Monthly Archives: August 2011

Earth and moon seen from far, far away

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A "faraway" photo of the Earth (left) and the moon taken on August 26 from a distance of 6 million miles by the JunoCam, Juno's onboard camera. Credit: NASA/JPL-Caltech

Ain’t much to look at, is it? Yet it contains everything precious in our lives. This photo of the Earth and moon was taken by the Jupiter-bound Juno space probe from a distance of about 6 million miles last Friday August 26. That’s 25 times the distance to the moon from Earth. As the craft headed outward on its long journey to Jupiter, the mission team tested out its instruments -  including the JunoCam – to make sure everthing was in working order.

The Earth and moon photographed by the European Space Agency's Mars Express probe on July 3, 2005 at a distance of about 5 million miles. Credit: ESA

At first glance, the picture seems to show little more than two dots – amazing in itself if you let it sink in – but there’s more to see.  The Earth shows a blue fringe, hinting at water, while the moon is gray-brown. It’s also apparent that the Earth is considerably larger than the moon — 3.7 times to be exact.

Still frames from the Japanese Kaguya spacecraft orbiting the moon show a colorful Earth rising over the forbidding lunar landscape. Credit: JAXA

The difference in brightness between the two worlds is striking. The Earth is so much brighter than the moon because of light reflected from snow, clouds and the oceans. As seen from the moon, the Full Earth would appear 100x brighter than than our full moon. In comparison, the moon’s rocky, dusty surface reflects the same amount of light as a fresh asphalt road. Imagine sitting at a window inside a lunar dwelling reading a book by the light of Earth. A delicious thought that makes me a tad jealous of the future.

Watch for the moon to return to the western evening sky tonight. This map shows the sky about 15 minutes after sunset. Created with Stellarium

If you’d like to connect with your local moon, you can do so tonight by facing the west around the time of sunset. The 3-day old crescent moon will appear about four fists held at arm’s length to the left of the sunset point and very low.

Because the moon’s evening path slants well to the south in late August and September, it’ll take a couple more days before the moon’s increasing elongation from the sun angles it high enough for more convenient viewing. I don’t mind a low moon though. It gives us the opportunity to see a distinctive celestial body mingle with things terrestrial, poking out from behind homes and trees like a kid playing hide-and-seek.

Cepheus the King stands in the shadow of his Queen

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Cepheus the King (left) and Cassiopeia the Queen as depicted in an 1825 star atlas. In Greek mythology, they represented the king and queen of Ethiopeia

Anybody can find the W of Cassiopeia the Queen. Even if you’ve never seen the constellation, all I have to do is point and say “See that zigzag of five stars?” and it’s instant recognition. Not so with Cassiopeia’s husband and long-time companion, Cepheus. Five stars arrayed in a pentagon outline the form of Cepheus (SEE-fee-us) the King, who occupies the royal throne at the Queen’s side in the northern sky. It wouldn’t be the first time a king is overshadowed by his queen.

Because Cepheus isn’t far from the ever-present, never-setting North Star, it’s visible nearly year round for northern hemisphere observers. Here in Duluth, the he never sets, making him a member of the select group of what astronomers call the circumpolar constellations. Cepheus is overlooked by many, because his stars are fainter than Cassiopeia’s. Once you learn proper way to approach the king, I trust you’ll pay him a visit the next clear night.

Cepheus is wedged between the North Star and the zigzag W of Cassiopeia in the northern sky in early September. The hazy band is the Milky Way. Stars of interest are marked. Created with Stellarium

September is a perfect month to get to know the constellation as it’s high in the northern sky. Start with the W of Cassiopeia, now about halfway up in the northeast at nightfall, and focus on the star Gamma in the center of the W. Reach your fist to the sky and mark off three fists to the upper left to find Polaris, the North Star. Three more fists to the upper right will bring you to Cepheus’ brightest star Alderamin. Notice that Gamma Cas, Polaris and Alderamin form a nearly perfect equilateral triangle.

Now work your way via eyeball from Alderamin back toward Polaris to Arrai, a moderately bright star that forms the point of the pentagon. From there, follow back up the other side of the figure to Delta Cephei. Got it? That’s all there is to it.

