patch only a half a degree to the right or west of M92, so both little glows will be close together in the same field of view in any pair of binoculars. As you’d expect, the comet is much closer to Earth at 142.8 million miles. The separation between them will increase in the coming mornings as Garradd tracks slowly northward through Hercules.

Garradd's two tails point away from each from a combination of the comet's location high above the plane of the planets and our perspective of it from Earth. Blue arrows show the direction the comet's moving along its orbit. Credit: NASA/JPL with my own additions

In the diagram above, you can see that the comet has a steeply inclined orbit that takes it well above the plane of the solar system where the planets orbit. That’s why we see it high in the northern sky this month far from the morning planets. Comets that pass relatively close to the sun typically develop two tails – one made of dust carried away by the pressure of sunlight along the comet’s orbit and an ion tail of gases that fluoresce when they’re excited by the ultraviolet energy in sunlight. The dust is released into space as the heat of the sun vaporizes cometary ices.

This map shows Comet Garradd in the coming 10 days as it glides through the constellation Hercules. Stars are shown to 8th magnitude. Click the image for another map showing how to easily find Hercules. Created with Chris Marriott's SkyMap software

Since ion tails always point directly away from the sun, while dust tails lag behind in the curve of a comet’s orbit, the two tails point in different directions. Depending upon the sun-Earth-comet viewing geometry, they sometimes overlap or appear separated from one another by varying degrees. Our current viewing angle – looking up from way down below Garradd’s orbit – accentuates the tails’ separation.

The best time to see Comet Garradd and M92 is about 1 1/2 – 2 hours before sunrise, when it’s highest in the eastern sky before morning twilight begins. A small telescope will show the bright coma and a hint of both tails; telescopes of 8 inches or larger will show both tails stretching faintly more than a degree from comet’s head. Seeing a pile of stardust right next to bright, nearby comet should make for a beautiful sight. Try to get out in the next few mornings before moonlight becomes a problem.

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Seeing stars the American Indian way

Posted on February 1, 2012 by astrobob

Our familiar star patterns have ancient origins in Near East, Greek and Roman mythologies.

Many of the most familiar constellations were handed down from the ancient Babylonians, who lived in what is now Iraq, the Greeks and Romans. No doubt some of these star groups go back even further. Nowadays we speak of Orion, the zodiac constellations, the Dippers and bright stars like Sirius and Vega  thanks to storytelling and later through writing. More recently, all this wisdom has been converted into strings of ones and zeros and packaged for mobile phones and iPads.

Other civilizations and human tribes recognized their own sets of constellations. Some are similar to ours, others completely different. The Chinese had their Firebird and Crooked Running Water while the Australian aboriginal peoples recognized a great Emu among the starless patches dotting the length of the Milky Way.

Several weeks ago, my friend Eric, a fellow member of the Arrowhead Astronomical Society, presented a short program on star charts. One of the pictures showed a wonderful American Indian star chart with clearly recognizable constellation patterns.

The Skidi Pawnee star chart made using mineral pigments on tanned elk skin depicts star patterns important to the tribe's religion and culture. At the end of this article, I've included a labeled version of the chart.

After a bit of research I discovered it was made around the year 1700 by the Skidi Pawnee tribe in central Nebraska. The chart measures 22 x 15 inches and is part of the collection at the Field Museum of Natural History in Chicago. It was included in a collection of objects sacred to the Skidi they called the Big Black Meteoric Star bundle. The buckskin map may have been used to wrap a meteorite according to some sources.

The chart seems simple at first glance but includes many aspects of the sky. At either end are the warm orange tones of twilight that may indicate the east and west directions. The tiny stars running down the middle represent the band of the Milky Way which the Skidi saw as the Pathway of the Departed Spirits, the road walked by the souls of the dead. It divided the sky into two halves.

The Skidi Pawnee Council of the Chiefs appears to be a perfect match to our own Corona Borealis or Northern Crown

At the center of the chart to the left of the Milky Way is a large semi-circle of 11 stars called the Council of the Chiefs. It’s a dead ringer for our familiar Northern Crown or Corona Borealis. The chiefs watched over the people from the sky. The North Star, depicted directly above the semi-circle, watched over them both in turn.

