Andrew Kirk of Bishop, California, sent along this stunning photograph of lenticular clouds and iridescence (colored rings) taken on Tuesday the 28th. The clouds were very short-lived, evaporating in less than a minute.

Now that the snow’s gone, we don’t see quite as many animal tracks as we used to around my woods. Snow makes tracking easy but spring mud will work too. The most common prints in our region are made by white-tail deer, rabbits and small rodents. Can’t forget dogs and humans too.

Find the Three Leaps of the Gazelle between the Big Dipper and Leo the Lion. This map shows the sky tonight around 10 o’clock as you look high in south-southwest. If you lay on your back, you’ll find the view more comfortable. Created with Stellarium.

Although there are many animals depicted in the constellations, the most notable being Ursa Major, the Great Bear, there’s only one semi-official group of animal tracks up there. It’s a very cool pattern called the Leaps of the Gazelle, handed down to us from ancient Arabia. While not one of the 88 constellations, it’s notable because it really looks like prints a hoofed animal might make while gracefully leaping across the sky. According to the story, a gazelle was drinking water from a pond when it was surprised by Leo the Lion’s tail. The animal quickly jumped up and sprang to safety, leaving three neat prints in the sky.

To be truthful, the Leaps officially belong to the Great Bear; they represent the claws at the end of three of this legs. That works too but seeing them as animal tracks puts a little bounce into the sky.

The Leaps consist of three evenly-spaced pairs of modestly bright stars spread across 30 degrees or three outstretched fists of sky above the constellation of Leo. Take a look the next clear night and I think you’ll enjoy the symmetry of the pattern. It looks a lot like the more familiar deer tracks.

The Leaps are also part of the constellation of Ursa Major. Image from Urania’s Mirror, published 1825. (Gazelle photo above from photos.com)

Here’s how Earthshine works. Sunlight reflects off the blue and white Earth into space at the moon. The moon absorbs some and sends the rest back to us. We see this twice-reflected light as a dim illumination of the portion of the moon not lit by direct sunlight. Illustration, crescent and sun photos: Bob King; Earth image: NASA

Can’t get enough of that good old moonshine. Wait a second, I meant Earthshine. Our region’s been fortunate to have several clear nights in a row for watching this spooky light fill out the fattening crescent. I hope you’ve had a chance to see it too.

Last night during astronomy class, we talked about how late into the moon’s phase Earthshine might be visible. Years ago, I did an experiment using my 10-inch reflecting telescope and was able to see it when the moon was nine or ten days past new. More casually, I’ve seen it in binoculars when the moon was at half (first quarter phase).

This diagram shows the moon’s phase and the corresponding phase of the Earth as seen by someone on the moon. Notice that as the moon fills out, the Earth gets thinner. Illustration: Bob King; Earth and moon from Stellarium.

As the moon orbits the Earth, it marches upward from the sun while increasing in phase. As seen from the moon, the Earth also goes through phases that are complementary to the moon’s. When the moon’s a very thin crescent, an astronaut on its surface would look back toward our planet and see a nearly full Earth. A full Earth reflects a lot of sunlight back at the moon, so Earthshine is brightest when the crescent is thinnest.

As the moon’s phase increases toward first quarter and beyond, the Earth’s phase wanes, going from full to half to crescent. With less Earth to reflect sunlight, the Earthshine gets fainter and fainter. It also doesn’t help that the area for the Earth to illuminate shrinks as the sunlit portion of the moon grows ever larger night by night.

Our moon’s not the only one lit by its home planet. This is Saturn’s moon Iapetus photographed by the Cassini spacecraft. The right side is overexposed because it’s illuminated by the sun. The left side glows by light reflecting off Saturn’s clouds. Since sunlight is much fainter at Saturn’s distance than at Earth’s, Cassini had to make a long time exposure to capture this image. Credit: NASA

So now I’d like you to try a little experiment yourself. How many days after new moon can you still see the Earthshine — with your naked eye and also with binoculars? New moon was Friday April 24 which would make the moon five days old tonight (Weds.). Last night, the whole class saw the Earthshine easily without optical aid. As it becomes increasingly fainter in the coming nights, you’ll need to use averted vision to spot it. Look around and about the faint part of the moon instead of straight at it. Even better, hide the bright part of the moon behind a wall or power pole.

Drop me an e-mail and let me know how you fare. I’ll be out there drinking in my share of Earthshine too.

Lyle Anderson of Duluth sent this photo of the International Space Station he took from his home on Sunday at 4:42 a.m. (I added the annotations). The station’s been making regular pre-dawn passes over the U.S. this week. Check yesterday’s blog for times.