Like any king, Cepheus keeps a trove of treasures and freely shares them with any sky watcher who makes the effort. Below you’ll find gems of interest for the naked eye, binoculars and telescope:

Arrai (or El Rai) — Notice that this star is just a short hop from the North Star. Because Earth’s axis slowly wobbles, it traces out a circle in the northern sky over a 26,000 year period. At the moment, the north polar axis points to Polaris, but about the year 4000 A.D., it will be pointing to Arrai in Cepheus. Quietly waiting in the background for now, Arrai will be crowned Pole Star on that future day. The star also is home to an extrasolar planet. Called Gamma Cephei Ab, the Jupiter-like world has about 1 1/2 times Jupiter’s mass and orbits the star in 2 1/2 years.

Xi Cephei — Pronounced ‘Zye SEF-ee-eye’, this is one of the most beautiful double stars and a personal favorite. Any telescope magnifying around 60x will split what appears to be a single star to the naked eye into a tight pair of stars, one white and the other orangish. The stars are magnitudes 4 1/2 and 6 and separated by 8 arc seconds. Xi is also known as Kurhah and located about 100 light years from Earth. Xi is also a great jumping off point to explore the “top” of the constellation in binoculars. The Milky Way passes through this area offering up rich star fields to delight the eye.

The Garnet Star — Also known as Mu Cephei, this star is a red supergiant (similar to Betelgeuse in Orion) and one of the largest stars in the entire sky. Sure doesn’t look impressive at 4th magnitude, but that’s because it’s over 1,800 light years away. If we could haul Mu to our solar system and put it in place of the sun, its surface would reach all the way to Saturn’s orbit. Mu’s other name – the Garnet Star – refers to its lovely, fiery red-orange color. Last night I looked at this monster in 10×40 binoculars and the color was obvious. A telescope shows it well, too.

Delta Cephei — Remember the throbbing, pulsating variable star Eta Aquilae we examined over the weekend? You don’t? Well, here’s the link. Delta is another star of the same ilk, and not just any one, but the prototype for the whole class. That’s why they’re called Cepheids after Delta Cephei. As Delta expands and contracts, it brightens and dims from magnitude 3.5 to 4.4 over a period of 5.4 days. That’s a big enough range to easily follow the changes with your naked eye. By good fortune, two neighboring stars of magnitude 3.4 (Zeta) and 4.2 (Epsilon) make ideal references. Last night Delta was sitting pretty at 3.9.

Comparison of the sun and the supergiant Mu Cephei (left). The time exposure photo of Cepheus at right shows some of the gems described in the blog. Credit: Windows2theUniverse (left); Bob King (right)

Delta is also an easy, bright double star like Xi but with a wider separation requiring only about 20x to split. Any telescope is up to the job. Look for the 7.5 magnitude companion star just 41 arc seconds away. As you bid the king adieu at night’s end, please offer a word of thanks for sharing his treasures.

Pinwheel Galaxy supernova headed for the record books

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Supernova 2011fe is framed by tick marks in the fine color photo of the Pinwheel Galaxy taken on August 28. Credit: Joseph Brimacombe

Well, it finally happened. Supernova 2011fe in the Pinwheel Galaxy broke the 12th magnitude barrier overnight and now joins a select group of about 14 other supernovae that peaked at that brightness or better. And the fun’s not over yet.

Last night I saw it easily at magnitude 11.7 in a larger telescope, but it was even faintly visible in my wee 4.5 inch reflecting telescope, one of the most common small scopes you can buy.

While the star will undoubtedly be brighter yet tonight, perhaps even cracking the Top Ten,  it probably won’t soar to the heights of the supernova that appeared in the Andromeda Galaxy in 1885*. That one shot all the way up to 5.8 and became briefly visible with the naked eye under dark skies. It was the first supernova seen in a galaxy beyond our own Milky Way. The more recent supernova 1987A in the Large Magellanic Cloud, a nearby satellite galaxy of the Milky Way, topped out even brighter at magnitude 2.8 in 1987 and was plainly visible without optical aid. And finally, we have to go back to 2004 and the galaxy NGC 2403 for the last supernova outside the Milky Way system that was as brighter than 2011fe is at present. Certainly that makes this event very special.

