Aurora borealis and food for the soul

The Aurora Borealis in Manitowish Waters, Wis. Photo: Bob King

Just returned from a visit to snowy northern Wisconsin where I ran across a new restaurant I’ll have to check out sometime. What astronomy enthusiast wouldn’t?  It’s called the Aurora Borealis and I bet they serve up more than protons and electrons. A quick look at the reviews shows high praise for the crab cakes. You can find it in the wee town of Manitowish Waters.

Aurora borealis near Tromso, Norway on the evening of Dec. 15, 2012. The ice was perfect for skating. Details: Canon 5D Mark III + Nikon 14-24 f/2.8. Click photo for large version. Credit: Ole Salomonsen

The real aurora’s been scare of late at mid-latitudes but not so in the Arctic. Ace aurora photographer Ole Salomonsen took this photo on Dec. 15 he called “Cracks on Ice” from near Tromso in northern Norway. With ice 16 inches thick conditions were perfect for skating. Sadly, Salomonsen didn’t bring a pair. Should I ever have the experience of skating while the aurora wriggled overhead, I promise to face my inevitable death with a happy face.

The sun photographed by NASA’s Solar Dynamics Explorer at 3:15 p.m. (CST) today. Credit: NASA

Auroras are closely linked to solar activity, which has been on the wimpy side the past month. At the moment there is only one developing sunspot region kicking out modest C-class flares – Region 1635.

Prospects look better on the solar farside, which has been throwing fits the past 48 hours, spitting out streams of high-speed protons and electrons in the form of coronal mass ejections.

A backside CME (coronal mass ejection) photographed by the Solar and Heliospheric Observatory around 7 a.m. (CST) this morning. The sun, shown as the white circle, is hidden from view by an occulting disk. Credit: NASA/ESA

While none of these are aimed toward Earth, these farside blasts could mean that sunspot activity there is picking up.

If we’re lucky, we’ll start seeing what appear to be several large, active sunspot regions as they rotate around to the nearside in the coming days.

Perhaps chances for northern lights will come along with them.

Let’s hope so. I’m sure you’ll agree that the aurora borealis is real good food (for the soul).

Ultraviolet photos taken by the STEREO behind and STEREO ahead solar observatories this afternoon which can see the backside of the sun. Many of the bright blobs you see are sunspot groups on the sun’s farside. Credit: NASA

Happy New Baktun and a joyous solstice to all

Circumscribed halo around last night’s half moon. Photo: Bob King

Today the Mayan calendar rolls over to a new Baktun or 144,000 day cycle as it has for centuries. Coincidentally, it’s also the first day of winter in the northern hemisphere and summer for folks down under. Winter tiptoed in at 5:12 a.m. (CST) this morning while many of us were snug in our beds. Looking out my window, the world looks much the same as it did yesterday – with a difference. It’s sunny!

Come join Duluth’s celebration of the solstice at the University of Minnesota-Duluth’s planetarium.

That means a clear sky tonight and a chance to celebrate the new season. If you live in the Duluth, Minn. region, the Marshall Alworth Planetarium will feature a special “End of the World – Winter Solstice” party with shows on the half-hour in the dome, telescope viewing, pizza, cider, a raffle and a free 2013 calendar. Cost is $8 per person or $15 per family. The event starts at 6 p.m. and runs until 9. More information HERE.

Only 8 hours and 32 minutes separate sunrise and sunset in Duluth, Minn. today. The rest belongs to the night. Solstice is combination of two Latin words – sol for sun and sistere to stand still. That’s what it feels like for a week or two at the time of the summer and winter solstices, when the sun reaches its highest and lowest points in the sky.