GRB 090423 as seen by NASA’s Swift satellite. Credit: NASA/Swift/Stefan Immler

I thought some of you might be interested in this bit of space news that just arrived in my e-mail:

NASA’s Swift satellite and an international team of astronomers have found a gamma-ray burst from a star that died when the universe was only 630 million years old — less than five percent of its present age. The event, dubbed GRB 090423, is the most distant cosmic explosion ever seen at 13.035 billion light years.
 

Bursts like these occur when a star runs out of nuclear fuel and collapses in upon itself, releasing huge amounts of energy in a supernova explosion. The burst happened early on the morning of April 23 and the news was just released today. Click here to learn more.

(Prepared from a NASA press release)

Chorus frogs, wood frogs and peepers. These are the company of a rural night. What a contrast to winter’s silence. A month ago I’d take off my hat to listen to the quiet at night’s end. The thump of my heart and occasional pop from a frozen tree constituted the entire soundscape. If I was really lucky, coyotes or wolves would call.

With April, the voices of night return. Woodfrogs cluck, peepers shriek and chorus frogs make a rhythmic crick that sounds like a finger running across the teeth of a comb. Add the shush of rushing water from a distant stream and it’s easy to set aside well-laid plans to track down this or that nebula. I find myself just looking up and absorbing without words.

Look west tonight (Tuesday) to find the moon, Mercury paired with the Pleiades and the V of the Hyades star cluster. This map shows the sky about 45 minutes after sunset or around 9 p.m. for Duluth, Minn. Maps created with Stellarium.

The moon was quite a showpiece last night what with its veiled Earthsine contrasting smartly with the brilliant crescent. According to a study by Project Earthshine, our planet is cloudier overall in April and May than in the other months. The more clouds, the more sunlight reflected off Earth and the brighter the Earthshine. Take a look tonight and see what you think. Their study shows the Earthlit moon is 10 percent brighter in spring.

Mercury and the Seven Sisters cluster in binoculars. Catch them tonight.

The regional forecast looks great for skywatching tonight. If you find a place with a clear view to the west and go out just before 9 o’clock, you’re in for a treat. Mercury will make a close approach to the Seven Sisters star cluster (Pleiades) low in the northwestern sky. The fast-footed planet will be the only bright star in the direction of the sun’s setting. The Pleiades will be faint with the naked eye but the view in binoculars will be worth the effort.

More advanced amateurs can watch the shadow of Saturn’s moon Titan sweep across the planet’s northern hemisphere tomorrow morning (Weds.) beginning at 1:23 a.m. Central time. You’ll need at least a 6-inch telescope or larger, high power and steady air to spot it. The further west you live, the higher Saturn will be in the sky and the greater your chances of observing the transit. Transits occur when a moon casts its shadow on the home planet below. From the perspective of someone living on the planet, they’d look up to see the sun covered by the moon and call it an eclipse.

The most recent transit of Titan was on April 13. You can see the orange-colored moon Titan at upper right in this short movie made from still photographs. Credit and copyright: Christopher Go

Titan is the second largest moon in the solar system so it’s shadow is visible in amateur scopes despite Saturn’s enormous distance from us. If you watch for Titan, go ahead and just stay up the whole night. That way you can wave good morning at the astronauts in the International Space Station when it flys by at 4:25 a.m.

Here are some ISS viewing times for the remainder of the week. The space station will travel from the west (or northwest) to the east across the northern sky.

Weds. April 29 beginning at 4:25 a.m.
Thurs. April 30 at 4:50 a.m.
Fri. May 1 at 3:43 and again at 5:17 a.m.
Sat. May 2 at 4:08 a.m
Sun. May 3 at 4:34 a.m.

V is for Virgo! Or should I say vertigo. Sometimes you can look so long at the sky, you think you might fall in. And if you’re going to fall, Virgo’s the place to do it because the sky’s deeper there than just about anywhere. How is that? Virgo is far removed from the hazy band of the Milky Way with all its dust clouds, nebulas and blizzards of stars. That stuff just gets in the way and blocks the light of galaxies beyond. Look in Virgo’s direction and you’ll gaze straight up and out of the Milky Way into deep space. To the eye, Virgo looks sparse, but a telescope reveals hundreds of galaxies in all that emptiness.

If you can spot Spica, you’re halfway to finding Virgo. Connect Spica to the "V" or cup of stars above it, and you’ve found the brightest part of the constellation. Created with Stellarium.