While there are physical differences in the supernovae that make one shine brighter or fainter than the other, the main reason why some are bright and some are not has more to do with distance. Other factors being equal, the closer to our own Milky Way a galaxy is, the brighter a supernova will appear. It’s the same with light bulbs — a bulb only two feet from your face looks a lot brighter than one a quarter mile away.

I encourage you to go out for a look if you have a telescope. As you’ve read, it’s not often we have such a stellar show. Here are links to two maps to help you find it. As of last night, SN 2011fe was the brightest star seen in the main body of the galaxy, outshining all the Milky Way foreground stars. When you look at the galaxy in your telescope and all you see is blurry spot and a single star shining within, that’s it!

Almost menacing in appearance, this new photo of Hyperion, taken from a distance of 15,000 miles, looks over a backlit cratered landscape. The moon rotates chaotically and may be a fragment of a larger moon liberated during a collision. Click to enlarge. Credit: Cassini team/NASA

Closer to Mother Earth, NASA recently released new photos from the Cassini Mission at Saturn of the odd little moon Hyperion. They were snapped during the August 25 flyby. The 168-mile wide Hyperion is composed mostly of ice and riddled with so many craters, it has the appearance of a giant sponge. Indeed, the moon’s density is so low, its interior may well be wormy with caverns.

Hyperion is peculiar in another way. It’s the only moon in the solar system known to rotate chaotically. Its axis of rotation wobbles this way and that so much, it was hard to know in advance exactly what part of the moon the Cassini craft would be photographing. Scientists believe its irregular shape, very elliptical (cigar-shaped) orbit and interactions with Saturn’s largest moon, Titan, may be behind its chaotic ways. Click HERE for more photos of Hyperion.

* References: Supernovae and how to observe them by Martin Mobberly, 2007
and David Bishop’s Latest Supernovae site

Comet Elenin tired of doomsday finger pointing

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Comet Elenin shows a fading, extended nuclear region instead of a dense, bright one in this photo taken Aug. 27 through an 11-inch telescope. Credit: Michael Mattiazzo

Maybe it just couldn’t take all the publicity. It appears Comet Elenin might be breaking up and fading. Recent observations from Australian comet observers indicate the comet, which began dimming a week ago, is still fainter than expected. A likely explanation is that the comet nucleus might be in the process of breakup. I mean how much hype can a comet handle?

A week after witnessing the comet’s dramatic fading on August 20, amateur astronomer Michael Mattiazzo of Castlemaine in Victoria, Australia noted that by last night (Aug. 27) the comet’s nucleus (bright inner region of the coma) had spread into “a dim, elongated diffuse smudge.”  He estimates Elenin’s brightness at 9th magnitude. For current pictures, click on over to Michael’s Southern Comets Homepage.

A closeup photo of the breakup of Comet S4 LINEAR taken on August 6, 2000 by the European Very Large Telescope (VLT) in Chile. The disintegration is a great demonstration of just how fragile comets are. Click photo to enlarge. Credit: ESO

Back in July 2000, the nucleus of comet C/1999 S4 LINEAR broke up into a shower of mini-comets and then faded away. I remember watching the comet brighten up nicely earlier that month, but just when predicted to reach naked eye visibility, it began to disintegrate. Through the telescope, the nuclear region – the bright spot in the center of a comet’s coma – became elongated and rapidly grew dimmer. Several nights later, S4 LINEAR was a ghost of its former self.

While I’d hoped to see a bright comet that month,  the changes were so sudden and the realization of what was happening so captivating, I didn’t mind the loss. On the contrary. Like seeing an animal in the wild, I was witness to a rare moment of insight into the lives of comets.

The elongation of the Comet Elenin’s nuclear is a good sign of a disruption, but it takes some days to spread out and cause the comet to fade further. There may even be fresh material exposed that could possible cause the comet to brighten temporarily, but the long-term prospects, if it indeed a breakup, will lead to the Elenin becoming much dimmer. It may not survive perihelion either, but I don’t want to get ahead of myself. One would hope a large telescope could be trained on Comet Elenin soon to confirm any breakup and provide more detailed photos.

