Monthly Archives: October 2010

The scary side of night

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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

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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.

Orion shows his cards, and an asteroid whizzes by Earth

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Orion and his famous "three in a row" Belt stars clear the trees around 11 p.m. last night. Photo: Bob King

A big storm blew in this week and left a few inches of snow at my place. Almost all of it’s gone now, but when I drove north of town to take in the starry sky last night, I opened the car door and stepped into four inches of the crusty white stuff. When the first snow arrives and stays around, your whole perspective changes. At least for me, I think winter. The Summer Triangle and early autumn constellations of Capricornus and Aquarius seemed strangely out of place. Looking up last night I thought “what are those guys still doing here?”

Things fell into place when Taurus and then Orion rose. They were a better match for the landscape and my new mindset. I especially enjoyed watching the three Belt stars rise due east in a nearly vertical line.  Orion’s bright, twinkling stars help me accept winter’s coming cold and darkness with anticipation.

2003 UV11 will be in western Pegasus near the star 1 Pegasi tonight during convenient viewing hours for the Americas and Canada. You'll need a telescope to see it. Created with Stellarium

A little asteroid named 2003 UV11, measuring only about 0.4 miles (600 meters) across, started its race across last night’s sky. I trained my telescope on the star-like point of light and watched its slow glide through eastern Pegasus for 15 minutes.  At the time it was 1.9 million miles from Earth, close enough to see it move in real time at medium magnification. What was most fascinating – at least to me – was that it chugged along in response to the sun’s gravity. You usually don’t get to see a solar system body move so quickly. When you do, you get a sense of the sun’s invisible power, the same power that tugs and illuminates Earth and asteroid alike.

There are tons of asteroids in the sky, but only a small number like 2003 UV11, that are both bright enough to see in modest telescopes and close enough to detect movement in just seconds of time. Things got interesting when the asteroid tracked very close to a bright star. You could clearly see it creep past the star second-by-second and then move on to the next. Since 2003 UV11 is 12th magnitude, it’s within range of 4-inch telescopes (from a dark sky) and larger scopes under more light-polluted locations.

The orbit of asteroid 2003 UV11 takes it very near Earth tonight. The diagram shows the layout of the inner solar system planets and the asteroid today. Credit: NASA/JPL

Tonight the asteroid makes its closest approach to our planet around 11 p.m. Central time when it will be 1.2 million miles away. Advanced amateurs can watch it buzz through western Pegasus near Delphinus the Dolphin at nearly double last night’s pace. It will still be about 12th magnitude but gradually fading through the night. By tomorrow, 2003 UV11 will be considerably farther away and much fainter. You’ll need a large amateur telescope to see it at all. That means tonight’s the night!

While you can hand-plot the asteroid’s positions on a detailed star chart, your best bet is to use a planetarium-style software program like CyberSky or SkyMap and input 2003 UV11′s orbital elements into the program’s asteroid catalog. Then you can create your own map showing its position every hour or half-hour or whatever time interval you like.

The rubbly asteroid Itokawa is 540 meters across, nearly the same size as 2003 UV11. The photo was taken by the Japanese Hayabusa space probe. Credit: JAXA

You’ll find an ephemeris and orbital elements HERE or you can go to JPL’s Horizons Web-Interface and generate your own ephemeris by selecting your city, the target body – 2003 UV11 – and time interval for viewing. After you’ve made your choices,  click the generate ephemeris button. Then you can either plot the positions on a star map or input the orbital elements shown into your program. Remember that all times listed at both links are Universal Time. Good luck in spotting this high-speed, flying mountain!

Allow me to introduce you to Venus’ dark side

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Although invisible to the eye, Venus - along with Mercury - show up nicely in the coronagraph of the orbiting Solar and Heliospheric Observatory this morning. The lines are electronic artifacts caused by the bright planets. Credit: NASA/SOHO

What should you care that Venus is in inferior conjunction with the sun tomorrow? I mean, you can’t see the planet with the naked eye – it’s too close to the sun in the daytime sky. But there’s at least one reason why this conjunction brings good news for Venus watchers. It’s a sign the planet will soon return for a fine appearance in the morning sky. If we’re patient, we’ll be face to face with the goddess of beauty again in just a couple weeks.