The seasons are caused by the 23.5 degree tilt of our axis. In summer, Earth’s north polar axis is tipped toward the sun, causing it to appear higher in the sky and making for longer days. Half an orbit later in winter, the north polar axis is tilted away from the sun, making for a low sun and short days. In spring and fall, the axis is tilted neither toward nor away and day and night are equal. Credit: Tau’olunga with additions by Bob King

On Dec. 21 the sun reaches its lowest altitude above the southern horizon at noon for the year. Here in Duluth, that’s about 20 degrees or two fists held at arm’s length. For Chicagoans, it’s 25 degrees, a bit higher. But if you live in Anchorage, the yellow orb of day climbs to just under 6 degrees before slinking back toward the west. My dear brother Mike who lives there must wait until 10:14 a.m. for the sun to rise today. With sunset at 3:42 p.m., he’ll need to be vigilant to catch sight of it. Buildings and trees could easily block the sun from view. .

Excellent, short video on how the seasons happen

These extremes of daylight and night are brought on by Earth’s tipped axis. If it ran straight up and down, much as Jupiter’s axis does, sunrise and sunset times would barely vary for your location. The sun would rise in the east and set in the west 12 hours later every day of the year. No variation and no seasons. Who wants that?

Thanks to the Earth’s tipped axis we experience the joys winter and the ice it brings. These are air bubbles trapped in pond ice near my home yesterday. Photo: Bob King

The tip ensures that the northern hemisphere of the planet tilts toward the sun in the summer and away in the winter. As a consequence, the sun appears very high in the sky in summer. Its longer, steeper path naturally means longer days and more intense heat. In the winter, we’re tipped away from the sun. Slanted, less intense solar rays and short days follow.

Vesta shown at 9:30 p.m. (CST) every 5 days now through Jan. 10, 2013 as it glides near the Hyades cluster. 97 Tauri is mag. 5.  Stars shown to 7.5 magnitude. Created with Chris Marriott’s SkyMap software

If you’re looking for an interesting astronomical treat in the night sky this solstice, face east anytime during the evening hours and find the brightest “star” you can see. That’s the planet Jupiter. Just below Jupiter is the bright star Aldebaran and a V-shaped pattern of stars called the Hyades star cluster. Not far from the cluster is the famous asteroid Vesta. You’ll recall it was was orbited and studied by NASA’s Dawn spacecraft this past year.

Vesta shines at magnitude 6.5 (just under the naked eye limit), as bright as it gets this year. The star-like asteroid is super easy to see right now in binoculars, especially with Jupiter to help point you there. Take a look the next clear night.

7 fun things to do while waiting for the world to end

Mayan 7-day weather forecast for the current week

First, brew a cup of tea or coffee, sit back at the computer and spend a few minutes at the website for edification and entertainment. The site’s creators have tried to address every cooked-up doomsday scenario out there.

Second, why not use the time to finish wrapping those Christmas presents? I usually wait till the last minute and do a schlock job folding and taping. Don’t let this happen to you. And if you’re looking for a last-minute gift, give your worried friend the hope of another tomorrow with a 2013 calendar.

Photo: Bob King

Third, take a really long walk or engage in some other form of exercise. Do this in advance of all the overeating that’s inevitable around Christmastime and you might break even.

Fourth, if you do plan a walk and your sky is clear, do so under the light of the quarter moon. Tonight it’s high in the south in the constellation Pisces and sure to provide good light for shadows. If it’s snowy where you live, the moonlight will be even more intense.

Orion’s Belt is filled with stellar riches. Photo: Bob King

Fifth, look at Orion’s Belt in a pair of binoculars. I know you’ve seen this stellar trio dozens of times, but the region surrounding them is saturated with stars just below the naked eye limit.

Point your binoculars that way for an awesome view before the moon gets too bright. Several nights ago under a very dark sky, I  could see the bling with my naked eye, palpitating at the limit of vision.

Comet C/2012 K5 (LINEAR) on Dec. 15 from Austria taken with an 8-inch scope. Smaller scopes will show a faint fuzzy streak, while 8-inch and larger instruments will give fine views of the tail. Detailed finder map below. Credit: Michael Jaeger

Sixth, if you own a telescope 6-inches or larger, a beautiful comet is passing atop the Bowl of the Big Dipper this week. Comet C/2012 K5 LINEAR shines at around 9th magnitude with a teeny-tiny head and a streamlined tail pointing northwest. I saw it in my scope the night of the Geminid shower. Absolutely beautiful. The larger your telescope, the better the view.