Comet Garradd brushes the star cluster M71 in this beautiful portrait made this past Friday night. Credit: Rolando Ligustri

Before we leave the subject, I have to share this stunning image made by astrophotographer Rolando Ligustri in Italy of Comet Garradd. He captured the comet Friday night when its tail crossed in front of the rich globular star cluster M71 in Sagitta the Arrow. It was clear at my house too, and I was totally blown away by the scene through my telescope. You don’t see many conjunctions of bright deep sky objects and comets. This close pairing allows us to better picture a comet in three dimensions as a dusty wraith hovering in the foreground against a background of distant suns. The event took place in a part of the sky jam-packed with stars further adding to the beauty of the scene.

August 27 photo taken in UV light of a large, dark swath called a coronal hole, a region in the sun's corona or atmosphere where a high-speed solar wind blows outward into the solar system. Credit: NASA/SDO

If you’re out this evening and next and live in the northern U.S., Canada or the Scandinavian countries, keep an eye out for the northern lights. A stream of high speed electrons and protons flying out of large hole in the sun’s corona – a coronal hole – may spark some minor auroras.  Even if the aurora doesn’t show, go outside anyway and listen to the katydids while you watch the International Space Station make its final round of passes during the current window of evening visibility. It will appear as a brilliant “star” moving from west to east across the sky. All the remaining flybys for the Duluth, Minn. region are shown below. For times for your town, click over to Spaceweather satellite flybys or log on to Heavens Above.

* Tonight Aug. 28 starting at 9:33 p.m. Brilliant pass from the west across the southern sky. Watch it fade as it enters Earth’s shadow just below the bright star Altair in Aquila.
* Monday Aug. 29 at 8:35 p.m. straight across the top of the sky. Very bright!
* Tuesday Aug. 30 at 9:13 p.m. Fades into Earth’s shadow low in the south in Sagittarius.
* Wednesday Aug. 31 at 8:15 p.m. Bright, high pass in the south.
* Thursday Sept. 1 at 8:53 p.m. Low pass in the southwest
* Friday Sept. 2 at 7:54 p.m. Good pass across the south but happens around sunset. Will you see it?
* Saturday Sept. 3 at 8:33 p.m. Very low across the southwestern sky. Cruises just below the crescent moon at 8:35 p.m.

And finally, just a quick update on supernova 2011fe in M101, the Pinwheel Galaxy. Last night, the sky cleared off in time for me to spot it at magnitude 12.3. It was very easy to see in a 10-inch telescope. Click HERE for a page created by David Bishop devoted to the exploding star. And here are two maps to help observers with telescopes find the supernova.

How to find the new supernova in the Pinwheel Galaxy

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Find Mizar in the bend of the Dipper's Handle and then follow the little road of stars up to the Pinwheel Galaxy. The map shows the Handle as you face northwest at nightfall. Created with Stellarium

I’m very short on time just now, but wanted to take a few minutes to post a couple little maps to help telescope users find SN2011 fe, the new and bright supernova in M101 the Pinwheel Galaxy. Last night, it jumped another magnitude in brightness all the way up to magnitude 12.8 (my estimate). That’s great news, because now it’s within range of 6-inch and larger telescopes.

Face northwest at nightfall and find the Big Dipper. That’s easy enough. Then use the wide view chart to leap frog your way from Mizar, the star in the bend of the Dipper’s Handle, along the path shown to M101. The galaxy is visible in 40mm and 50mm binoculars as a smoky smudge from a dark sky site. It appears like a larger smudge with a brighter nucleus and faint spiral arms in a telescope.

My drawing is bit crude, but it'll get you there. Telescope users will easily see the star (a foreground star in the Milky Way) north of the nucleus. Shoot a line through it upward to the southwest and you'll go straight to the supernova. Illustration: Bob King

Once you’ve found the galaxy, bring your magnification up to around 100x and locate the fuzzy nucleus in the center of the galaxy. There’s a star on the north side of the nucleus. Draw a line from that star through the nucleus and keep going until you hit the very next star in that line — that’s the supernova! Depending on the size of your telescope, you may also see the two stars that flank the supernova. Both are dimmer than the supernova.