As Venus orbits the sun, we see it pass through phases just like the moon. They're caused by the changing angle the planet makes with respect to the sun and Earth during a Venusian year. As seen by an observer (orange figure), Venus' phase wanes from half to crescent (left side) until reaching inferior conjunction (center). After tomorrow, the planet will move off to the right and appear as a thin crescent in the morning sky. Illustration: Bob King

While it may sound politically incorrect, inferior conjunction simply means that Venus is exactly between the Earth and the sun. As we gaze it its direction, we see the planet very close to the sun in the sky, because it’s in the same line of sight.

Venus' orbit is tilted about 3.5 degrees in relation to the Earth's, causing it to swing north of south of the sun during most conjunctions. Credit: Theresa Knott

You might think that Venus would cross directly over the sun’s face during conjunction, but its tilted orbit typically causes it to pass several degrees north or south of our star. That’s the case this time when the planet will lie only 6-7 degrees (about three fingers held together at arm’s length against the sky) due south of the sun today and tomorrow. Only experienced amateur astronomers exercising great care with the proper solar filters might attempt to tackle the task of spotting the planet. Should they succeed, the view would be unforgettable. Because Venus’ unlit backside is presented toward us, only an ultra-thin rind of crescent along its topside will be visible. While exceedingly delicate, the crescent will appear its largest since March 2009, with a diameter of one minute of arc or 1/30 the size of the lunar crescent. That’s theoretically big enough to resolve its shape with the naked eye. Too bad the searing sun will make Venus unviewable!

The thinnest edge of Venus will catch a bit of grazing sunlight today and tomorrow. Only 1/20 of 1% of the planet facing Earth is illuminated by sunlit during this inferior conjunction.

Venus’ large size is due to its proximity to Earth. Venus gets closer to us than any other planet around the time of inferior conjunction – today it’s just 25 million miles away. Even Mars, the solar system’s publicity hound, can only pull within 34.6 million miles of Earth at best. Since Venus is closest to us, it also moves fastest. During the upcoming two weeks, it will swing to the right of the sun – as seen in the diagram above – and pop out into the morning sky for easy viewing.  We’ll start to notice its return in mid-November, when the planet will still be a very thin crescent. Maybe you’d like to see how sharp your vision is and try to see its shape. I’ve tried but never accomplished this feat of eyesight. Instead I use binoculars. Through them, the Venusian crescent stands out crisply – a wonderful sight.

Venus looks like a perfectly black, circular sunspot when it transits the sun as it did in June 8, 2004.

On rare occasions, Venus passes directly in front of the sun at inferior conjunction. They’re called transits, and they come in pairs separated by eight years that occur every 122 and 106 years. The last one took place on June 8, 2004 and the next will occur on June 6, 2012. The previous pair was in December 1874 and December 1882. My daughter Maria and I drove two hours through a thunderstorm in 2004 to catch the transit just after sunrise outside the city of Tower in northern Minnesota. She remembers the trip well, because we had to turn around as soon as Venus exited the sun’s face, so she could get back to Duluth in time for school. I love astronomical adventures.

Through November and into winter, Venus will pull away from the sun and shine brilliantly at dawn. It remains in the morning sky until August of 2011, when it reaches superior conjunction and once again appears too close to the sun to observe. In astronomy, superior  means ‘outside’ or ‘beyond’ as opposed to inferior which means ‘below’ or ‘nearby’. During a superior conjunction with the sun, Venus will on the opposite side of its orbit from Earth (top position in the diagram) and farthest from our planet.

Will Comet Hartley 2 spawn a new meteor shower?

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Comet Hartley sports a short tail extending to the lower right in this photo taken earlier this month. Credit: Michael Jaeger

It’s very unlikely, but two intriguing pieces of evidence point to Hartley 2, the comet of the moment,  as a possible source of two recent bright fireballs seen over Canada and the southeastern U.S. On Oct. 16, two NASA all-sky cameras photographed a bright, slow fireball over Alabama and Georgia. What was odd was that this fireball was very similar to one photographed five hours earlier by the all-sky cameras network of the University of Western Ontario. Because the fireballs were seen by multiple cameras – each with their own perspective on the events – they were able to triangulate the fireballs’ positions and determine where in space they originated.