From the North Star, you can follow the outline of the Little Dipper and below it, the Big Dipper. The North Star’s importance in Skidi religion is reflected in its bigger size despite being the same brightness as the stars of the Big Dipper.

They called it The Star That Does Not Walk Around, one of the best names for this special star I’ve ever come across and a reference to its stationary position in the sky at the end of Earth’s imaginary north polar axis. The bowls of the two Dippers were stretchers carrying gods who took sick during the ordering of the heavens and Earth at the beginning of time. Each is trailed by made a Medicine Man, his wife and an Errand Man – what we see as the Dippers’ handles.

The Hyades Star Cluster and Aldebaran form the face of a bull in our constellation Taurus.

Near the bottom of the Milky Way is a pair of stars thought to represent the two stars forming the “Stinger” in tail of Scorpius the Scorpion, a constellation pictured as a snake by the Skidi. It’s the gently bent line of stars below the double star

The opposite half of the sky features the six brightest stars in the Pleiades or Seven Sister Star Cluster and near it the V-shaped Hyades Cluster and bright star Aldebaran. Several other additional groups are shown on the labeled map below.

To help you out, here's a labeled version of the Pawnee star chart. Coma stands for Coma Berenices, a large faint star cluster/constellation in the spring sky. Bright stars Capella, Sirius, Vega and Antares had special status because they held up the roof of the sky. Antares is on the chart; perhaps the other three are too.

The sky and stars were extremely important to the Skidi. The doors of their lodges faced east to the morning sun and the round smoke hole in their dwellings ceilings was symbolic of the Council of the Chiefs star group. They believed their people were descended from the stars and the lodges in each village were arranged in a pattern that reflected particular star groupings above.

Pawnee lodges at Loup, Nebraska with a family standing at a lodge entrance in 1873. Credit: William Jackson

The star chart was a sacred object conferring knowledge of the sky and important traditions across the generations. Since the individual stars and groups were symbolically important, we shouldn’t be too concerned if the layout doesn’t exactly match what we see in the sky. For me, the connection this map makes between two very different cultures reminds us of our common humanity and fascination with the sky. And while science concerns itself with the positions and physical properties of stars, giving us many reasons to stand in wonder and awe under the firmament, myths and stories add another layer of understanding. Our ancestors looked to nature near and far not only for instruction but to imbue life with meaning and purpose. We still do today.

If you’d like to delve into Skidi Pawnee astronomy and myth in more depth, please check out my sources for this article:

* Stars and Constellations of a Pawnee Sky Map by Ralph Buckstaff
* Living the Sky: The Cosmos of the American Indian by Ray Williamson
* The Cosmology Bus blog entry on the topic

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Astronomy’s an adventure and don’t let anyone tell you differently

Posted on January 31, 2012 by astrobob

Photo taken January 16 from the International Space Station of the 62-mile diameter Manicouagan Crater in northern Canada, one of the oldest impact craters known. The feature was formed about 200 million years ago. An ring-shaped lake fills the crater's outer rim. Credit: NASA

Dawn space station passes for the U.S. will wind down this week, so if you’re a morning person, the next few days will present several nice opportunities to see the magnificent flying machine. Starting this Saturday the station will be making daytime passes only until it returns to the evening sky on or around Feb. 12.

* Tomorrow February 1 beginning at 6:27 a.m. Fine bright pass across the southern sky. At 6:28 the ISS zips under the planet Mars and a minute later under Saturn. Enjoy the ride!
* Wednesday Feb. 2 at 5:33 a.m. Brief, bright pass in the south-southeast
* Thursday Feb. 3 at 6:11 a.m. Low pass in the south

These are viewing times for the Duluth, Minn. region. For times for your town, please login to Heavens Above or enter your zip code at Spaceweather’s satellite flyby site.