Good luck and let me know if you have any questions. The map at left is drawn to show the view in a typical reflecting telescope with south at top. I can’t wait to have another look tonight, when it should be brighter yet. For more information on the star, please scroll down to yesterday’s blog.

*** Click HERE for an updated supernova map (9/3)

 

Astronomers spinning over new supernova in the Pinwheel Galaxy

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At left is a "before" photo of M101, also called the Pinwheel Galaxy, with no supernova visible. At right is a picture taken with a 20" telescope on August 25 showing the new supernova. The new object is located southwest of the galaxy's core. Credit: Jim Misti (left), Joseph Brimacombe (right)

Wa-hoo! One of the closest supernovas in years was discovered at a very early stage in the bright galaxy M101,  the Pinwheel Galaxy, in Ursa Major. The galaxy can be found just above the Handle of the Big Dipper in the northwestern sky at the end of evening twilight. The supernova, dubbed PTF11kly, was discovered only two days ago by the Palomar Transient Factory, an automated wide-field sky survey looking for “optical transients” or things that pop up out unexpectedly like supernovae.

This map shows the sky facing northwest at the end of evening twilight. M101 is an 8th magnitude milky smudge above the end stars in the Handle. You'll need a 6-inch or larger telescope to see it well. You can use the closeup photo at top to navigate your way to the supernova. I'll provide a more detailed finder map tomorrow. Created with Stellarium

At discovery, the exploding star was very faint, but quickly rose in brightness. In just one night’s time, it shot from a dim 14.8 magnitude (Aug. 25) all the way up to 13.7 last night. That’s better than a full magnitude or a factor of 2 1/2.  Through my 15-inch scope, it was plainly visible.

While the supernova won’t become bright enough to see with the unaided eye, it almost certainly will be visible in small amateur telescopes within the next few days. That’s because the host galaxy is only 25 million light years from Earth — close by galaxy standards. With no moon in the sky for the next week or so, professional and amateur astronomers around the world will have PTF11kly in their crosshairs.

In a Type Ia supernova, a white dwarf (left) draws matter from a companion star until its mass hits a limit which leads to collapse and then explosion.

Since there’s more than one way for a star to explode, supernovae come in several varieties. This supernova in M101 is a Type Ia (one-a), a rather dry term describing one of the most catastrophic events in the universe. Here a superdense white dwarf, a star only about the size of Earth but with the gravitational power of a sun-size star, pulls hydrogen gas from a nearby companion down to its surface where it adds to the star’s weight. When the dwarf packs enough pounds to reach a mass 1.4 times that of the sun, it can no longer support itself. The star suddenly collapses in upon itself and detonates in an explosion that blows it to bits. What we see here on Earth is the sudden appearance of a brand new star within the galaxy’s disk. Of course, it’s not really a new star, but rather the end of one.

Artist's view of a white dwarf exploding as a supernova. Credit: ESO

You might recall the other bright supernova earlier this spring in the Whirlpool Galaxy not far from the Big Dipper. That one was a Type II variety, where a supergiant star runs out of nuclear fuel, collapses and then explodes. What’s unique about the Pinwheel Galaxy supernova was that it was caught in the very early stages.

Since most supernovae are in distant galaxies, we rarely get to see the start of a supernova event, because the star is too faint at the beginning of the explosion. Only when it’s well along, does it finally get bright enough to be picked up through a telescope.

M101 is practically a next door neighbor at just 25 million light years, allowing us to study a Type Ia supernova from almost the very start. Astronomers are eager for all the information they can get on this event to help them and us better understand the supernova process.  For more photos of the “new star”, check out Dave Bishop’s Latest Supernovae website.

See a star shrink and swell right before your eyes

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This chart shows the sky facing south around 9:30-10 p.m. Eta Aquilae is about one outstretched fist (8 degrees) almost due south of Altair in the bottom of the Summer Triangle. Two comparison stars are marked with their magnitudes. When Eta's at maximum, it equals the 3.4 magnitude star; when at minimum it's similar to the 4.5 star. Created with Stellarium.