Guess what? “The orbits of the two fireballs were very similar,” according to Bill Cooke of NASA’s Meteoroid Environment Office. “It’s as if they came from a common parent.” The orbits of the two fireballs were not only similar to one another, but also roughly similar to the orbit of the comet. Since comets spew dust and small chocolate-chip sized gravel as they go, and since Hartley is close enough to Earth right now for our planet to potentially graze its dust trail, the fireballs could have originated there.

Two fireballs with "Hartley-esque" orbits observed on Oct. 16th by cameras in western Ontario (left) and the southeastern USA (right). Orbits of each are shown at top. Credit: UWO/NASA/Bill Cooke

It also could be pure coincidence. Cooke points out that on any given night at least a few Hartley-esque meteors hit the atmosphere. But you never know. If more meteors are on their way from Hartley, we ought to find out soon. A possible shower of Hartley dust might occur on the nights of November 2 and 3. If it happens, they’ll appear to emanate from the constellation Cygnus, which is nearly overhead when night begins. Since meteor showers are named after the constellation from which they originate, this one would be called the Cygnids. Will they show? Probably not but who knows. I plan to be out there just in case, and you might want to, too.  Click HERE for more information.

I wanted to share two excellent photos of the full or nearly full moon submitted by readers this past week. Thank you Jane and Andrew! Very nice work guys. Enjoy.

The full moon rises along with the Earth's shadow at Brighton Beach in Duluth last weekend. Credit: Jane Gilley

 I like how the sunlit peaks guide your eye to the moon in this photo taken in the Sierra Nevadas. Credit: Andrew Kirk

Space station sidesteps space junk this morning

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NASA astronaut Shannon Walker, Expedition 25 flight engineer, is pictured last week with a bag of M&Ms floating in air. Check out the sign behind her - that's the speed of the station in orbit. Credit: NASA

This morning at 5:25 a.m., while most of us were sleeping, astronauts aboard the International Space Station (ISS) fired the thrusters on the docked Progress cargo ship to steer the station from a possible collision with a piece of the now-defunct Upper Atmosphere Research Satellite (UARS). The tracking data indicated that the debris would have passed 1.2 miles from the station in overall miss distance, but less than half a mile within the three-dimensional “box” used for evaluating potential hits.

From September 21-30, 2006 the average area of the ozone hole was the largest ever observed, at 10.6 million square miles. The blue and purple colors are where there's the least ozone; the greens, yellows, and reds are where there's more. Credit: NASA

UARS was originally launched by the shuttle Discovery back in 1991. It operated for 14 years before it was decommissioned in 2005. The probe’s main mission was the study of Earth’s atmosphere, with particular emphasis on the ozone layer. Data from the orbiting observatory proved conclusively that human-made chlorine from refrigerants depletes ozone and is responsible for creating the large hole in the ozone layer above Antarctica. Ozone blocks dangerous ultraviolet light from the sun from reaching the ground. We never want to lose the ozone layer, because excess UV light is harmful to plants, disrupts the marine (plankton) food chain, and can cause severe sunburns, eye problems and cancer. Nothing good.

Now that the morning’s excitement is over, you can catch a view of the space station this week from your home. It’s back for easy viewing during early evening hours from now through the first half of November. I’ve listed Central Daylight times below for passes visible in the Duluth, Minnesota region. For times for your town, click HERE and type in your zip code or login to Heavens Above.

* Tonight beginning 8:27 p.m. and visible for less than half a minute very low in the southwest. Only for hard-cores.
* Wednesday at 7:19 p.m. low across the south. The ISS will be become almost as bright as Jupiter.
* Thursday at 7:45 p.m. This one will be interesting.  The station will rise in the southwest, and just as it reaches greatest brightness and highest elevation, will quickly fade from view. The reason? It enters Earth’s shadow. Watch the craft change color from yellow-white to deep orange through binoculars as it experiences sunset some 220 miles overhead.
* Friday at 6:37 p.m. during bright twilight across the south and southeast. A second, brief pass happens at 8:11 p.m. low in the west. The ISS will appear for only a minute or so before entering Earth’s shadow.
* Saturday at 7:02 p.m. An excellent, high pass high in the sky that cuts through the middle of the Summer Triangle.
* Sunday at 7:29 p.m. While you’re out trick-or-treating, watch for this nice pass high in the northern sky.
* Monday at 6:20 p.m. Although twilight will be bright, the space station will be bright enough to be visible before any stars are out. Its magnitude rises to -3.6 as it passes nearly overhead.