A computer-created illustration of Rochechouart crater shortly after its formation some 200 million years ago. Credit: Frederic Michaud

The crater shown in the photo was created by as asteroid about 3 miles in diameter between 206 and 214 million years ago. Geophysicist David Rowley of the University of Chicago along with several colleagues has proposed that the Manicouagan Crater may have been just one of five multiple impact craters that formed at the same time from the breakup of a comet or asteroid. The others are the Red Wing Crater in North Dakota (5.6 miles diameter), Saint Martin in Manitoba (25 miles), Rochechouart in France (13 miles) and Obolon’ in Ukraine (12 miles). To learn more about the many craters identified to date on planet Earth, click over to the Earth Impact Database.

The inset photo shows Comet Shoemaker-Levy 9 in January 1994 when it was shattered to pieces by Jupiter's gravity. Six months later the fragments fell into the planet creating a series of black, sooty scars in its upper cloud deck. Credit: NASA/Hubble Space Telescope

The idea is plausible based upon similar ages and alignment, taking into account tectonic plate movements in the intervening 200 million years. We’ve also seen something like this happen before but not on Earth. Between July 16 and July 22, 1994 Comet Shoemaker-Levy 9, which was captured by the planet Jupiter, broke up into multiple pieces which rained down in succession into the planet’s cloud tops. Flashes from the explosive collisions with the atmosphere were recorded by the Galileo spacecraft at the time. Back on Earth, amateur astronomers thrilled to the parade of dark impact blotches that ringed Jupiter like an onyx necklace.

The lines on the map show the path of the July 10, 1972 total solar eclipse. Credit: NASA

I have a personal story to share about the Manicouagan Crater area. On July 10, 1972 the centerline of a total eclipse of the sun passed just south of the crater. My buddies Rick and Larry and I were working in northern Wisconsin at the time and decided to drive up and see the eclipse. We bought a few groceries and piled into Larry’s green Vega for a very long drive across Michigan and up through Canada into Quebec. As I recall, we made a left turn inland at Baie Comeau on the St. Lawrence River and drove until we hit the inevitable dirt road somewhere in the middle of the forest near the centerline. There we set up camp along a river the evening before the eclipse.

I don’t remember when we noticed the black flies, but they became an increasing problem the next day. We wandered along the river looking for a scenic spot to watch the rare event that afternoon. Just before totality, clouds obscured the sun, leaving us with little more than a few minutes of pseudo-darkness. No spectacular corona, no flaming pink prominences, no once-in-a-lifetime spinal chill.

While this was obviously a disappointment, more disturbing were the flies. We were fresh Wisconsin sausage in their tiny eyes and they pursued us now relentlessly. I had so many bites on the back of my neck and ears my fingers were bloody from scratching.

We hurried back to take down the tent, literally ran for the car and got the hell outta there. My fondest memory of the event was relaxing in a bathtub later that night in a motel in Baie Comeau nursing my bitten body. Astronomy’s full of adventure and don’t let anyone tell you differently.

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Ina Caldera – one of the moon’s coolest, hottest mysteries

Posted on January 30, 2012 by astrobob

Ina Caldera sits atop a low, broad volcanic dome or shield volcano, where lavas once oozed from the moon's crust. The darker patches in the photo are blobs of older lunar crust. They're "domed" or higher than the rougher surface below. Credit: NASA

In the March 2012 issue of Sky and Telescope magazine there’s a fascinating short article about a possible lunar volcanic landform called Ina Caldera. This 2-mile long D-shaped patch looks like nothing I’ve ever seen on the moon.

Blobs of older, crater-pitted lunar crust rise some 250 feet above the younger, rubbly surface like melted cheese on pizza. Brighter areas on the moon generally indicate younger surface features. Solar and cosmic radiation darkens airless worlds like the moon and asteroids over the long haul of time. The rough area between the “islands” of older crust doesn’t have as many craters either – another sign of its relative youth.

Ina was first noticed only as recently as 1971 when photographed by the astronauts aboard Apollo 15. Recent photos taken by the low-flying Lunar Reconnaissance Orbiter (LRO) show a level of detail that reveal how unique this curious feature really is. So what’s going on in Ina?