Watching a star physically change in a matter of a week is something you’d think impossible to see. On the contrary. The star Eta Aquilae (AY-tuh AK-will-uh), located just down the block from the bright star Altair in the Summer Triangle, brightens up and then fades into the background every 7.17 days. And it does this with the precision of a fine watch.

I’ve kept my eye on it starting last Wednesday night, when it reached it greatest brightness of magnitude 3.5 (about a level fainter than the stars of the Big Dipper). By the weekend it had faded noticeably and finally bottomed out this past Monday and Tuesday at 4.3 or nearly a magnitude fainter. Last night the star quickly shot back up, and tonight will be shining again at its brightest.

The arrow points to the star Eta in the constellation Aquila the Eagle. The two photos show how the light of Eta changes over time due to changes in its size and temperature. The difference between minimum and maximum is much more apparent to the naked eye. Photos: Bob King

Eta is a yellow-white supergiant that shines 3400 times more brightly than the sun with a diameter 65 times larger. Too bad it wasn’t closer, or it would be one of the brightest stars in the sky. Its distance of 1170 years tames its light, so Eta looks like an ordinary star. Eta is a Cepheid (SEF-ee-id) variable star, named after the prototype Delta Cephei in the constellation Cepheus the King.

Simulation of the expansion and contraction cycle of a Cepheid variable star

Cepheids are unstable stars that pulsate in size, temperature and brightness. They shrink and expand right before our eyes! Naturally, because of the distance, we can’t see the star’s outer surface puffing out and sinking back in, but we know it’s happening by watching the star’s light and color change. Eta is brightest when it’s expanding the fastest and dimmest when it’s contracting the fastest. All this wonderfully visible instability has to do with the extremely hot temperatures in the star’s core. Most stars we see in the sky burn hydrogen as fuel to create energy; a Cepheid takes it to the next level by burning helium after it’s used up its hydrogen. This causes the star’s outer surface to rapidly expand until it overshoots a stable size, then shrink back – but a bit too far – which leads to another phase of expansion. In a sense, the star is trying to achieve a stable balance like the sun, but it can’t because of instabilities in its core due to helium burning.

Eta Aquilae was first recognized by the sharp-eyed English amateur astronomer Edward Pigott in 1784. It’s one of the brightest Cepheids known and a perfect one for beginning sky watchers to get acquainted with the wonders of variable stars. Tonight, watch for Eta to shine its brightest and then very slowly fade over the next several nights. By next Monday and Tuesday, it will be dimmest, then quickly return to maximum light Wednesday and Thursday. Amazing!

Moon and Mars meet face to face tomorrow morning

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This will be the view looking east tomorrow morning (Aug. 25) around 4 to 5 o'clock. Mars is still far from Earth but shining relatively brightly at magnitude 1.5. Maps created with Stellarium

Insomniacs and those rising early for work can look to the east tomorrow morning for a great view of the waning crescent moon and planet Mars. The two will be only about 3 degrees apart and form a very distinctive duo in the constellation Gemini the Twins.  They’re in good company. Orion and his famous 3-starred Belt are just an outstretched fist to the right, while further up you’ll find the equally striking Seven Sisters star cluster or Pleiades (PLEE-uh-deez).

Through a telescope, Mars is disappointing at the moment, because it’s too tiny to make out many features. Come this winter and next spring, our view will greatly improve as the Red Planet and Earth draw closer together.

Comet Garradd, now at magnitude 7.5 and visible in binoculars from a dark sky site, crosses through the little constellation Sagitta the next few nights, passing near the cluster M71. The cluster will be squarely inside the comet's tail on the 26th.

Another pairing of two celestial objects happens in the evening sky over the next several nights. The lovely Comet Garradd cruises by the globular cluster M71 in Sagitta the Arrow with closest approach happening on Friday the 26th. To find Sagitta, simply locate Altair, the bright star at the bottom apex of the Summer Triangle. One outstretched fist directly above Altair will take you to the Arrow.  A constellations go, Sagitta’s quite small – you can fit the whole thing in the field of view of many binoculars. Both comet and cluster will look like fuzzy patches of light.

