Did distant comets quench a thirsty Earth?

A striking active prominence issues from the big sunspot group 1305 as it approached the western limb of the sun last Thursday. Prominences are towering flames of incandescent hydrogen gas many thousands of miles long often associated with sunspot groups. Credit: John Chumack

A beautiful, bright sun shines outside my window this morning. It was preceded by the setting moon and the onset of dawn, both of which I saw while hunting for Comet Elenin. In the briefest of intervals, I watched the sky go dark around 5:45 a.m. and then the lights slowly come back up with twilight after six. Try as I might however, I couldn’t convince myself of seeing the comet through the big 15-inch scope. Maybe there was a bit of fuzz there, maybe not. I used low power, medium power and even the power of imagination but nothing I tried convinced me Elenin was there. I’ll be out again around the 23rd or 24th when conditions will be much better. Until then, happy trails Comet E!

Comet Hartley 2 photographed by the Deep Space/EPOXI spacecraft in 2010. Credit: NASA

Last week European astronomers using the Herschel Space Observatory announced they’d found water in Comet Hartley 2 with almost the same composition of water found in the Earth’s oceans. You might remember Hartley 2 which passed near Earth in October 2010 and became faintly visible with the naked eye for a time. It was also the target of a close flyby by the Deep Impact mission a month later.

The question of where our planet got all its water has been hotly debated. The Earth grew over a period of 1-200 million years 4.3-4.5 billion years from the accumulation of millions of meteorites and asteroids. Heat arising from all that impacting material and the decay of radioactive elements (which release heat energy) melted our little globe, causing the heavier metals like iron and nickel to sink to the core with lighter rocks floating to the top to form the planet’s crust. Our world was once a glowing ball of hot magma – not exactly the kind of place you’d find water sloshing about.

That’s why scientists believe the water that’s now so plentiful and makes our world so distinctive had to be ‘delivered’ later after things cooled down. Since comets are composed largely of water ice and there are billions of them – especially in the early solar system when there was so much more ‘junk’ around – they seemed the perfect choice as a delivery mechanism to quench our planet’s thirst.

A neutron (in blue) joins hydrogen's single proton to make deuterium, represented by the chemical formula 2H.

One problem: almost all comets astronomers have studied so far contain twice as much deuterium in the hydrogen that makes the H in their H2O. Deuterium? The most common form of hydrogen has only one proton in its nucleus circled by a single electron, but 1 out of 6,420 hydrogen atoms in the Earth’s oceans also has a neutron paired up with that proton. The addition of the neutron doubles the mass of the hydrogen which is why D2O (D for deuterium) is nicknamed ‘heavy water’. If comets really are responsible for bringing water to Earth, why don’t our oceans have more heavy water? Enter the European Space Agency’s Herschel Space Observatory, the largest space-based scope currently in orbit. Its 138-inch (3.5 meter) diameter mirror and optical system are optimized to study the sky in infrared light.

This illustration shows the orbit of Comet Hartley 2 in relation to those of the five innermost planets. The comet made its latest close pass of Earth in October 2010, at which time Herschel observed the comet. Water shows as a big blue bump in the comet's light spectrum (right). Credits: ESA/AOES Medialab; Herschel/HssO Consortium

Herschel studied Comet Hartley 2 and discovered that its water has almost the same composition – regular vs. heavy water – as the Earth’s oceans. Most of the comets previously studied are thought to have formed closer to Jupiter and Saturn and then booted into the outer solar system’s Kuiper Belt through gravitational interactions with those planets. Comet Hartley 2 is different. Its birthplace was the frigid Kuiper Belt, where the deuterium to hydrogen ratio may have been very different from the one in comets formed closer to the sun.