Seventh, call your mom or dad or someone in your family you haven’t talked to in a while and get back in touch.

Comet K5 LINEAR flies skirts the Big Dipper Bowl the next few nights. I’ve marked the comet’s position every 12 hours at 6 a.m. and 6 p.m. CST. The morning hours from 5-6 a.m. are best because the sky is moonless and comet high in the northern sky. Right-click image, save and print out a copy to use at the telescope. Stars to mag. 9.2. Created with Chris Marriott’s SkyMap software

Curiosity snoops around ‘Shaler’; Comet L4 PanSTARRS update

The Curiosity Rover used its high-resolution mast camera to photograph this rock outcrop called “Shaler” in the Glenelg area of Gale Crater on Dec. 7, 2012. The area in the photo spans about 3 feet in the foreground. Click to enlarge. Credit: NASA/JPL-Caltech/MSSS

Curiosity rover, clueless about the end of the world, is spending this week tooling around a shallow depression called Yellowknife Bay looking for a good rock to drill. The images it’s been returning show a striking new landscape of upturned layers of rock reminiscent of layered shales here on Earth. Some of them lie at angles to one another – what geologists call cross-bedding – that indicate a change in the rate or direction of flow of whatever it was that deposited the beds. In this case it’s likely water but could also be wind.

The rover used its ChemCam instrument to determine the rocks’ composition, but no word yet on what it is. One additional drive is planned this week before the rover team gets holiday break.

I found more pictures of the area at Curiosity’ raw image site which now has 31,570 images on file from the mission. Some of the photos take you in close for a down and dirty look at the rocks. Below you’ll find a sampling including a 3-D stereo photo. Additional Mars stereo images can be found HERE.

Raw image shows a closer-in view of layered rocks at the Shaler site. Click to enlarge. Credit: NASA/JPL-Caltech/MSSS

Tightly cropped view of pebbles at the Shaler site. These that may have been rounded and polished by flowing water like the ones seen earlier by Curiosity. Click to enlarge. Credit: NASA/JPL-Caltech/MSSS

A stereo image shows a rock outcrop called “Hottah,” cited as evidence for vigorous flow of water in a long-ago Martian stream. Use a pair of blue-red glasses to see it in 3-D. Click to enlarge. Credit: NASA/JPL-Caltech/MSSS

While northern hemisphere sky watchers will have to wait until March to get a good look at Comet C/2011 L4 (PanSTARRS), folks down under are keeping an eye on it for us. The comet has recently reappeared in the dawn sky low in the eastern sky in the constellation Scorpius the scorpion for observers in the southern hemisphere. At the moment, it’s still a little fuzzball around magnitude 9.5-10.

Comet L4 PanSTARRS on the morning of Dec. 18, 2012. The numbers are star magnitudes. Kaufman estimates the comet was brighter than 10th magnitude. Details: 200mm lens, ISO 1600. Credit: Rob Kaufman

Rob Kaufman of Bright, Victoria, Australia shared a photo of the comet taken on Dec. 18. If   L4 PanSTARRS follows brightness predictions, it could reach -1 magnitude or nearly as bright as the star Sirius low in the evening sky in mid-March. I can’t think of a finer way to introduce the new season.

Splendorous Saturn as seldom seen – Cassini wows again!

Saturn photographed in enhanced color while the Cassini spacecraft was in planet’s shadow. The moons Tethys (lower left) and Enceladus (right of Tethys) are also visible. Click to enlarge. Credit: NASA/JPL-Caltech/Space Science Institute

NASA just released a brand new picture of Saturn taken by the Cassini spacecraft as it sped through the planet’s shadow. The photo combines 60 images taken in the violet, visible and infrared (heat) portions of the spectrum. The last time the probe was at a sufficient distance from the planet and had the time to piece together a similar view was September 2006.