M71 is a globular cluster in the Milky Way lying some 12,000 light years from Earth and measuring 27 light years across. At 6th magnitude, it's visible in binoculars from reasonably dark skies. Credti: Jim Misti

Telescopic observers will have the best view. Tomorrow and Friday nights, you’ll be able to see both Garradd and the globular cluster in the same low power field of view. The comet’s bright, pale green coma will contrast beautifully with the panoply of pinpoint stars that comprise M71.

The comet has been traveling across the northern summertime Milky Way this past week. That’s why recent photos show it against a background of countless stars. Two nights ago, I could just detect the pale green of cyanogen in the inner coma. The softly luminous tail, which now points to the southeast, was shot full of starlight. A fabulous sight!

Comet Garradd photographed Monday night (Aug. 22) through a 16-inch telescope with a 5-minute exposure. Credit: John Chumack

It’s a wonderful thing all these planets, the moon and comets that move about the solar system. By pointing the way, they save us the work of digging through star charts and maps to find other celestial sights. They remind me of some of the helpful people I meet every day.

Comet Elenin is fading; Doodlebugs on Mars?

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Pictures taken on Aug. 19 and 23 with the same equipment and exposure show how much the comet has faded in recent days. The photos were made with a standard camera lens and don't show the tail like 'deeper' images taken through a telescope. Credit: Rob Kaufman

The other day I wrote how unpredictable comets can be, one of the main reasons they’re so fun to follow by eye and telescope. After a nice show of steady brightening in the last few weeks, at least two dedicated comet observers – Michael Mattiazzo and Rob Kaufman in Australia – observed that C/2010 X1 Elenin has faded by about a full magnitude (a factor of 2 1/2) over the past several nights. Not good news, but not the end of the world either. Comets brighten and fade as “jets” of vaporizing ice entrained with dust turn on and off on its surface.

Animation of Comet Elenin from four pictures taken on Aug. 23 through an 11-inch telescope. Credit: Michael Mattiazzo

I’d rather it would continue to brighten toward a naked eye display this October when the comet’s closest to Earth. It still might, but it’s also possible that Elenin may fizzle out, especially if the fragile comet nucleus were to break into pieces.

Michael’s animation shows a slight elongation of the larger, bright nuclear region, the fuzzy, dusty area that hides the comet itself. Could it be an indication of a break up? We can’t be sure, but time will tell.  For all we know, Comet Elenin will return to its previous brightness expectations next week. For more photos and animations, I encourage you to visit Michael Mattiazzo’s Southern Comets Homepage.

As a kid, I remember discovering a doodlebug or antlion in the dirt along the side of a friend’s house. I watched as this insect larva with giant claw-like jaws waited at the bottom of its little sand trap for hapless ants to tumble down the steep sides literally into the jaws of death.  Tough world, but you gotta make a living.

An antlion sand trap. The insect waits beneath the hole with only its jaws sticking out. Credit: Wiki

This particular method of catching your food struck me as positively ingenious. Naturally we wanted to help out the antlion as well as watch the gruesome act of eating, so we looked around for random ants and dropped them along the “crater” rim, then pulled up close to wait for the inevitable. Anticipation can be a delicious emotion. Nature is always fascinating but especially through a child’s eyes. Children have an instinctive understanding of one nature’s universal principles: Eat or get eaten.

A skylight opening to an underground cavern in a small crater on Mars. Based on the shadow cast on the pit floor, the cave is about 65 feet deep. You can see how material has slid down the walls into the hole. Click to enlarge. Credit: NASA/JPL/University of Arizona

That’s why this recently released photo taken by the Mars Reconnaissance Orbiter of a crater with a hole in its center immediately brought to mind the antlion. I don’t mean to imply a real connection of course, but if you’re looking for a perfect setting for a science fiction story of alien antlions vs. humanity, this might be it.

The crater lies atop the slopes of the extinct Martian volcano Pavonis Mons, and the opening, which measures 115 feet across, is a skylight or entry to an underground cavern.