Goodbye, white pine

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My white pine joins a spectacular aurora in November 2004. Photos: Bob King

More than a year ago, one of my favorite “scenic” trees, a 60-year-old white pine that once spread its feathery branches over our driveway, was struck by lightning. Weakened by the blow, the tree’s time was up. We hired a fellow to cut it down and chainsaw its trunk into chunky lengths. I hated to see the tree go. One of the best sounds in the world is wind through pine boughs. It was beautifully shaped – a classic whirled form – and I loved including its lively outline against the night sky in my astrophotos. An interesting foreground is a key element in any good photo of the night sky. This pine had always been up to the challenge.

After cutting, the tree was transformed into a series of squat wood cylinders each about a foot and a half high. I piled these into a neat stack where they sat drying in the sun for months.  At the end of last summer, I moved them by wheelbarrow to the backyard fire pit, where they dried out some more.

This past Friday night was perfect for a bonfire. Cool but not cold, a light breeze from the north. Under a brilliant full moon, I decided it was time to put new life into my old tree. When the blaze was full and hot, I rolled the first of several of its hefty rounds into the flames. Then I sat back and enjoyed a satisfying show of light, heat and flames. Before returning to the fundamentals of energy and ash, my white pine was giving back one more time. Once a pretty foreground object, it was now the center of my attentions.

The International Space Station cuts across the sky after rising from behind my favorite pine in a photo taken two years ago.

While tossing on another length and enjoying the huge shower of sparks that took off for the heavens, it occurred to me to take one last portrait of the tree in celestial company. I propped up the camera on the ground and made a few images before settling back onto the bench to soak in more warmth.

Sparks from the burning white pine rise toward the full moon Friday night. Photo: Bob King

I stayed up by that fire until after 1, not wanting to go to bed. Happily, my pine has several additional lives remaining, since there’s much wood left to burn. I counted 11 big rounds,  easily enough for a week’s worth of nights. I don’t think I’ll mind this lingering goodbye before the tree departs for good – except in the images you see here.

Do-it-yourself aurora forecasting

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Shimmering curtains of aurora hang over a snowy landscape just outside of TromsØ, Norway on October 11. Details: Canon 5D Mark II, 24 mm lens @ f/1.4 / ISO2000. Credit: Ole Christian Salomonsen

Today’s space weather forecast from the NOAA/Space Weather Prediction Center predicts a fair chance for major auroral storms at arctic latitudes and minor storming for mid-northern latitudes tonight and tomorrow night. Minor storms for both regions are again possible on Tuesday. All this aurora potential has me thinking that it’s time to pass along two key ways to find out if the aurora is busting out at your location. All you need is a computer or phone with Internet access.

The northern auroral oval pictured this morning at 9:41 a.m. using date from the POES satellite. Red indicates strong auroral activity. Credit:NOAA/SWPC

We’ve touched on one of the methods in earlier blogs. You go over to the NOAA POES Auroral Activity site and check the extent of the auroral ovals, those caps of glowing auroral light centered on the Earth’s north and south geomagnetic poles. If you see the orange-red edge of the oval close to, touching or spilling right over your location, it’s time to put on a coat, run outside and survey the northern sky for possible northern lights. NOAA constantly updates the oval’s size and intensity based on data received from the Polar Orbiting Environmental Satellite (POES). A second, more precise way to determine if aurora’s likely in your neighborhood is to check the estimated 3-hour Kp index. OK, I know it sounds pretty geeky, but the index is very easy to use. Kp is a number that measures the likelihood of witnessing an aurora, and it’s determined by a grid of nine magnetometers set up around North America. Magnetometers measure the strength and direction of magnetic fields just like the ones we’re familiar with from playing with magnets. The aurora produces changes in the Earth’s magnetic field that are picked up by these magnetometers, which are relayed to NOAA and used to forecast current and upcoming activity.