Steam issues from the active volcano Nyiragongo in the Democratic Republic of the Congo in May 2010 as photographed by satellite. Credit: NASA

Theories abound. In a real volcano, calderas are caused by the collapse of material at the volcano’s top after magma from below has drained away following an eruption. Perhaps the top of the low volcanic dome on which Ina sits collapsed unevenly and relatively recently to form the patchwork we see today. Another possibility is that magma from below heated trapped gases like carbon dioxide and water to such high pressures they violently blasted right through the crust, sending rock and debris flying for miles in the moon’s low gravity field.

This photo shows the moon at 8 days old, but the lighting should be good on tonight's 7-day-old moon to look for Ina. Ina is located just south of the arc of the Apennine Mountains in the moon's northern hemisphere almost midway between the craters Conon and Manilius. Photo: Bob King

Other researchers with the LRO mission agree that Ina’s two terrains are a contrast of young and old but don’t think the old bumpy areas are as ancient as assumed. Additional high resolution photos from the orbiter show a good number of craters there, many with soft rims.  I encourage you to explore Ina yourself by going to the LRO’s ACT-REACT Quick Map and entering its latitude of 18.65 and longitude of 5.31. As you zoom in, you’ll feel like you’re coming in for a landing.

Extreme closeup of a small portion of Ina's interior. It takes a little effort, but the smoother areas are rounded blobby "islands" atop the rough terrain. Credit: NASA

Whatever happened created an enigmatic moonscape that scientists are still trying to understand. In so many ways, the moon is an undiscovered world. With just six short visits during the Apollo era and 150 lunar meteorites collected on Earth, we’ve barely scraped the lunar regolith.

You can appreciate how small the Ina Caldera is this spectacular closeup photo taken by Alan Friedman. Find the Apennines and Conon crater on the range's southern flank, then navigate toward Manilius using high magnification. Click to see the complete high resolution image. Copyright Alan Friedman/avertedimagination.com

One of the constant joys of amateur astronomy is seeing with your own eyes what you read or heard about. And trust me, you can see much more than you might think. Even Ina. While most of you will explore via the ACT-REACT map, if you’ve got an 8-inch or larger telescope and you’re generally familiar with the moon, you can start hunting for Ina this evening. This tiny feature is most easily visible when light strikes it from a low angle as it will on tonight’s first quarter moon. If it’s cloudy tonight, try again over the next few nights. Hope for calm air, use high power and you might just be able to spot this enigma.

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Moon, Jupiter, Mars strut their stuff tonight

Posted on January 29, 2012 by astrobob

The half moon glides by brilliant Jupiter the next two nights. Map created with Stellarium

Cast a glance upward at the moon tonight. That big, bright object just a few degrees to its south is the planet Jupiter. The two will be sky buddies the next couple evenings.

Through binoculars the 6-day-old moon will reveal a variety of crisp-edged craters along the terminator, the boundary between lunar day and night.  Most prominent tonight is a remarkable chain of impact craters – Theophilus, Cyrillus and Catharina.

Theophilus is named after an ancient Greek geographer and measures 68 miles across. It fairly fresh as lunar craters go, with a sharp-edged rim and a couple of distinctive central mountain peaks. Theophilus overlaps the much older Cyrillus, which is 61 miles across and named for a 4th century theologian.

One of the best known features on the moon is the Theophilus crater chain. Watch for it tonight in a small telescope. Photo: Bob King

Scientists determine relative crater age by looking at which craters overlap others (the ones on top are younger) and noting how worn or broken their rims are. Cyrillus’s rim is worn down and much less crisp than Theophilus to the north. The final crater is the chain, Catherina, named for St. Catherine, a Greek theologian and philosopher, is 62 miles across and even more beaten down than Cyrillus.

