Sky debris fun to see – but don’t let it fall on you

This simulation shows asteroid 2012 DA14 passing through the Earth-moon system. Perhaps the next newsworthy sky features are two comets. Enlarge photo

NASA, JPL-Caltech/Associated Press

This simulation shows asteroid 2012 DA14 passing through the Earth-moon system. Perhaps the next newsworthy sky features are two comets.

Greetings stargazers.

It will be hard to write this month’s article without mentioning the recent event in Chelyabinsk, Russia, so let’s get that one out of the way first.

Yes, it was a coincidence that it happened while everyone was waiting for asteroid 2012 DA14. My personal coincidence, however, was that I had just discussed asteroid impacts in my astronomy class, including a photo from the 1908 Tunguska (in Siberia) event that was the last known major strike. I say known, because chances are good that there have been others that were missed because they happened to be over the ocean.

When the solar system was forming, 99.9 percent of the mass ended up in the sun. Most of the other 0.1 percent is in Jupiter. That doesn’t leave much mass for the rest of us, and even less for all the debris that hasn’t yet made planet-fall. However, there is still enough debris to make you want to duck occasionally.

This debris can roughly be divided into two groups based on density – comets and asteroids. Comets are made of the lighter stuff, such as water, that can turn to gas more easily when exposed to sunlight. (Think of evaporating snow – comets can be thought of as dirty snowballs.) These don’t survive very long when they are as close to the sun as we are, so we are left with the denser, rocky stuff, for our solar neighbors. Fortunately for us, most of these asteroids have already collided with something.

The comets are relegated to the colder parts of the solar system, far away from the sun. If a comet’s orbit brings it near the sun, we can see the sun reflected on the outgassing materials.

The periodic, or repeating, comets are members of the Kuiper belt. The most famous of these is comet Halley. Pluto is also a Kuiper belt object.

Comets that have much longer periods, so that we have only observed them one time, come from the Oort cloud, which is far beyond any of the planets. We should be able to see two of these Oort cloud visitors in 2013.

This month

Comet 2011 L4 (PANSTARRS), is now a Southern Hemisphere binocular object. But in early March, it should be visible in the western sky just after sunset. Because comets are notoriously unpredictable, it may or may not be visible to the naked eye.

The bigger show is expected later this year, with comet ISON. ISON could be the “comet of the century,” but most forecasters are hesitant to label it as such. If you are not old enough to remember comet Kohoutek (1973), the last “comet of a lifetime,” try Googling “comet dud.”

Right after dark, the constellation Auriga, the charioteer, is near your zenith. Your zenith point is the point directly overhead. Auriga is dominated by the bright star Capella, which was one of the points of the winter hexagon I wrote about last month. I don’t know what a charioteer looks like, but I think of the overall shape as a flat tire.

There are several open clusters that are worth looking at with binoculars, or even better with a small telescope – M36, M37 (my favorite of the bunch) and M38.

hakes_c@fortlewis.edu.

Charles Hakes is an assistant professor in the physics and engineering department at Fort Lewis College and is director of the Fort Lewis Observatory.