What a spectacle! Views like this are impossible from Earth since Saturn, located far beyond Mars and Jupiter, never passes between the sun and Earth. These photos were obtained on Oct. 21, 2012 from a distance of 500,000 miles with the sun behind Saturn.

Saturn in September 2006. Earth was visible at the time just above the ring plane. In the new photo, Earth is hidden by Saturn’s disk. The large outer E-ring is made of ice particles supplied by icy plumes erupting from the moon Enceladus. Credit: NASA/JPL/Space Science Institute

I don’t know why the mission team waited so long! We love this stuff. Lit from behind as it were, Saturn reveals details of its rings and atmosphere not discernible in more typical, front-lit images. Tiny ice particles in the rings flare into light from this perspective much like seeing someone’s breath against the sun on a cold day. Be sure to click on each picture to view the high resolution versions and revel in the glory.

New asteroid book good medicine for the doomsday blues

Don Yeoman’s new book on asteroids is a great read. Photo: Bob King

I just finished reading Donald Yeomans’ excellent new book “Earth-Approaching Asteroids: Finding Them Before They Find Us” and figured many of you might enjoy hearing about it. The book is published by Princeton University Press and available from Amazon for $15.73.

Author Donald Yeomans might be known to some of you already for his youtube video debunking 2012 doomsday predictions.  He works as a senior research scientist at the Jet Propulsion Lab, where he manages NASA’s Near-Earth Object Program Office. His book offers an excellent introduction to the layperson on near-Earth asteroids (NEAs), those objects that can potentially pass within about 29 million miles of Earth as they orbit around the sun.

Yeomans’ primary focus is on a smaller group within the NEAs called the PHAs or potentially hazardous asteroids. These pass within 4.65 million miles of the planet and span at least 500 feet across, large enough to cause significant destruction should they impact Earth. Close-approaching comets are also discussed.

The book is 161 pages long and divided into 10 chapters, starting with asteroid and comet basics and moving on to how astronomers calculate orbits and name names. Next is an overview of the new Nice model (developed in Nice, France) of the solar system’s evolution, where we learn that the giant planets did not form where they now reside.

Author Donald Yeomans

Gravitational interactions of Jupiter, Saturn, Uranus and Neptune with each other and the small asteroid-like building blocks of the solar system called planetesimals caused the outer planets to migrate over time. As they moved to their current locations, they scattered planetesimals hither and yon to form the current main asteroid belt between Mars and Jupiter and the distant Kuiper Belt beyond Neptune. It’s a fascinating read and goes far in explaining the present-day layout of the solar system.

With the Nice model as background, Yeomans delves into how asteroids from the main belt – the origin of nearly all NEAs – are delivered into Earth-crossing orbits through a combination of the Yarkovsky effect and gravitational nudges from Jupiter and Saturn. Heat absorbed by a rotating asteroid from the sun radiates back into space, giving it a little push and causing the asteroid to spiral toward or away from the sun – this is the Yarkovsky effect. Once the asteroid crosses into a “resonance” point with Jupiter or Saturn, it can then get tossed into the near-Earth neighborhood.

Because near-Earth objects, both comets and asteroids, are composed of primitive materials from early days of the solar system’s history, Yeomans believes they’re critical to understanding our origins. These small bodies may well have delivered much of the water and organic (carbon-containing) compounds necessarily for life to have evolved on Earth.

Plot showing the rapid increase in near-Earth asteroid (NEA) discoveries beginning in the late 1990s due to the increase in telescopic surveys and use of CCD technology. Credit: Alan Chamberlain, NASA-JPL/Caltech

The first near-Earth asteroid, 433 Eros, was discovered in 1898, while the first dedicated survey to hunt for them didn’t begin until 1973, when Gene Shoemaker and Eleanor Helin used the 18-inch Schmidt telescope on Mt. Palomar to search for small, fast-moving asteroids.