Jupiter, its moon Io and Io's shadow tonight at 6:30 p.m. CST. South is up as viewed in most telescope. Credit: Meridian

You should be able to spot the trio in binoculars, but the best view will be through a telescope. And it doesn’t have to be a big one. Even a cheap department store scope will do the job. While you’re at it, point it at Jupiter. The two most prominent stripes – the North and South Equatorial Belts – are easy to see across the planet’s midsection. This evening the shadow of Jupiter’s moon Io will hover over the South Equatorial Belt from 5 to 7 p.m. CST. Look for a tiny, inky-black dot. Io itself will shine brightly nearby due west of the planet.

Finally, Mars rises around 8:45 p.m. and is high enough by 11 p.m. to have cleared the atmospheric muck for a sharp view. With a 4-inch or larger telescope magnifying around 150x, not only is the north polar cap a snowy white oval, but the planet’s most obvious dark marking, Syrtis Major, is front and center. This vaguely triangular patch is an enormous extinct shield volcano. Another easy feature to look for is the fat, dark rim along the polar cap called Utopia. The second of the two Viking landers touched down there in September 1976.

Even small telescopes can pick out some of Mars' more obvious features this week. Credit: Damian Peach

Because a day on Mars is 37 minutes longer than Earth’s, all Martian surface features gradually drift to the east as the nights go by. Tonight Syrtis Major and Utopia face us square on around 11:30 CST, tomorrow they’ll do so around midnight and on the 31st around 12:30 a.m. They’re also easily seen up to a couple hours before and after those times.

In the coming weeks, I’ll have more tips on how to observe the Red Planet as we approach opposition in March.

If it’s clear the next few nights, don’t miss this opportunity to spot several of Mars best landmarks.

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The biggest star in the sky and how to see it

Posted on January 28, 2012 by astrobob

Canis Major hosts the brightest star in the sky, Sirius, as well as our featured star VY. You'll find Sirius twinkling brightly about halfway up in the southern sky around 10 o'clock.

Astronomy is full of superlatives. Farthest, closest, hottest, densest, biggest, smallest. It’s fun to prowl around the sky in search of these extremes.

Two nights ago, I found myself star-hopping across Canis Major the Greater Dog in search of this or that gas cloud and spotted the star VY Canis Majoris on my atlas. The use of the lettered name “VY” tells us first off that this is a variable star whose light is not constant like the sun’s.

A quick check on the American Association of Variable Star Observers (AAVSO) website shows that VY varies between magnitudes 7.4 at brightest to 9.6. For the past few months it’s been around 8.0, bright enough to see in ordinary binoculars.

But its variability is not exactly the reason I wanted to acquaint you with this star. VY  is special for an entirely different reason – it’s the largest star known! Astronomers estimate its diameter at some 2,000 times the size of the sun. And since the sun is no slouch at 864,000 miles across, VY is truly a monster.

Illustration showing the size of the sun compared to VY Canis Majoris

Put in place of the sun at the center of the solar system, it would puff out beyond the orbit of Saturn. If the sun were reduced to the size of one of those big rubber balls people use as chairs these days, VY would be a much bigger ball 1.4 miles across. Yet another way to think of its vast girth is to compare how long it would take jet airliner traveling at 550 mph to fly across Earth, sun and VY:

* 14.5 hours non-stop to fly across Earth’s diameter of 8,000 miles
* 65.5 days to cross the sun
* 394 years to complete the 1.9 billion mile flight across VY

Thinking about that makes me want to stand up right now and stretch my legs.

VY is about 5,000 light years from Earth and classified as a red hypergiant star with a temperature of some 5000 degrees F. Surrounding the star is a small nebula of dust and gases VY has expelled in fits and starts during its evolution from a white supergiant star to its present state. Really big stars like VY eventually run of off nuclear fuel in their cores, collapse under the pull of gravity and then explode as supernovas. VY is so enormous that scientists predict it will one day become a powerful hypernova – ah, yet another superlative! – and might even collapse to form a black hole.