We’ve touched on Spica before, Virgo’s brightest star, but haven’t connected the stars around it to form the constellation itself. Virgo the Virgin is one of the twelve constellations of the zodiac and the second largest in the sky. You can find Spica in at least two ways: follow the arc of the Big Dipper’s Handle to the brilliant orange star Arcturus and then continue the arc downward to the next bright star. That would be Spica. Or you can start at Regulus in Leo, which is due south at nightfall and a little more than halfway between the southern horizon and the overhead point. Shoot a line from Regulus to Saturn and continue on to Spica.

Once you’ve found Spica, look about a fist and a half above it for a broad cup of stars roughly in the shape of the letter V. Spica and the V form the most prominent part of the Virgin. The stars in the V are about as bright as the dimmer ones in Leo’s outline.

A small section in the center of the Virgo Cluster shows at least two dozen fuzzy galaxies. Credit: Digitized Sky Survey, Palomar Observatory, STScI

Within the V and near it are some 2000 galaxies, all members of what’s called the Virgo Cluster, a grand gathering of galaxies buzzing around together at a distance of some 60 million light years. We’ve discussed star clusters on many occasions in this blog. The Virgo Cluster is the next level up — a cluster of galaxies. Not only that, but the gravity exerted by so many galaxies is felt even in our own neighborhood.

This diagram, which is centered on our Local Group and Milky Way, shows a small sampling of the galaxy clusters in our neighborhood. The Virgo Cluster is right of center. Credit: Richard Powell

The Milky Way belongs to a much smaller cluster of galaxies called the Local Group. Our group, along with at least 100 others, is gravitationally bound to Virgo. Where it goes, we follow. Put the whole shebang together and you’ve got what astronomers call the Local Supercluster. It’s about 110 million light years across and one of a myriad of superclusters in the universe.

I’m now nearly out of breath, ready to fall into Virgo’s deeps. So much space, so much time. Someone please take hold of my hand.

I hope you saw the youthful moon last night. One observer left a nice report in the Comments section of yesterday’s blog. Because of another commitment I wasn’t able to see the moon but did catch Mercury just after 9 o’clock in the northwestern sky. It was very easy to see. Alas, the moon was too close to the horizon at the time and hidden anyway by a swatch of cirrus.

See the trio of moon, Mercury and the Pleiades tonight (Sunday) starting about a half-hour to 45 minutes after sunset. This map shows the sky as you look northwest around 9 p.m. Maps created with Stellarium.

Tonight promises to be another good one for moon and Mercury watching. The moon moves about one outstretched fist to the east (left) and upward each night, putting it comfortably above Mercury Sunday night. Joining the gathering will be the Seven Sisters (Pleiades) star cluster. While the cluster will appear faint, the moon and Mercury should be easy catches. Bring your binoculars to see all three at their best.

Mercury often appears pink when seen at twilight. When I was a kid, I remember thinking it was because the planet was really hot being so close to the sun. You may notice this too as you examine it with you eye. Truth is, it takes on the ruddy color of dusk. If you were to track down the planet during the daytime with a telescope, you’d see it as ordinary white, similar to the moon or Venus.

Mercury also has phases like our moon. Right now it’s a very tiny crescent that requires a telescope to see. Since we normally look at Mercury very low in twilight, the thick air at that elevation distorts and mushes out the image. That’s why some amateur astronomers choose instead to observe it during the day, when the planet’s much higher up and less disturbed by our roiling atmosphere.

See a planet in the daytime? Yes. The easiest way to do this is with one of those computerized telescopes, where you punch a button and the scope slews to its target. I don’t have one of these so I do it the hard way by plotting the planet’s position relative to the sun and moving the scope by hand. What can I say, it’s good exercise.

The supernova in NGC 4088 (NGC stands for New General Catalog) is near the Bowl of the Big Dipper. Here’s another picture of the galaxy. Photo credit: William Wiethoff

I spent much of the night observing comets and a pretty supernova in a galaxy called NGC 4088 in the Dipper. The supernova exploded 45 million years ago (the galaxy’s distance from us) but its light only finally arrived on Earth earlier this month. While a supernova looks just like a star superimposed on a galaxy, you have to remember that tucked into that faint point of light is the titantic explosion of a supergiant star at the end of its life. This one, called SN 2009dd, is smack dab on NGC 4088′s central core and bright enough to see in an 8-inch telescope from a dark sky. William Wiethoff of Port Wing was out last night too, and sent along the photo he took of the supernova. Gorgeous is all I can say.