Yeomans describes accelerating efforts to find and track NEAs in the 1980s and 1990s thanks to workshops and papers by asteroid researchers, the discovery of the dinosaur extinction-asteroid connection and introduction of CCD technology (electronic cameras) that allowed for much more rapid and efficient surveys.

As scientists and legislators realized the potential destruction power of near-Earth objects, part of NASA’s budget was directed toward creating the Near-Earth Objects Observations Program in 1998. Its goal: to detect, track and characterize 90 percent of near-Earth asteroids 1 km and larger. The lower limit for an asteroid or comet to cause a global disaster is 0.9 miles (1.5 km).

Especially interesting is how the notification system works should a potential threat be detected during a survey run. I’ll leave it for you to read, but let’s just say, there are many checks before an announcement would be made.

Table from the book showing average asteroid impact results by size. Credit: Don Yeomans

Yeomans describes asteroids’ and comets’ compositions and how we might mine near-Earth asteroids for materials to build space ports and rockets. Much of our planet’s metal content long ago sank to the core or is otherwise deep beneath the surface. Asteroids wear their metals on their sleeves so to speak, with abundant iron, nickel and precious metals like platinum and rhodium much more easily available.

Later chapters go into detail about the potential threats of near-Earth objects, how orbits are refined through continued observation and the protocols in place should an alert need to be issued. Already about 90 percent of NEAs 0.9 mile and larger have been discovered; no known asteroids of this size will impact Earth for at least the next 100 years.

The final chapter describes what we’d do to deflect a potentially threatening asteroid. The slow-pull gravity tractor method (changing its trajectory by “towing” into a safer orbit via gravity from a neighboring spacecraft) and detonating a nuclear device on or near an asteroid are explored.

I highly recommend the book. Since it covers so many aspects of these fascinating asteroids, I found it comprehensive and a great read. While Yeoman covers a topic that some of us worry about, he provides the facts needed to stay cool yet informed. One very small criticism – a list of web resources on the topic in the index would have been nice addition.

I liked the occasional touches of humor, such as when the author wondered why there wasn’t a “rhodium” credit card yet, since that metal’s even more precious than the vaunted “platinum”. We’ll finish with the book’s final sentence:

“Near-Earth objects are among the smallest members of the solar system, but their diminutive size is in no way proportional to their importance. When it comes to their role in the development and future of humankind, next to the sun itself, theirs is the most important realm.”

GRAIL twins Ebb and Flow to smash into moon today

Artist’s rendering of the the twin washing machine-sized GRAIL spacecraft (Ebb and Flow) orbiting in formation above the moon’s surface. Tiny fluctuations in the strength of gravity over different parts of the moon change the distance of the two probes from one another. Credit: NASA/JPL-Caltech/MIT

NASA’s twin GRAIL (Gravity Recovery and Interior Laboratory) spacecraft have spent the last year mapping the moon’s hidden heart.

Today at 4:28 p.m. CST they’ll be intentionally crashed into a mountaintop near the lunar north pole. You might think this a poor use of a half-billion of your tax dollars, but the mission has been an astounding success.

Now that the paired probes are nearly out of fuel, mission controllers have directed them to the far north of the moon to avoid an unintentional crash near something important like an Apollo landing site.

Gravity map of the lunar nearside (left) and farside made by the GRAIL spacecraft. Red indicates where matter is more densely concentrated; blue corresponds to areas that are less dense. At left, the two big red dots are the lunar seas that form the “eyes” of the Man in the Moon. Thick layers of lava rock there create a stronger gravitational pull. Credit: NASA/JPL-Caltech/MIT/GSFC

Nicknamed Ebb and Flow, the GRAIL probes have been orbiting in tandem around the moon for nearly a year, peeling back the moon’s internal layers by mapping variations in its gravity field. As they fly over areas of greater and lesser gravity caused by both visible features, such as mountains and craters, and masses hidden beneath the lunar surface, the distance between the two spacecraft changes slightly. By measuring these slight variations in separation and combining that with accurate time and position information, scientists created the color-coded gravity map above.