Use this detailed map, which shows stars to about 8th magnitude, to star-hop to VY and two other sky delights. North is up. Click map to go to the AAVSO site where you can print a more detailed map suitable for estimating VY's changing brightness. Maps created with Stellarium

You have plenty of time to see this magnificent star before that happens. First, shoot a line through the belt of Orion towards the east until you come to Sirius. An outstretched fist below Sirius, find a triangle of three easy-to-see stars, then use the detailed map (above) to star-hop your way to VY just as I did. For reference, the “triangle” fits nicely in a the field of view of typical binoculars.

NGC 2362 is one of the finest overlooked clusters in the sky. Credit: NASA

Those with telescopes are in for a treat. If the air is steady and you study VY closely at medium and higher magnifications, you’ll see a very small red-colored nebula around the star.This is material that’s been expelled during the star’s outbursts.

I’ve also included two other “must-sees” on the map — the beautiful, colorful double star h3945 which any scope can split into two and the stunning little cluster surrounding Tau called NGC 2362. See them all and you’ll have a most satisfying night.

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Zippy little asteroid 2012 BX34 makes a quick visit

Posted on January 27, 2012 by astrobob

Funny how linear things are in Orion's Belt and Sword. This 21-minute long time exposure with a 120mm lens shows the trails of the three Belt stars at top and the Sword. The slightly fuzzy trail of the Orion Nebula is the middle stripe near bottom. Photo: Bob King

I had a good night under the stars last night. Temperatures in the 20s made it easy to be outside for a change. It also meant I could make a few time exposures without having to worry about running out of battery power. Winter’s Milky Way is fainter and less textured than the summer version with its chunky star clouds. From a rural site, it slices diagonally from right to left across the southern sky and reminds me of rising smoke from a smouldering campfire. Knowing that it’s jammed with billions of stars thousands of light years thick jazzes my brain every time I see it.

The Milky Way last night around 10 o'clock. Sirius is at bottom; Orion with his 3-starred Belt and Sword dangling below is at right. Details: 15mm lens at f/2.8, ISO 3200 and 30 second exposure. Photo: Bob King

A 36-foot wide asteroid skimmed near Earth at 9:30 a.m. CST this morning passing only 36,750 miles away before zooming back into the deeps at more than 21,000 mph. No danger was ever expected from 2012 BX34, since a rock that size would disintegrate into pieces if it were to strike our atmosphere. At best we might expect a few meteorites. No worries. The asteroid’s path was well known beforehand and any chance of a collision ruled out.

Some amateur astronomers saw and photographed the object, but it was challenge, because 2012 BX34′s tiny size meant it was faint – only about 15th magnitude at best.

Asteroid 2012 BX34 is the faint streak to the right of the top star in this 2-minute time exposure photo taken early this morning. Credit: Ernesto Guido, Giovanni Sostero & Nick Howes

Several asteroids a year come closer to the Earth than the moon’s distance of 240,000 miles. 90% of the larger ones, ranging from mountain-size on up, are already known thanks to detailed surveys with both ground-based and orbiting telescopes. The tally stands at around 910 for the moment. 2012 BX34 ranks 15th on the list of closest approaching asteroids. Below are the top ten as of January 27, 2012 along with their distances at the time of closest approach to Earth:

1. 2011 CQ1 – 3,405 miles on Feb. 4, 2011
2. 2008 TS26 – 3,821 miles Oct. 9, 2008
3. 2004 FU162 – 4,060 miles March 31, 2004
4. 2011 MD – 7,500 miles June 27, 2011
5. 2009 VA – 8,699 miles Nov. 6, 2009
6. 2008 US – 15,534 miles Oct. 20, 2008
7. 2004 YD5 – 20,000 miles Dec. 19, 2004
8. 2010 WA – 24,000 miles Nov. 17, 2010
9. 2011 CF22 – 24,000 miles on Feb. 6, 2011
10. 2008 VM – 29,760 miles on Nov. 3, 2008

The list is interesting because the closest approaches have all been within the past few years. Are we suddenly being buzzed by more asteroids? No. What you’re seeing is a selection effect due to improvements in equipment, cameras and deliberate surveys to hunt for Earth-approaching asteroids that might pose a threat to Earth now or in the distant future. It’s a little like hunting for blueberries in the forest. After you find the first patch and get familiar with the look of the leaves and habit of the plant, you suddenly start seeing blueberries everywhere.