Beyond the orbit of the most distant planet Neptune lies a vast region populated by icy asteroids and comets called the Kuiper Belt. Comets like Hartley 2 are believed to have formed here 4.5 billion years ago. Later some of them migrated inwards and may have collided with Earth, delivering water to the early planet's parched surface. Credits: ESA/AOES Medialab

So the water that makes our planet the wettest, wildest place in the solar system may still have come from comets, but from ones formed in the far reaches of the solar system. Astronomers using the Herschel scope will now be looking at other comets to confirm their hypothesis.

Comet Hartley 2 leaves a trail of fluffy snowballs

Comet Hartley 2 as seen by WISE. Data from the infrared telescope revealed that the comet's trail, seen here as the long, thin yellow line, consists of particles as large as golf balls. Image credit: NASA/JPL-Caltech/UCLA

Recent photos taken NASA’s Wide-field Infrared Survey Explorer or WISE has revealed that Comet Hartley 2 is dropping golf-ball sized fluffy ice balls in its wake as it orbits the sun. Dust following in the wakes of comets isn’t new, but scientists were surprised to see that the pieces seen close up by the EPOXI spacecraft last year survived long enough to give the comet a ‘bumpy’ trail.

Although Earth isn’t expected to cross through Hartley 2’s debris trail anytime soon, our passage through the trails of other comets produce some of our favorite meteor showers like the summer Perseids and winter Geminids. Perhaps someday our orbits will ‘cross paths in the night’ and if we’re lucky, a few persistent snowballs might create a jaw-dropping fireball meteor or two.

Cassiopeia the Queen is on the rise again during the second half of July at nightfall. Look for this celestial W in the northeastern sky. Created with Stellarium

Last night the moon was full and sky hazy, but our group could still make out the familiar W of Cassiopeia up in the northeastern sky. The time was around 11 p.m., and we were standing out on a dock over Boulder Lake north of Duluth taking in the moonlight and the loon calls. Lovely night. Although fall’s still a ways off, the Big W is a reminder of the season that’s waiting in the wings.

Our group was participating in the Experience the Night program that started at 8:30 p.m. and wrapped up this morning at 6. Several people spoke on night-related topics in their area of expertise, so we had a spider expert, a University of Minnesota etymologist, a birder and an astronomy guy (yours truly). The passion of others, whether for moths, glowing fungi or frogs, always helps us to appreciate the creative abandon of nature.

Moon brews up a little earthshine tonight

Look to the left of the sunset direction to spot the 3-day-old crescent moon during evening twilight. Created with Stellarium

With Daylight Saving Time out of the way, you probably noticed how early the sun went down yesterday evening. Around here, it’s gone by 4:45 p.m., and night begins at 6:30. That’s great for getting out early to see things like the space station – there’s a pass at 5:16 p.m. today – as well as a newly-minted crescent moon. To find the moon tonight, face southwest 20-30 minutes after sunset or around 5:15  p.m. for the Duluth, Minn. region. The sky might be dark enough, depending where you live, to see the dark, dimly-lit portion of the moon nicknamed “the old moon in the new moon’s arms.” Sunlight reflected off the Earth’s oceans and clouds lights the part of the moon not directly illuminated by the sun and is reflected back to us in turn. This twice-reflected light is called earthshine; its bluish-gray in color and ghostly compared to the bright sunlit crescent. The view through binoculars of the earthlit moon is even more amazing than with the naked eye alone. Take a look and see for yourself.

An unpiloted ISS Progress resupply vehicle approaches the International Space Station, bringing to the orbiting complex 1,918 pounds of propellant, 1,100 pounds of oxygen, 498 pounds of water and 2,804 pounds of food, spare parts, experiment hardware and other supplies for the Expedition 25 crew members. Credit: NASA

While the Discovery shuttle launch has been delayed until the end of the month for repairs, the space station keeps whirling overhead during evening hours the whole week long. Here are viewing times for the Duluth region. For times for your town, click HERE and enter your zip code or visit Heavens Above.

Except where noted, most of the passes will be across the northern sky with the station moving from west to east. Several of them will be exceptionally bright!