Illustration showing the final flight path for NASA’s twin GRAIL probes, which will be crashed into the side of a mountain near the moon’s north pole this afternoon. Credit: NASA/JPL-Caltech/GSFC/ASU

The lunar twins discovered the moon’s crust is 21 to 27 miles thick or 6-12 miles thinner than previously thought. It also contains the same amount of aluminum as found in Earth’s crust.

Both findings confirm the moon’s origin via the “giant impact hypothesis.”  It’s believed the moon formed from materials launched into orbit when Earth was struck by a Mars-sized planet in the chaotic days of planet formation over 4 billion years ago.

“With this crustal thickness, the bulk composition of the moon is similar to that of Earth. This supports models where the moon is derived from Earth materials that were ejected during a giant impact event early in solar system history,” said GRAIL co-investigator Mark Wieczorek.

The moon at 4:28 p.m. CST this evening in the sunset sky. Created with Stellarium

GRAIL’s gravity map reveals familiar  lunar features like craters, mountains and lava plains, but with its unique ability to probe beneath the surface, the probes discovered a thoroughly fractured and pulverized lunar crust riddled with subsurface “linear gravity anomalies” more than a 100 miles long.

Impacting meteoroids and asteroids common during planetary formation 4.5 billion years ago created these deep cracks in the moon’s crust that later filled with lava and solidified into dense pathways of rock.

Says Jeff Andrews-Hanna, a GRAIL guest scientist with the Colorado School of Mines: “These linear gravity anomalies indicate the presence of dikes, or long, thin, vertical bodies of solidified magma in the subsurface. The dikes are among the oldest features on
the moon, and understanding them will tell us about its early history.”

While plate tectonics has recycled Earth’s early crust, other planets may still retain similar deep fractures attesting to the bombardment experienced during their formation long ago. Maria Zuber, the MIT geoscientist leading the GRAIL mission, thinks it possible that the cracks could have served as refuges for microscopic life on a planet like Mars when its climate changed from wet to the current cold and dry. That’s quite a wonderful thought really – that bombardment during the formation of the moons and planets created sanctuaries for life.

The impact strikes will happen on a mountain forming part of a crater wall near Anaxagoras crater. Credit: NASA

With the two probes now nearly out of fuel and orbiting only as high above the lunar surface as a jetliner, they’re on a collision course with an unnamed mountain near the crater Anaxagoras. The scene will be hidden in shadow at the time of impact. The first to go will be Ebb at 4:28:40 p.m. (CST) with Flow following 20 seconds later.

Map of the moon the way it will appear at 4:28 p.m. (CST) today at the time of the probes’ impact. The right side is the sunlit crescent moon; the dark area is still in shadow but will be faintly illuminated by light reflecting off Earth toward the moon. Credit: Virtual Moon Atlas

Slamming into rock at 3,750 mph, each probe will create a faint flash of light upon impact that might be visible through a telescope. Chances are slim, so don’t expect a big bang, but if you’re game to try, you can use the maps here to hone in on the impact location. Who knows, maybe you’ll see a tiny star-like point of light in the darkness at the appointed time. Observers on the East Coast are favored since the flashes will occur when the moon’s in a dark sky. For Duluth, Minn. and around the Midwest the sun will just be setting at that time.

NASA will provide live commentary of the scheduled lunar surface impacts beginning at 4 p.m. CST. Check out NASA TV or USTREAM to watch and listen. The Lunar Reconnaissance Orbiter (LRO) has already taken photos of the site before the crash and will photograph it soon after to record Ebb and Flow’s impact craters.

Visit the GRAIL site for more information about the mission.
UPDATE: Both craft crashed into the mountain at their appointed times. NASA plans to petition the International Astronomical Union (IAU) to name the impact site(s) in honor of Sally Ride, GRAIL team member and the first American woman in space. Ride died earlier this year.