The map above shows what the minimum value of the Kp index needs to be to at your location in order to possibly witness the aurora. A value of 3-4 suggests the Upper Midwest might see an aurora. Remember that factors such as moonlight, city light pollution, and cloud cover will affect the visibility of any auroral activity. Credit: NOAA

Take a look at the map at left. For Duluth, Minn., the Kp only has to reach 3-4 for the possibility of aurora. The further south you go, the higher the index has to be for aurora to be likely. The K- index is plotted as a series of 3-hour-wide bars ranging in height from 0 to 9. They’re also color-coded, with green representing a low Kp, or little chance for aurora, up to my favorite color red, which begins at level 5 and extends to the maximum level of 9. If you live in Chicago, the index has to rise to 5-6 for the possibility of aurora; for the Carolinas and Florida a maxed out 9 is necessary.

Although it can get cold in Minnesota, one of the advantages to living here is our lower Kp index threshold. Hmmm … something to advertise in those tourist brochures.

This is the Kp index plot made at noon today. Each bar represents a 3-hour interval. You can see a spike in activity yesterday morning the 23rd. Credit: NOAA/SWPC

When you use the index, be aware that the dates shown begin at 0 hours UT (Universal Time) or midnight if you live in London, England along the world’s prime meridian. Those are the dotted lines in the plot at right. To convert to Eastern Daylight Time, subtract 4 hours; Central time, subtract 5 hours, Mountain time, -6 and so on.

I’d love to hear how well the Kp plots work for observers, and whether you’re able to forecast an aurora right from your home computer. As we approach the next sunspot maximum, predicted for July 2013, check the Kp index against your sightings of aurora and let us know how closely they match.

Scientists discover lunar oasis; shady events on Jupiter tonight

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The Centaur rocket stage separates from the LCROSS craft on its way to impact with the moon last year. Credit: NASA

Before we wrap up our appreciation of the full moon, can I add one more way? Last October 9, the LCROSS spacecraft and its companion rocket stage were crashed into the floor of the lunar crater Cabeus near the moon’s south pole. Earlier, scientists had picked up hints of water ice in this and other craters in the polar regions. The lunar poles are literally areas “where the sun don’t shine.” They likely acquired their ice from long-ago comet hits, and it’s been preserved in the shadows ever since. Steady temperatures of 280 below zero Fahrenheit are common in a number of polar craters – low enough to prevent water ice from vaporizing for at least a billion years.

By observing the resulting impact plume, scientists initially confirmed the presence of water ice. Fast forward to this week when NASA scientists announced that much more ice and vapor were seen in the plume than expected. How about 41 gallons?

A temperature map of moon's south pole. The blues and purples indicate craters and areas that are -280 degrees or lower -- perfect spots where water ice or other icy compounds seen in comets could be trapped in a deep freeze. Credit: NASA

Mission chief scientist Anthony Colaprete of the NASA Ames Research Center calculates there could be 1 billion gallons of water in Cabeus. Talk about an oasis in a lunar desert! The water is in the form of ice grains bound up with the lunar soil, but could be separated and used by future astronauts as drinking water. That’s not all that LCROSS kicked up. Scientists found methane, ammonia, hydrogen gas, carbon dioxide and carbon monoxide as well as relatively large amounts of light metals such as sodium, mercury and possibly even silver. That nasty ammonia and methane can be processed to make rocket fuel. All of these compounds and ices in the lunar soil indicate that the moon has a “water cycle” of sorts, where icy vapors from comet strikes in the distant past may have migrated to the poles where they condensed into ice and interacted with other compounds. “The diversity and abundance of volatiles in the plume suggest a variety of sources, like comets and asteroids, and an active water cycle within the lunar shadows,” says Colaprete. Direct your gaze to the southern edge of the moon tonight and think about the unexpected treasures there. You’ll find more information HERE and some cool videos HERE.