* Tonight starting at 5:16 p.m.
* Tues. Nov. 9 at 5:42 p.m. Very bright, reaching magnitude -3.  This space station will slice through the Handle of the Big Dipper and then pass under the North Star.
* Weds. Nov. 10 at 6:08 p.m. Comes up from the northwest and passes directly overhead where it will reach -3.7 magnitude (!) Watch as the station suddenly fades from view high in the southeastern sky. Binoculars will show its color changing from yellow to sunset red.
* Thurs. Nov. 11 at 4:59 p.m. in bright twilight across the north. A second pass across the western sky will take place at 6:34 p.m.
* Fri. Nov. 12 at 5:25 p.m. Brilliant -3.7 magnitude pass from northwest to southeast that goes straight overhead. Best of the week.
* Sat. Nov. 13 at 5:51 p.m. across the southwest-southern sky. Passes right under the moon near the end of its track.

I thought you’d like this great animation sequence of last week’s flyby of Comet Hartley 2 by the Deep Impact probe. It combines 40 frames taken during the encounter by the spacecraft’s Medium-Resolution camera. The first image was taken at about 37 minutes before the time of closest approach at a distance of about 17,000 miles. The last image was taken 30 minutes after closest approach at a distance of 13,800 miles. The spacecraft was able to photograph nearly 50 percent of the comet’s illuminated surface in detail.

Animation showing changes in Comet Ikeya-Murakami over four days. Credit: Ernesto Guido & Giovanni Sostero

How about another excellent comet animation? This one is of Comet Ikeya-Murakami and created from multiple exposures taken between November 4 and 8 by Italian amateur astronomers Ernesto Guido and Giovanni Sostero. It appears the comet was discovered during an outburst, when it quickly rose to visibility as fresh ice was exposed or released through jets from its surface or fissures deeper down. Outbursts inevitably fade; indeed the comet already appears to be dimming some. I hope our telescopic observers will have an opportunity to see it. Here’s the chart once again to help get you there.

Can’t seem to shake off this comet dust

A fingernail moon pokes out from behind bare branches during twilight Thursday morning. Photo: Bob King

With our attention focused on Comet Hartley 2 yesterday, I forgot all about Thursday morning’s crescent moon. OK, I should have arisen earlier when the moon was even more striking in a darker sky, but the sight was refreshing nonetheless. I hope you saw it. Tonight the moon is new and will return as a waxing crescent in the evening sky next week.

Getting up for morning sky watching has been somewhat less painful than usual this month. With Daylight Saving Time now extending into the first week of November, our region will experience its latest sunrise in a long, long time tomorrow – 7:59 a.m. That’s about 10 minutes later than the usual latest sunrise, which occurs in late December. On December 29, the sun comes up about 7:51 a.m. Central Standard Time. If our legislators were to extend daylight time to the end of the year, that sunrise would instead be 8:51 a.m.! Heck, I’d get up every clear morning and poke around the sky before breakfast. One last note about time: don’t forget, this is the weekend we return to standard time. Set your clocks back an hour Saturday night and enjoy the extra snooze time Sunday.

This image montage shows comet Hartley 2 as NASA's EPOXI mission approached and flew under the comet. The images progress in time clockwise, starting at the top left. All comet photos: NASA/JPL-Caltech/UMD

When it’s all said and done, some 120,000 photos will be taken of Comet Hartley 2 by the Epoxi mission, but those first five are simply amazing. When I observed the comet this morning and saw its big, glowing coma, all I could think about were those spectacular jets spewing dust and vapor. As the nucleus rotates end over end in the span of about 18 hours, the jets charge the space around the comet’s nucleus with a temporary atmosphere. I also felt appreciation for the efforts of the people who engineered the Deep Impact probe and got it to its second comet after years of planning and orbital maneuvering. Thanks to the ingenuity of our fellow humans, we can understand and participate in one of nature’s grandest if ephemeral creations – a comet.