“Caves often form in volcanic regions like this when lava flows solidify on top, but keep flowing underneath their solid crust. These, now underground, rivers of lava can then drain away leaving the tube they flowed,” according to NASA writer Shane Byrne.

Later this year, the spacecraft will take another image of the cave from a slightly different angle to create a stereo pair that scientists hope will help them determine just how the hole formed. To see more photos of caves on Mars, click HERE.

Rock out under the space disco ball tonight

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Japan's high-tech disco ball, EGP, revolves around Earth every 116 minutes at an altitude of 900 miles. It's used to pinpoint remote Japanese islands and to study Earth's gravity field and motions of crustal plates. Credit: JAXA

In a Saturday Night Fever mood? Break out the medallions and your best polyester – we’re heading outdoors tonight to spot the 7-foot diameter orbiting disco ball called Hydrangea Flower (Ajisai in Japanese). Known better among satellite watcher by its more formal name – Experimental Geodetic Payload or EGP – this twinking “star” will amaze your eyes as you track it during a typical 18-minute long passage across the sky.

18 minutes is a long time compared to the approximately five minutes it takes for the space station to pass from horizon to horizon. That’s because EGP orbits Earth at an altitude of 900 miles versus the station’s approximately 230 mile orbit. Being farther from Earth, it moves more slowly through the sky.

EGP is a Japanese satellite launched in 1986 with a dual mission: to test a new launch vehicle and determine the exact positions of isolated and remote Japanese islands. And it really does look like a disco ball. The hollow sphere is covered in 318 mirrors and 1436 “cube corners” or retro-reflectors. Retro-reflectors are optical devices that reflect any light falling on them directly back in the direction from which it came. They’re used in everyday things like the insides of red tail-light covers on cars and bicycle reflectors. Even the paint on road signs contains reflectors in the form of tiny glass beads.

Scientists on the ground bounce a laser beam off one of the many mirrors or retro-reflectors on EGP and detect the return beam reflected back. Since the satellite’s orbit is exactly known, the round-trip return time for the beam will yield a location for the observer’s position on the ground accurate to millimeters. Satellite geodesy, as it’s known, is so accurate, it can detect the molasses-like movement of Earth’s crustal plates over short time scales.

A 35-second time exposure with a telephoto lens shows a series of flashes (some in groups of three) from EGP this past Saturday night as the satellite traveled through Draco the Dragon. As sunlight strikes the satellite's many mirrors, we see flashes of light. Details: 100mm lens, f/2.8, 35-seconds at ISO 1600. Photo: Bob King

Two nights ago I watched a pass of EGP. There’s nothing quite like it. With all those mirrors, the satellite flashes rapidly and irregularly like a string of firecrackers going off. The flashes were too faint to see with the naked eye – except from a dark sky site – but extremely easy in any pair of binoculars. The key to finding it is to use the simple maps available on the Heavens-Above satellite observing website.

Once you log on and select your city, look under the Satellites heading and click on Select another satellite. In the U.S. Space Command ID box, type in EGP’s ID number 16908 and click Submit. Clicking on the Ajisai (EGP) link takes you to a info page. At upper right, click on Passes (visible). Now just pick a convenient viewing time. There are many, since EGP is so high up it’s visible late into the night and early morning. I scanned the list of passes and selected the 22:09 (10:09 p.m.) pass tonight for Duluth, Minn. (see below).

For the Duluth, Minn. region tonight, the space disco ball will pass very close to Vega, one of the easiest-to-find bright stars in the sky. At the times shown, Vega will lie almost directly overhead. Created with Stellarium

When you click on the date link for the pass you’d like to see, you’ll be shown two maps. The top one is a wide view of the whole sky showing the entire length of the pass. The bottom one shows the brightest segment of the pass along with tick marks showing where EGP will be at particular times along its path. Pick a pass or a part of EGP’s path that takes it near a bright, easy-to-find star. Note the time when it’s near that star, then go outside five or 10 minutes before EGP’s arrival to let your eyes to get used to the dark.  A minute before it shows up, point your binoculars at your “guide star” and just wait. Pretty soon you’ll see it popping and flashing along.

While watching it Saturday, I counted about two strobe-like flashes per second. Twinkle, twinkle little star, indeed!