The galaxy M102 (top) shows a thin lane of dust across its middle. Our galaxy the Milky Way shows a similar lane silhouetted along its length (below). Since we’re sitting right inside our galaxy, the Milky Way’s dust lane shows much more detail and texture. Photos: top, Will Wiethoff, bottom: Bob King

Will also photographed another galaxy called M102 in the constellation Draco the Dragon. Notice the dark line bisecting the glowing disk. We see this galaxy from the side or "edge on". From this perspective, stardust within the galaxy’s disk is silhouetted against billions of stars and appears as a dark lane. The same stardust is visible along the length of the Milky Way galaxy, where it looks like dark blotches among the bright starclouds. Much of this dust originates from the remains of exploding stars just like the one in NGC 4088. There’s poetry in that.

The moon never fails to delight. Three mornings ago, it passed in front of Venus; tonight it offers skywatchers a perfect opportunity to see one of the thinnest crescents ever. The moon’s age is determined by how many hours or days have passed since new moon. You might recall that you can’t see a new moon because it lies in the same direction as the sun. Sure the moon’s there, but the glare of sun and sky make it impossible to see. We have to wait almost a day for the moon’s motion to carry it far enough away from the sun for the first crescent to be visible.

The moon will be only 6/10ths of a percent lit this evening when it becomes visible about a half hour after sunset (8:45 p.m. for n. Minn/Wisc) in the northwestern sky. Look very low above the sunset point with your naked eye or binoculars to find it. The planet Mercury lies just a few "fingers" above and to the left of the moon. Created with Stellarium.

New moon happened last night at 10:22 p.m. Central time. A half-hour after sunset tonight (Saturday) — or some 22 hours after new moon — an exceedingly delicate crescent will hover over the sunset point during early twilight. If you live in the eastern U.S., the moon will be only 21 hours old; 23 hours in the mountain states and 24 hours for the West Coast.

Most of us can spot a two-day old moon with ease but one less than a day old takes a little planning. Here’s what you’ll need:

1. A clear sky without haze
2. An unobstructed view to the west
3. A clock so you can be on time

Take your binoculars along too. They can help you spot the moon before you see it with your naked eye. That way you’ll know exactly where to look. Once you find the moon, look closely at the wire-thin crescent. Is is smooth along its length or uneven? I’ve noticed in crescents past that some parts look broken or choppy. Remember that the sun is just rising along the edge of the crescent and that shadows at sunrise are very long. Shadows cast by crater walls and mountains slash straight across the thin crescent, breaking it in places.

This photo, made on April 5, 2008 by the Japanese Kaguya spacecraft in orbit around the moon, shows the colorful Earth rising above the grey lunar landscape. When we see the moon as a thin crescent, astronauts on the moon would see the Earth in "full" phase, just as in this photo. Moon and Earth phases are exactly complementary. Credit: JAXA 

As the sky darkens a bit, you might also see the full outline of the moon. This dusky light is called Earthshine and is caused by sunlight reflecting off our own planet back at the moon. Can you discern any dark shapes within the Earthlit portion? Those are the lunar "seas" (volcanic plains) that form the face of "the man in moon" that we see with ease during full moon phase.

As with every human endeavor, there are those who love to push the limits. When it comes to young moons, American Stephen James O’Meara holds the naked eye record with his sighting of a crescent only 15 hours 32 minutes old in May 1990. The youngest crescent observation with optical aid was made by Mohsen G. Mirsaeed of Tehran, Iran on September 7, 2002 when the moon was 11 hours 40 minutes old. Since Western Europe is 5-6 hours ahead of U.S. time, observers there could challenge the naked eye record tonight.

There’s even a bonus for anyone who goes out to look. Shining just above the moon is Mercury, one of the solar system’s more elusive planets. It never gets far from the sun so never escapes the twilight glow. With the moon as your guide, I’m confident some of you will see this little world for the first time. Have fun this evening.

Earthrise as seen from the moon photographed by astronaut Ronald Evans during the Apollo 17 mission in 1972. Can you guess what the moon’s phase was when this photo was taken? Credit: NASA

Cloud to cloud lightning, the most common form, sparks in this storm cloud over Carlton County last night. Details: 70mm lens at f/5.6, 30 second time exposure at ISO 400. Photo: Bob King

Lightning flashing near the horizon last night evoking memories of summer, fireflys and humid air. Some of the flashes were bright enough to cast sudden shadows and even catch the attention of those watching TV indoors. Tempted by the display, I sought a wide open space to take in the show. Though the storm was miles away and soundless, the lightning within the clouds was spectacular.

Lightning is nature’s attempt to come back to equilibrium. In the tortuous updrafts and downdrafts within the storm clouds, regions of negative and positive charge build up. Typically the bottom of the cloud is negatively charged, the top positive. If the difference between two is large enough, they’ll seek each other out and neutralize in one gigantic spark of lightning. Have you ever scooted around in socks on carpet and then touched a metal doorknob? It’s the same principle. The rubbing builds up an excess of negative charge. Once you’re close enough to the knob, a spark jumps the gap and gives you a little zap.