This enhanced image, one of the closest taken of comet Hartley 2 by NASA's EPOXI mission, shows jets and where they originate from the surface. There are jets outgassing from the sunward side, the night side, and along the terminator -- the line between the two sides.

Check those geysers out in the photo above. You might wonder if all those gassy jets can propel the comet off its path. After all, according to Isaac Newton, every action has an equal and opposite reaction. While this is certainly true, the gas escaping from a comet has so little mass in comparison to the solid mass of the comet itself, the nucleus is affected very little. Over time however, certain comets with large, active jets do show shifts in their orbits, in part because of the “push-back” effect or what astronomers call non-gravitational forces. These accumulate to change the period of the comet’s orbit or how long it takes to go around the sun. It was first noticed in Comet Encke, which at 3.3 years has the shortest period known of any comet. After many returns, comets eventually degrade and lose most of their ice. They come to resemble dark-crusted asteroids and look like tail-less faint stars, their glory days now over.

This montage shows the only five comets imaged up close with the EPOXI mission spacecraft. The comets vary in shape and size. Comet Hartley 2 is by far the smallest and the most active of small comets. This jet activity can be seen extending from the comet's surface and into its outer shell of gas and dust, or coma

As twilight swelled this morning, I pointed the telescope at newly-discovered Comet V1 (Ikeya-Murakami) in Virgo. It was much smaller than Hartley 2 but every bit as charming in that misty way that comets are. Now that astronomers have calculated a preliminary orbit, I’ll roll out a chart for tomorrow’s blog. Butterscotch-hued Saturn is now up high enough by 6:30 a.m. to find and observe easily in a small telescope. The rings are tipped open considerably more than last year and will guarantee to elicit oohs and aahs if you’re willing to part with a little sleep.

The scary side of night

The Witch Head Nebula, also known as IC 2118, is a faint cloud of interstellar dust in Eridanus illuminated by nearby Rigel, which is off the frame to the right. Can you see her nose, eye and mouth? Click on the photo for hi-res image. Credit: NASA/STScI Digitized Sky Survey/Noel Carboni

Today’s Halloween, a time to celebrate the night if there ever was one. I hope you’ll be out treating, tricking, handing out candy and otherwise reveling in the fun. The sky has its scary side, too. Things like the Owl Nebula, the Cat’s Eye , the Ghost of Jupiter and even a Medusa Nebula adorn its dark underbelly. One of my favorites is the Witch Head Nebula in Eridanus the River. You’ll find it just west of Orion’s brightest star, Rigel, located in the lower right corner of his rectangular outline.

The Witch Head is a 50-light-year long interstellar dust cloud some 900 light years from Earth. The blue color is caused both by the bluish light from Rigel, a very hot white supergiant, and the fact that the tiny grains composing the cloud reflect the shorter wavelengths of blue better than red. The dust grains are very similar in size to the wavelength of blue light (475 billionths of a meter). which is scattered by very tiny particles more than the greens, oranges and reds which pass on through the cloud and continue on their way. Both the sky and a cloud of cigarette haze appears blue for the same reason.

Ghostly blue Comet Hartley 2 plies the star fields of southern Gemini early this morning. The tree in the foreground is blurred because I tracked the comet during the exposure. Details: 200mm lens, f/2.8, ISO 800 and 2-minute exposure. Photo: Bob King

Speaking of ghostly things, I looked up Comet Hartley 2 last night once it cleared the trees around midnight. It was easy if faint in 8×40 binoculars and still looked like a huge powder puff in the telescope with a brighter spot at center. The comet is slowly moving away from both Earth and sun, and will gradually become fainter through the month of November.