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Comet Lovejoy pokes its head above Arizona’s horizon

Posted on January 26, 2012 by astrobob

Multiple time exposure pictures were "stacked" together to make this deep image of Comet Lovejoy. Some of the "black snow" is camera noise, much of it is very faint stars. The bright star Sirius is at upper right. Click image to see Rob's nice website devoted to the comet. Credit: Rob Kaufman

A question from a reader this morning stirred me to post this update on Comet Lovejoy, the great sungrazing comet of 2011. While the brightest part of the tail near the nearly-vanished head of the comet is now visible from the southern U.S., it’s exceedingly faint. I know of only one observer at this time who has succeeded in seeing it – Alan Hale, co-discoverer of one of the best known comets of our time, Comet Hale-Bopp. Twice this past week he used a 16-inch telescope to eke out the extremely faint glow of the comet’s head / tail. His first observation was made Sunday night:

“I had excellent sky conditions right down to the horizon. There definitely seemed to be an extremely pale and vague glow — not much more than a brightening of the background sky, but it seemed to be real.  It almost precisely followed the expected rate and direction of motion during the 1 1/2 hours that I followed it,” wrote Hale in an e-mail today.

He spotted the same faint glow last night (25th) moving in the same direction. Both times Hale estimated its brightness at 12.0, but because the comet’s light was so spread out, it was much more difficult to see than a typical smaller 12th magnitude comet.

Comet Lovejoy in its glory days photographed from Australia on Dec. 26, 2011. Credit: Rob Kaufman

From the southern hemisphere, where Comet Lovejoy is much higher in the sky, amateur astronomer and comet discoverer David Seargent spotted it with large 25 x 100  and 15 x 80 binoculars on Sunday the 22nd. His description matches Hale’s – a very faint glow. Meanwhile, astrophotographer Rob Kaufman of Australia pushed his camera equipment to the limit to record an impossibly faint 26-degree long tail. His picture (above) is a negative image to better show the contrast between comet and sky. What’s cool about the photo is that the tail pokes north almost to Sirius in the constellation Canis Major, stars widely visible from anywhere in the U.S. and southern Canada.

Pity that the better part of the tail is simply too dim to be seen with naked eye, binoculars or telescope. Unless you live in the far southern U.S. and have a moderate to large telescope, your chances of seeing Lovejoy are rapidly diminishing if only because the moon’s phase is waxing.

Comet Lovejoy on Dec. 22, 2011 reflected in water. Credit: Colin Legg

Bright moons kill faint comets. By the time Comet Lovejoy is high enough to be better placed for viewing in the mid-northern states next week, the moon will be on its way to full, making it impossible for anyone to spot it.

When the moon finally departs the early evening sky around Feb. 9, many amateur astronomers will be out for one last try at a visual observation. I’ll be among them. Even though Lovejoy will continue moving farther from Earth and fading in the coming weeks, I remain hopeful.

If you live in Arizona, Florida and other southern regions of the U.S. and Central America, now’s the time to seize the opportunity.

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Beautiful aurora! What makes it happen?

Posted on January 25, 2012 by astrobob

An amazing aurora display in northern Sweden last night. Details: Nikon D7000 camera, Tokina 11-16 2.8, ISO 1600, 5 second exposure. Click the photo to see his fantastic video of the entire night. Credit: Chad Blakely

Clouds! They were with us last night, but according to Mike Thiele, who observed from northwestern Minnesota, the storm had spent itself by the time it was night along the U.S.-Canada border: “Very weak display partially obscured by clouds about 4 a.m.,” he writes.

Earlier, during afternoon hours North American time, auroras raged across northern Europe. Sky watchers there called it one the best in years. Chad Blakely, who participated in the Lights over Lapland photo expedition in Abisko National Park in Sweden called it one of the most spectacular displays of aurora he had ever seen. “Words can not describe the excitement we shared and the sights we saw,” said Blakely.