Death Star moon Mimas meets its twin in Tethys

Saturn’s two “Death Star” moons – Tethys (right) with its 276-mile diameter Odysseus crater and smaller Mimas with its 86-mile wide crater Herschel. Credit: NASA

I originally planned a book review on a new asteroid book today but decided to hold off a couple days because of little time and other plans. Don’t worry, it’ll arrive in this space shortly. For fun I thought I’d share a recently released photo taken by the Cassini space probe of Saturn’s moon Tethys (TEE-this). This 660-mile wide ice ball orbits the planet every 1.9 days. In 6-inch and larger telescopes it’s a faint point of light hovering near the planet like a moth around a candle flame. Mimas is even closer to the great ringed one, zipping around it in just under a day.

George Lucas Death Star from the Star Wars movie series.

Both it and another Saturnian moon, Mimas (MEE-muss) have large craters that size and appearance-wise are a good match for the concave disks of the superlasers in the infamous Death Stars, the moon-sized battle stations built by the evil Galactic Empire in the Star Wars movies. Mimas earned the nickname Death Star moon years ago, but Cassini proves that seen from the right angle, Tethys is just as capable of going over to the dark side.

Both moons have densities indicating they’re composed mostly of water ice. That tells us something about how bitterly cold (about 325 below F surface temp) it must be at Saturn’s distance from the sun for craters blasted from ice to remain sharp and clear 4 billion years after their origin.

Flyby photos show lumps and bumps of far-out asteroid Toutatis

Composite of 9 pictures showing mulitiple Geminid meteors, including a -6 magnitude fireball, photographed from a mountainside above Coal Creek Canyon, Colorado. Each flash represents a grain or pebble of the asteroid Phaethon burning up in our atmosphere. Credit: Dr. Richard Keen

This morning two small asteroids passed harmlessly by Earth at distances of just 174,000 and 292,000 miles. 2012 XP134, the more distant and measuring 42 feet across, whizzed by at 8 a.m. (CST) and 40-foot -wide 2012 XL134 two hours later. While some may take the sign of so many Earth-approaching asteroids as a bad omen, it’s all good news in my view.

NASA estimates there are a total of about 10 million near-Earth asteroids in the 10-meter (32 feet) range with an expected impact rate of one every 10 years. If you up the size to 30-meters (100 feet), there are 1.3 million objects with an impact rate of one every 200 years. Objects this size are still too small to gouge a crater and cause significant damage on the ground. Most would be expected to fragment in an airburst and possibly drop meteorites along their entry paths.

This chart shows how data from NASA’s Wide-field Infrared Survey Explorer, or WISE, has led to revisions in the estimated population of near-Earth asteroids (NEAs). The infrared-sensing telescope performed the most accurate survey to date of NEAs. Small objects found weekly number in the millions. Click photo to learn more about asteroid numbers. Credit: NASA

With numbers like these, it’s no surprise that Earth-shaving asteroids are discovered routinely. According to Donald Yeomans, manager of NASA’s Near-Earth Object Program Office, asteroid search programs find about 20 every week. In tomorrow’s blog, I’ll be reviewing his brand new book on the topic.

I’m glad all these good people are watching out for flying rocks. Not only does it mean we humans are becoming more knowledgeable about our surroundings, but knowing their orbits allows us to forecast when one of them might pose a danger in the future. This, we hope, will stir us to devise solutions to avoid a potential disaster. In 1990 there were only 134 Earth-approaching asteroids known; as of mid-2012 that number is somewhere around 9,000 and rising every week. Wouldn’t you rather know what’s coming than be in the dark?

Flyby images of the 3-mile long asteroid Toutatis taken by the Chinese Chang ‘e 2 spacecraft earlier this week. Its odd shape might be the result of two separate asteroid fragments that stuck together after a gentle collision. Click for larger version. Credit: SASTIND via Weibo / UMSF

Many of us got to experience first hand this week what happens when minute pieces of an asteroid strike Earth’s atmosphere – a beautiful meteor shower! Thurday night’s Geminids originate from dust and small pebbles released from the 3.1 mile long asteroid 3200 Phaethon. Two nights prior to the Geminid peak, the largest near-Earth asteroid 3179 Toutatis, also about 3 miles long, passed some 3.4 million miles from the planet.