As sunspot group 1117 rotated across the sun's face, it evolved from a single spot to a large and complex group. Sunspots are regions on the sun's surface where intense magnetism welling up from below cool the surface in the form of dark spots. This areas of concentrated magnetic energy sometimes erupt with solar flares. The sun rotates once on its axis about every 27 days. Credit: NASA/SDO

The past week and a half has a been good one for watching the evolution of sunspot group 1117. It made its first appearance around October 19 on the sun’s northeastern limb as a single spot. Within a week it developed into several planet-sized sunspots huddled together in a triangular formation. Today it’s near the sun’s northwestern edge; by tomorrow or the next day, the sun’s rotation will have moved it out of view to the backside. Before bidding us adieu, the region kicked out a couple nice flares this morning.

The still images give you a feel for the increasing complexity of the group, but for the real fun, go to the Solar Dynamics Observatory website data page and see the movie. Here’s how to do it:

1. Click on Browse by Date Range and enter 2010-10-21 to 2010-10-31 or choose from the calendar.
2. Select AIA4500 from the drop down menu. This will show the normal, white-light photos. If you want to see the sun in other wavelengths, many choices are available.
3. Click the Movie button and then Submit.
4. Let the images load, then sit back and marvel.

Bowling for comets and Jupiter gets freckles

Twelve radar images of the nucleus of comet Hartley 2 were obtained by the Arecibo Observatory's planetary radar from Oct 25 to 27, 2010. Image credit: NAIC-Arecibo/Harmon-Nolan

Deep inside the big, fuzzy glow of Comet Hartley 2, astronomers have spied its nucleus for the first time using the Arecibo radio telescope in Puerto Rico. The core of the comet looks something like a bowling pin except that it’s 1.4 miles long. Jets of icy vapors and dust emanating from cracks on the comet’s surface create a glowing cloud around the nucleus that we see as a fuzzball in our binoculars. The images above show that the comet is spinning, rotating end-over-end once every 18 hours.

The eerie-looking images were made by bouncing radio waves off the comet’s surface around the time of its closest approach to Earth. Returning waves arrive at slightly different times depending upon the contours of the comet’s surface. Scientists turn those time differences into a crude image. For a more detailed explanation, check out this blog by the Planetary Society’s Emily Lakdawalla. Though the pictures show only the grossest details, they whet our appetite for the closeups soon to come when NASA’s rejiggered EPOXI probe flies only 435 miles from Hartley 2’s core next Thursday. Stay tuned!

This chart shows the sky as you face east around 12:30-1 a.m. in the upcoming week and a half. Comet Hartley 2 should still be very obvious in binoculars from darker suburban and rural sites. This and the Jupiter diagram created with Chris Marriott's SkyMap software

With the moon now rising in the morning hours and waning all the while, the comet is once again an easy catch in the east. I’m sorry to say you’ll have to be out late to see it. The map above shows the sky when no moon is up. Hartley 2 will be traveling southeast through Gemini the Twins into Canis Major the Little Dog. For a more detailed chart, click HERE.

We're fortunate to have another double shadow transit of Europa and Ganymede tonight. Their shadows will be nearly lined up.

Did you catch the double shadow transit of Ganymede and Europa on Jupiter last Saturday? If you didn’t because of poor weather or other commitments, you’ve got another chance tonight when the two will be back at it again. Ganymede’s shadow makes its first appearance along the eastern edge of the planet at 11:10 p.m. Central Daylight Time; Europa follows only six minutes later. By 11:30, they both should be obvious black dots. The diagram above shows the planet with south up, the way it’s oriented in most telescopes. Europa itself will be in front of the planet and very difficult to see. Ganymede will have moved off the disk and shine brightly to the west.

In search of the Lord of the Rings

Look for Saturn about 6 degrees above the eastern horizon during morning twilight. That's about three fingers held out horizontally at the end of your outstretched arm. Created with Stellarium

Last week my friend Eric asked when Saturn would return to the morning sky. He missed the planet and felt a lack of “ring time” in his life. I know how it is. Jupiter’s been spectacular this season, but like Eric, I’m itching to see what the rings are up to. They’ve been close to edgewise the past year and a half but will finally open up to nearly 10 degrees later this fall. That should be enough to allow telescopic observers to see divisions in the rings once again. When they’re edgewise, the rings look like a thick white line, and no divisions and individual rings can be resolved.