Bright Capella, low in the northeastern sky, and the moon can help you find Algol. Around 7:30 p.m. Central time, the star will be nearly as bright as nearby Mirfak. By 11, Algol will more closely resemble Rho. Created with Stellarium

Although it looks like clouds for northern Minnesota this evening, if the weather’s fair by you, there are two interesting things going on tonight – one visible with the naked eye, the other in small telescopes. The Demon Star Algol in Perseus will undergo an eclipse by its larger, fainter companion. Mid-eclipse, when Algol is faintest, occurs at 11:10 p.m. Central time. This is ideal for watching Algol fade from near maximum brightness to minimum. If you’re out early, use the moon to help point you there. From nightfall until about 8:30 p.m. the star will appear its normal brightness. Look again around 10:30-11 p.m. and you’ll see it’s dimmed noticeably. For more information on Algol and its eclipses, check out this previous blog on the topic.

When shadows cast by Jupiter's moons move across the planet's face, they're called shadow transits. Catch the Europa-Ganymede "double feature" tonight between 8:40 and 10:04 CDT. The map shows the view in a typical telescope with south up. Created with Chris Marriott's SkyMap

I’m going to hate to miss this next one – a simultaneous shadow transit of the moons Europa and Ganymede across the face of Jupiter. Between 8:40 and 10:04 p.m. Central time, the shadows cast by the two moons will appear as inky black dots on Jupiter’s cloud tops. If you could somehow float in a balloon within the shadow, you’d see an eclipse of the sun.

Europa’s shadow is a little larger than a pinpoint, while Ganymede, the largest of the Jupiter’s moons,  looks more like a small dot. I’ve drawn the map for around 9:15 p.m when they’ll both be most easily visible at the same time. Ganymede itself is well removed to the left of Jupiter; Europa is in front of the planet until about 9:40, when it begins to move off and to the side of the planet. If you use high power, you can watch Europa – a tiny white speck – glide off the disk in real time. A wonderful sight!

10 ways to enjoy tonight’s full moon

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The moon’s done it again. Ambled its way along the ecliptic to another full moon phase. Appropriately enough, this month’s full moon is called the Hunter’s Moon. It rises in the northeast in Aries the Ram and stands high in the south around midnight. While you’re out this evening, I’ve prepared a list of 10 things to see or reflect upon while you and the moon are beaming at one another.

Earth's atmosphere takes away the moon's blues, leaving it orange. Photo: Bob King

1. Dramatic colors – Moonrise for Duluth is 5:35 p.m. or about 35 minutes before sunset. If you can get to location with an open view to the east, try to catch the moon just as it’s clearing the horizon. Depending on the state of the atmosphere, the moon will rise in technicolor red or orange. Longer wavelength red light penetrates air and dust, while blues and greens are scattered or absorbed. Once the moon is a fist or so above the densest layer of air, it assumes its usual white color. You’ll recall that white light is a mix of all the colors of the rainbow spectrum. In the thinner air high above the horizon, all the colors – except a bit of the blue – make it through to give us back a pale moon.

The moon is very out-of-round (right) when rising compared to when it's higher up. Atmospheric refraction is the cause. Credit: Jim Schaff

2. Distorted shape – The atmosphere also acts like a lens and bends or refracts the moon’s light. There’s no time better to see this than during a full moon rise, when the moon’s lower half is closer to the horizon than the upper. Thicker air at the horizon “pushes” the lower half of the moon upward into the less-heavily refracted top half, causing the moon to appear flattened or squished. If you’re ever lucky enough to see the moon directly on the horizon, you’re only seeing an optical illusion. Refraction there is strong enough to lift the moon into view even before it’s truly risen!

The dusky band beneath the rising moon is the Earth's shadow. Photo: Bob King

3. Earth’s shadow – The moon rises along with Earth’s shadow tonight. You won’t see the shadow at first, because the sun won’t have set yet, but beginning at sunset and continuing for the next 20 minutes, you’ll notice a thick, blue-gray band in the east beneath the moon.  That’s our planet’s shadow. It extends all the way around the eastern horizon, and rises until it gradually merges with the darkening sky.