Charges within the cloud and between the cloud and Earth build up to high levels because the atmosphere is an excellent insulator. The negative and positive electrical regions want to zap together as soon as possible, but the air keeps them apart until the difference between them is so huge, something has to give. As a storm cloud moves over the ground, its negatively charged bottom induces the ground beneath it to become more and more positively charged until the two connect in a stroke of lightning.

The white-hot star Rigel, shown with starspots, is the brightest star in the constellation Orion. It surface temperature of 36,000 degrees Fahrenheit is very similar to that of lightning. Rigel is 775 light years away and shines with the light of 40,000 suns. Credit: FrancescoA

Lightning is typically about 1-inch in diameter and about one to five miles long. Some bolts are much longer. The record was an 118 mile long bolt in the Dallas-Ft. Worth area. The temperature of lightning is around 50,000 degrees Fahrenheit — five times hotter than the surface of the sun! Lightning momentarily heats the air around it to 18,000 degrees, creating the shockwave of sound we hear as thunder. To learn more about lightning, check out this page on NOAA’s National Severe Storms Laboratory website on NASA’s lightning page.

If you were to seek a star in the sky as hot as lightning, you’d to pass most of them up. Only a small fraction of stars — the blue and white supergiants and white dwarfs — are in lightning’s heat class. White dwarfs are extremely tiny, and none are visible without a telescope. Blue supergiants on the other hand are some of the brightest stars in the galaxy. Luckily, they’re well represented in the departing winter constellation of Orion the Hunter.

Catch Orion in the next week or so before it’s too low in the west. All three Belt stars have surface temperatures between 50-60,000 degrees. Created with Stellarium.

On the next clear night, give a glance in the west during evening twilight and see if you can still find Orion’s Belt and the star Rigel beneath. These four luminaries all have surface temperatures in the 35,000-60,000 degree range and blaze like spheres of nonstop lightning.

It’s amazing to think that right here on Earth we can experience, however briefly, the fearsome power of the largest stars. 

For early risers, here’s a listing of times and directions for viewing the International Space Station beginning tomorrow morning the 24th. Watch for a very bright moving "star" rising up from the west and traveling eastward (in most cases). If you live outside the region, click here and fill in your zipcode to get accurate times.

Friday April 24 — a brilliant, nearly overhead pass starting at 5:23 a.m. The ISS will "rise" in the west and travel toward the northeast.

Sat. April 25 – starting 4:16 a.m. / southeast to northeast.

Sun. April 26 — 4:41 a.m. / west-soutwest to east-northeast. Another high, bright pass.

Mon. April 27 — 5:06 a.m. from west to east-northeast

Tues. April 28 — 4 a.m. This one starts way high up in the west and fades out in the northeast. Brilliant pass! A second pass at 5:33 a.m. from west-northwest to east-northeast.

The Milky Way spans the eastern sky yesterday morning before dawn. Details: 16mm lens at f/2.8, 30-second time exposure at ISO 1600. Photos: Bob King

Yesterday morning before the moon-Venus excitement, I stood for a while looking up at the Milky Way. While the spring constellations hold sway during the evening hours, the ever-turning Earth finally brings the summer stars around when most of us are sleeping. With summer comes the splendour of our galaxy. It billows across the sky from Cassiopeia in the northeast to Sagittarius in the far south. Among the hundreds of stars that spangle its length are the familiar bright ones of the Summer Triangle.

When we look into that milky band, we’re peering straight through the thickest part of our galaxy’s flattened disk. The stars stack up in the distance until their light blends together into a soft, unresolved glow. Telescopes resolve the Milky Way into individual stars and star clusters, but our unaided eye is innocent to this fact. That’s why no one knew for sure what the Milky Way was until Galileo first pointed his homemade scope at it 399 years ago.

Students from the area spend time before the concert talking and visiting.

This morning I stood in the Duluth Auditorium before a throng of school kids who came to listen to a short classical music concert. Before the music started, the place was filled with the sounds of their voices eagerly talking and laughing. All that chattering energy ultimately finds its source in atoms and molecules forged over billions of years in the interiors of the early stars. Those simple bits came together in our corner of the universe to form the sun and planets. Some 7 1/2 billion years after the Big Bang, our planet rolled Lucky Sevens and life took hold from crust to atmosphere with fruitful vengeance.

If stars could talk, would they sound like those kids waiting for the music to begin? Absolutely.