Saturn’s axis is tilted like Earth’s but a bit more at 27 degrees. Over the course of one Saturnian year (29.5 Earth years), we watch the north face of the rings slowly open to their maximum tilt of 27 degrees, followed by a return to edgewise over a period of nearly 15 years. Over the next 15 years, the south face of the rings tips into view up to a maximum of 27 degrees before returning back to edgewise. We currently see the north face.

This September photo by the Cassini probe looks toward the night side of Saturn, where sunlight reflected off the rings has dimly illuminated what would otherwise be the dark side of the planet. The planet casts a shadow that cuts across the rings in the top right of the image. A mind-bending perspective! Click on the photo to see a simulated wider view. Credit: NASA

Saturn has been lost in the solar glare since September, but now quietly returns to the morning sky in late October. Die-hards with great eastern horizons can go out 45 minutes before sunrise and look well below Leo the Lion (five fists below and left of Regulus) to spot the planet. Bring binoculars to help you scan the twilight glow for a single bright “star” – that will be Saturn. If you don’t see it now, just wait a little. In two to three weeks, Saturn will be higher at dawn and much easier to see.

The planet is near the autumnal equinox point located in Virgo and opposite Jupiter, which sits near the spring equinox point in Pisces. The two planets just happen to be in completely different parts of the sky. When Saturn rises, Jupiter sets. You might recall that the sun passes through the equinox points on the first days of fall and spring respectively.

Comet Hartley 2's moves through Auriga and Gemini for the remainder of the month. Each tick mark represents a day, and positions are plotted for 4 a.m. Central time (a couple hours either side won't make a noticeable difference.)Â The view shows the sky as you look due south and nearly overheard around 4 a.m. Created with Chris Marriott's SkyMap

Comet Hartley 2 makes its closest approach of 11 million miles to Earth Wednesday. We see it projected against the stars of Auriga the Charioteer from our homes on this rolling, revolving observatory we call Earth. As described in yesterday’s blog, the best viewing times are now well after midnight, in part because the comet’s low in the east during the evening, but also because of glare from the waxing gibbous moon. There have been many naked eye sightings of Hartley 2, but they’re from dark sky sites with the comet high in the sky at the time of observation. You should be able to spot it fairly easily now from the outer suburbs and countryside with binoculars after moonset.

The sun’s Southern Cross

Comet Hartley 2 passed the open star cluster NGC 1528 in Perseus last night. This 2-minute exposure made with a 200mm telephoto lens clearly resolves the cluster into individual stars. Photo: Bob King

I was surprised to see two “comets” when I pointed my binoculars at Comet Hartley 2 last night. The swift-moving Hartley had a fuzzy companion to its left which I knew must be a star cluster. A quick check in the atlas showed that it was NGC 1528, a cluster of stars in Perseus similar in size and brightness to the comet. Through 8×40 binoculars I couldn’t resolve any stars within the hazy puff at first – that’s why it looked so similar to Hartley 2. I concentrated my vision on a second try and discerned a few tiny twinklings and a granulated appearance common in many clusters viewed through binoculars. The telescope resolved NGC 1528 into lovely arcs of individual stars. I’m always grateful for the wandering ways of comets. As they travel across the sky, they often pass interesting objects I might not otherwise think to view. Tonight the comet will lie about one degree east of another star cluster, NGC 1545. I encourage telescope owners to use the comet to find its starry neighbor. Here’s a detailed map to help get you there.