4. Eminently quotable – You’ll find many mentions of the moon, particularly the full moon, in literature, TV and other media. Here’s a sampling:

“Promises are like the full moon, if they are not kept at once, they diminish day by day.” – German proverb

“Moonlight is sculpture; sunlight is painting.” – Nathaniel Hawthorne

” Everyone is a moon, and has a dark side which he never shows to anybody.” – Mark Twain

Can you see the moon rabbit or the lady in the moon? Tonight's the night.

5. Make a face – You can see almost anything you want in the face of the moon. The dark spots, called lunar seas, contrast with the white regions known as the lunar highlands, creating patterns that give us everything from the familiar “man in the moon” to the lady of the moon, the alligator of the moon and anything else your imagination can conceive. As you making faces up there, consider that the lunar seas are impact holes that later filled with lava from below, while the white areas are ancient crust carpeted with craters from asteroid and meteorite bombardment in the early days of the moon’s formation.

Craters are labeled in white in this annotated photo of the full moon

6. Binocular exploration – Bring your binoculars tonight and see how many lunar seas and craters you can spot. The seas are obvious, while the four most prominent craters labeled at right require only a little extra effort.  Huge systems of bright rays surround each crater and make them easy to spot. The rays originated when boulders sent aloft from the crater impacts rained back down, striking the moon and creating thousands of mini-craters, each of which excavated fresh soil from the moon’s surface.

In this full moon photo, you can see the terminator scraping along the top or north edge of the moon. Nice shadow detail shows up in the craters on the moon's north edge, because the terminator there is the day-night border where shadows are long. Credit: NASA

7. Terminator madness – At full moon, the sun, Earth and moon are lined up in that order, and the sun shines squarely on the moon’s face, lighting it up completely. During other phases, we see only part of the moon; the terminator, or day-night line, separates the lit part of the moon from the unlit. At full moon, the terminator essentially disappears because the entire face of the moon is in sunlight. Truth be told, it doesn’t disappear completely. The lineup that I mentioned earlier is exact only in the case of a total lunar eclipse. The moon’s orbit is slightly inclined with respect to Earth’s orbit, so it’s usually a little north or south of the sun-Earth line. Tonight it’s far enough north of that line that telescopic observers will see the terminator running along the south edge of the disk below the prominent crater Tycho. To the naked eye, the moon will appear perfectly circular with no nibbling about the edges. By tomorrow, the terminator will have swung around to its usual post-full moon position on the west side of the disk. To see the “southern terminator” to best effect, look between 7-10 p.m. Central time. The exact moment of full moon is 8:36 p.m. CDT tonight.

The moon's black disk covers the sun during a total solar eclipse. In the distant future, this will be a thing of the past. Credit: Luc Viatour

8. Slip slidin’ away -The difference in the moon’s gravitational pull on the nearside versus the farside of Earth causes the two tidal bulges. Coastal residents are familiar with as the ocean tides. Some of the energy from this moon-Earth interaction causes our planet’s spin to gradually slow down. The spin energy is not wasted, but transferred out to the moon, causing it to move 1 1/2 inches farther from our planet each year. Over several billion years, the Earth’s spin will slow to eventually match the orbital period of the moon. On that far future day, we’ll be locked facing one another so only the inhabitants of the moon-facing side of the Earth will see the moon. Those living on the Earth’s “farside” will have to travel to the other hemisphere for a look-see at the moon. Weird to contemplate, but it’s inevitable. One other consequence of this tug of war is that a more distant moon will also appear smaller, and a smaller moon won’t be able to completely eclipse the sun. The days of the total solar eclipse will be over.

The Earth's tilted axis is stabilized by the moon's gravitational influence.

9. Thank you for being our friend – One of the wonderful things the moon does for our planet is keep its axial tilt stable. Without the moon, the Earth’s axis would wobble to more extreme tilts like Mars’ axis does, causing catastrophic climate changes. The moon stabilizes our axis and keep our planet’s alignment from going to extremes.

10. Moonlight on linen – After an evening with the full moon, leave the lights off for a few minutes when you return to your home or apartment. If you have an east or south-facing window, you’ll be treated to the sight of moonlight spilling on the floor, the bed and curtains. Though the moon only reflects 7% of the sunlight striking it, it seems strangely brilliant and alien. When I see that I’ve unwittingly allowed the moon into the house, it never fails to stoke my sense of wonder at how close the universe is.