Magnetic fields on the sun channel solar plasma - a hot gas composed of electrons and protons - into picturesque loops. Credit: NASA

Chad, I believe your photo negates the need to fumble with words. It’s a beautiful image that makes all wish we were there.

The storm and its wonderful auroras were on the fade by evening over the U.S. Though the intensity picked up a bit in the wee hours this morning, it never approached the levels seen in northern Europe and Siberia.

According to C. Alan Young, a NASA solar physicist, not all of the material speeding from the sun arrived at Earth. Rather we were struck by a more glancing blow. Had it been a direct hit in the right orientation for greatest storm effect, auroras would probably have been widespread across the U.S. as well.

As of 1 p.m. CST Earth’s magnetic bubble or magnetosphere is still reverberating from the shock with elevated levels of magnetic activity but nothing approaching a storm. The NOAA Space Weather forecast still calls for possible major storms with accompanying auroras today through tonight. If your weather is clear, I encourage you to look to the northern sky again tonight.

The normal solar wind of electrons and protons as well as faster-moving blasts caused by explosive solar flares sends material earthward, where it encounters our magnetosphere. Much of the plasma is deflected, but some creeps in through the tail-end or magnetotail. Credit: NASA

Billions of charged particles from the sun in the form of a coronal mass ejection (CME) are the first step in the making of a geomagnetic storm. Powerful explosions on the sun’s surface called solar flares launch this extremely tenuous cloud of material out toward the hapless planets at something like a million miles per hour. Yesterday’s CME was much faster – 4.5 million mph. The faster the particles travel, the sooner they arrive and the more energy they carry. Exactly like a speeding car. A crash at 10 mph is far less destructive than one at 65 mph. That’s why scientists predicted such a powerful storm yesterday.

When the cloud arrives in Earth’s vicinity it first bumps up against and then flows around the planet’s magnetosphere, a teardrop-shaped bubble of invisible magnetic energy much like the field around a typical refrigerator magnet. The magnetosphere is squished by the solar wind on the day side facing the sun and stretched out into a long ‘magnetotail’ on the night side of Earth.

Earth’s magnetic field is generated by the spinning of our iron-nickel core as the planet rotates on its axis. Hands down it’s the best defense we have against what the sun might throw at us. If Earth lacked a magnetosphere, high speed plasma clouds and the sun’s daily “solar wind” would sooner or later strip away our atmosphere with nasty consequences for all.

Illustration of electrons trapped inside the tail of Earth's magnetic field accelerating toward Earth's upper atmosphere to discharge in "sparks" of aurora. Credit: NASA

ANYWAY … the billions of charged particles – and we’re talking mostly electrons (negative charge) but also protons (positive charge) -  slide around the magnetic bubble, compressing and increasing its energy. Think of the air getting warmer as you pump a bicycle tire full – the air heats up from compression.

Meanwhile, some of the particles streaming past the bubble manage to link into the lines of magnetic force down at the tail end. The combination of compression and charged particle build-up on the opposite end of the magnetosphere generate powerful electric currents that push electrons toward the Earth’s magnetic poles at extremely high speeds. Something very similar happens in an old TV picture tube, where electrons are accelerated by thousands of volts toward a phosphor-coated screen. When they hit, the screen glows.

As they race earthward down magnetic field lines, the particles strike the upper atmosphere and crash into nitrogen and oxygen molecules some 50 miles or more overhead. The molecules are briefly excited to higher energy levels like someone buzzing with excitement during the reading of the daily lottery numbers. Moments later all those billions of oxygens and nitrogens return to their original “rest” states by losing energy in the form of green and red photons of light.  These are the colors of the aurora.

And what do we experience? Arcs, rays, spears of fast-moving color as solar plasma flies down those field lines and discharges all that pent-up electricity in bursts of molecular color. What a wonder that something so “mechanical” in nature could inspire so much awe. Such is the beauty of reality.

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