The sun photographed by the space-based Solar Dynamics Observatory at 9 a.m. today. Each sunspot group has its official number. A large new spot is coming around the east side of the sun, while my boxy "Southern Cross" group is - appropriately - in the sun's southern hemisphere. Credit: SDO/NASA

I got another surprise this morning when checking recent pictures of the sun. Not only is there an exciting new spot coming into view,  but I was struck by the current sunspot group 1112, which is shaped almost exactly like the constellation Crux, better known as the Southern Cross. Of course, it’s only a coincidence, but the resemblance is striking. Since the sun’s bubbly, boiling surface is in constant motion, it’s likely the group will change shape by tomorrow. If you have a telescope equipped with a SAFE solar filter, you might want to check it out today.

Crux and sunspot group 1112 side by side. Crux image: Stellarium; sunspot: SDO/NASA

The Southern Cross is the smallest constellation in the sky, but because it contains two bright first magnitude stars and sports a distinctive and compact shape, it’s known the world over. You’ll find its image on the flags of Australia, New Zealand, Brazil, Samoa, Papua New Guinea and now – briefly – on the sun. The ancient peoples of Greece and Italy knew Crux, but the slow wobble of the Earth’s axis – called precession – has moved the constellation out of view for Europeans and most of the U.S. You can see the Southern Cross from Hawaii without difficulty, but it just clears the horizon for southern Florida during the spring months. Folks living in the southern hemisphere use Crux to point to the southern pole star, Sigma Octantis, the same way northerners use the “pointer” stars in the end of the Bowl of the Big Dipper to point to the North Star. They imagine a line through the top and bottom stars of the cross and extend it southward until it intersects with Sigma.

As long as we’re on a sunny topic, there’s a chance for aurora again tonight for high latitudes. A stream of subatomic particles from a prominence ejection on October 11 is behind the current activity, so if it’s clear where you live, take a look in the north for a telltale green arc.

Green comet, green aurora – astronomy’s going green!

Delicate rays and a bright green arc cut through the Bowl of the Big Dipper early this morning around 12:30. The green color is given off by excited oxygen atoms. The pink, invisible to the eye, is likely also oxygen, which can emit both red and green light when bombarded by subatomic particles from the solar wind. Photo: Bob King

I love it when a forecast proves true. That was the case last night when northern lights were predicted for high latitudes. While Duluth may seem like the Arctic, at 46.7 degrees north, we’re fewer than five degrees of latitude north of Chicago.  Not exactly high latitude but enough to make a difference.

A double auroral ray reaches upward from the arc. Photo: Bob King

I noticed the aurora around 10 o’clock as a glowing presence in the northern sky below the Bowl of the Big Dipper. Nothing obvious … at first. About the time I was ready to go to bed, I made the mistake of checking one more time to see if anything new had developed. Uh-oh, that subtle glow had strengthened into a bright green arc. Bye-bye sleep. I dug out camera and tripod and scouted the neighborhood for a spot with a good view to the north.

After midnight things took a new twist.  Faint spears of light materialized out of nowhere and weird, glowing patches probed the sky above the bright arc. It was fascinating to watch how the arc would intensify in one section and fade in another. All of this happened in the bottom 10 degrees of sky (one outstretched fist). Sky watchers at those higher latitudes – where the aurora was high above the horizon – must have seen a truly great show. Check out this photo taken the same night from Norway by photographer Ole Christian Salomonsen.

The space weather forecast calls for more activity tonight, so it might be worth your while to check the north before you turn in.

The green puff of Comet Hartley 2 wasn't far from Perseus' brightest star Mirfak (above right of center) in this photo taken last night. Details: 135mm lens at f/2.8, ISO 800 and 2-minute exposure on a tracking mount. Photo: Bob King

The moon is now returning to the evening sky, which means Comet Hartley 2 will soon become more difficult to see in the lunar glow especially in binoculars. The coming few nights you’ll still have good opportunities, but once the moon is 3/4 full, you’d do better to go out and view the comet in the morning sky after moonset. Reports indicate that sky watchers living near bright cities aren’t having much luck finding Hartley 2. Part of the reason for this is because the comet is very diffuse and susceptible to light pollution. The outer suburbs and the countryside are another matter. While you wouldn’t call it bright, Hartley 2 is easy to see in binoculars night after night as it wends its way across northern Perseus. Use the map below to help you find it. Click HERE for a more detailed sky chart.