64-frame movie showing Toutatis tumbling through space only 4.3 million miles from Earth on Dec. 12-13. Credit: NASA/Goldstone radar

While Phaethon’s too faint for most amateur telescopes, Toutatis remains bright as it slowly travels through the constellations Cetus and Aries this month. I watched this star-mimic amble through my telescope field of view Thursday night while trying to appreciate exactly what I was looking at. Fortunately the Chinese and NASA’s Goldstone radar provided some help.

A cropped version of picture sequence shows a clearer view of the asteroid’s surface. The bumps could be piles of boulders. Credit: Chinese National Space Agency

As the spacecraft flew by the bizarre-shaped Toutatis at the relative speed of 24,000 mph, it snapped a series of approach pictures. Higher resolution images will soon be released, but these are clear enough to see what appear to be boulder piles strewn about the surface as well as shallow craters. We live in wonderful times.

Over 100 an hour – Gemmy Geminids don’t disappoint

A bright Geminid meteor slices like a knife across the top of Orion last night. 20mm lens at f/3.2, ISO 800 and ~ 3 minute exposure. Photo: Bob King

What a night for meteors! I hope you had clear skies like we did here in northern Minnesota. From an observing spot on a snowy road 15 miles from home I watched as 70 Geminids tore across the sky. Some took my breath away. They arrived often enough that I soon grew addicted to the sense of anticipation. You knew the next one was coming soon but never exactly where and how bright. Would it be a fly speck or one of the shower’s trademark yellow fireballs?

I saw ones that were so brief and bright they looked exactly like sparks flying from an arc welder. Others burned steadily for a full second or two, leaving glowing trails. There were brief bursts of 2-3 meteors, lots of singles and occasional odd meteor-less gaps lasting five minutes or more. What I wouldn’t have given for a second set of eyes in the back of my head.

Two meteors shoot out Gemini in this single time exposure made in Cloquet, Minn. Credit and copyright: Matthew Moses

Even in 0 F temperatures and with work looming in the morning, it wasn’t easy to call it a night. Matter of fact, it was impossible. I went to bed at 1 and set the alarm for 3:30 a.m. to catch the peak. What a surprise to wake up and see ice fog slowly enveloping the stars. I just about turned back to bed, but a meteor flash through the window was motivation enough to dress up and go out for one last head-craning look skyward. Glad I did. At that moment, the most brilliant fireball of the night fell out of Gemini, illuminating the fog like some monster Roman candle burst.

Jim Schaff of Duluth, Minn. got a nice shot of Geminid zipping through the Big Dipper this morning.

According to the International Meteor Organization’s quicklook data for the Geminids, the shower peaked at 132 meteors per hour early this morning. More activity is in store today and tonight as Earth passes through the tail end of debris left by the asteroid 3200 Phaethon. As for the other meteor shower forecast from Comet 46P/Wirtanen, I’ve heard only spotty reports. I saw only one suspect that may have been a member.

A green-tinted Geminid lights up a portion of the Ursa Major early this morning. Photo: Bob King

We normally have no sense of the Earth moving through space which it does every day at a clip of 18.5 miles per second. Not so last night. Seeing all those meteors fire up as our planet plowed through Phaethon’s debris cloud gave us a visceral sensation of Earth’s silent but swift circle around the sun.

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Face southwest about 40 minutes to an hour after sunset to see the crescent moon and Mars tonight. Created with Stellarium

On a final note, the crescent moon returns to the twilight sky tonight. Take a look low in the southwest about 45 minutes after sunset (around 5 p.m. for Duluth, Minn.) to see a very young 1-day-old moon. It’s not far from Mars, but the planet is so faint right now because of its great distance from Earth, you’ll probably need binoculars to spot it.