The W or "zigzag" of Cassiopeia will still your guide to Comet Hartley 2 this coming week. Mirfak in Perseus is about two horizontally-held outstretched fists below the lower end of the W. Use binoculars to see the comet best. Illustration created with Chris Mariott's SkyMap software

There’s nothing like a spring morning on Vesta

Astronomers combined 146 exposures taken by NASA’s Hubble Space
Telescope to make this 73-frame movie of the asteroid Vesta’s
rotation. Vesta completes a rotation every 5.34 hours. Credit: NASA / ESA

Just 280 days to go. That’s when the Dawn probe will enter orbit around Vesta, the second largest asteroid in the main asteroid belt. In the meantime, the Hubble Space Telescope has been pressed into service taking hundreds of closeup photos of 329-diameter asteroid to help refine what we know about its spin and axial tilt. When the probe arrives next July, it will examine and photograph Vesta’s surface from an orbit that circles around the poles. Instruments on board include infrared and visible light cameras, spectrometers to determine what minerals make up Vesta’s crust, and a device that indirectly probes the asteroid’s interior by measuring its gravity field. Scientists are interested in asteroids because they were the original building blocks of the planets. The more we can learn about them, the better we’ll understand Earth’s origin and early history.

Vesta's about 220 million miles from the sun. That distance, combined with its small size, means that the Hubble Space Telescope can only distinguish the largest features on asteroid's surface. The dark areas are probably basaltic crust, the pink is surface dust and soil. Credit: NASA/ESA

After studying hundreds of new Hubble images, astronomers discovered that Vesta’s poles are tipped four degrees more to the asteroid’s east than expected. Since seasons are determined by the tilt of a planet’s or asteroid’s axis, the added tip means that the difference in seasons between the northern and southern hemispheres will lag about a month behind original predictions. Christopher Russell, Dawn’s principal investigator, explains:  “Because our goal is to take pictures of the entire surface and measure the elevation of features over most of the surface to an accuracy of about 33 feet, or the height of a three-story building, we need to pay close attention to the solar illumination. It looks as if Vesta is going to have a late northern spring next year, or at least later than we planned.” You’ll recall that it’s the tip of a planet’s axis that determines the height of the sun in the sky and the length of its seasons.

Comet Hartley 2 and the Double Cluster last night from Austria. Credit: Michael Jaeger

Friday and Saturday nights, Comet Hartley 2 scooted by the Double Cluster in Perseus. We ran a photo of that yesterday, but overnight, I received one of the finest pictures I’ve seen of the event. It was taken by the noted Austrian comet observer and photographer Michael Jaeger. This guy’s work is astoundingly good. Click on the image to see the mouth-watering version.

This map shows the sky as you face south around 2:30 p.m. today. Look for the thin lunar crescent with either your naked eye or, better, with binoculars. Once you've found the moon, the crescent Venus will be a short distance below and to its right. The pair is about 20 degrees or two outstretched fists above the horizon at the time for the northern states, but higher up for the southern U.S. Created with Stellarium

Venus photographed with a point and shoot camera through a small telescope at 2 p.m. today. North is up. Photo: Bob King

Some of you who’ve tried to find Venus in daylight and been frustrated may want to try again with the help of the crescent moon this afternoon. While the moon will be thin,  it might be easier to see than a point of light in the blue. Venus will be about 2 degrees below and right of the moon when the pair is due south around 2:30 p.m. your local time.  Haze-free, deep blue skies are best for making this observation.

I wanted to point out an error, since corrected, of the position of Mira on yesterday’s map of the constellation Cetus. I accidentally confused it with a star close to the same position. My apologies. Let us know how your whale hunt goes!