Thursday, November 15, 2007

Comet 17P Hunka Hunka Burnin' Love

OK, so its real name is Comet 17P/Holmes, but sky watchers everywhere--myself included--are in a frenzy over this rock star of a comet. It blazed onto the solar system scene in late October by jumping 14 magnitudes of brightness in under 24 hours and becoming visible to the naked eye. Now that’s climbing the charts.

Riding high against the backdrop of the constellation Perseus the Hero, the fuzzy-headed phenom is easy to spot if you know where to look. Let’s get started.

1. You’ll need to be away from city lights to see the comet naked eye. Even if you have binoculars or a telescope, a dark sky is still best to see the star patterns that will lead you to the comet.
2. Plan to look for the comet after moonset, as the bright Moon washes out the sky and makes it difficult to see faint objects and star patterns. The Moon is currently increasing in illumination and setting later each night, as it advances toward Full Moon on November 24. If you’re not a night owl and can‘t wait up, it might be easier for you to get up a couple hours before sunrise to comet watch. Get the sunrise/set and moonrise/set times for your location at the U.S. Naval Observatory website.
3. You’ll need to know where north is. If you don’t have a compass, aren’t that familiar with your viewing location, or are just directionally challenged, determine north by watching where the Sun sets at your viewing location. The spot where it touches the horizon is approximately west, and if you stand with your left shoulder to the west, you will be facing roughly north. Take note of a natural or manmade landmark that lines up with the direction you’re facing, so you can re-orient later when you begin your comet hunt.
4. To begin, face north and look for a distinctive W-shaped star pattern, which is the “Lazy W” of the constellation Cassiopeia the Queen. The rather shallow W will be found about halfway between the horizon and the zenith (the point directly above your head). It may be a bit east or west of north, depending on what time you look for it. The W is about a fist and a half wide, if you hold your fist at arm’s length against the sky and measure along the widest part. The Lazy W will begin the night standing on end, balancing on the leftmost star of the W, as shown on this helpful star map from Throughout the night--because the Earth is always spinning--this view will change. By morning, the Lazy W will appear to have flipped over and will be balancing on its rightmost star. To simulate this apparent movement of the constellations throughout the night, simply print out the star map and slowly rotate it counterclockwise until you have flipped the Lazy W and the top of the map is now at the bottom. If you start observing in the middle of the night, about halfway between sunset and sunrise, you should see the Lazy W upside-down and looking more like an “M.”
5. After you’ve found the Lazy W in the sky, continue to face north and match its orientation in the sky on the star map, by rotating it counterclockwise. Now check the rotated map to see where Perseus should be in relation to the Lazy W. Then try to find Perseus in the sky.
6. If you’re having trouble finding Perseus, try this trick. Number the five stars that make up the Lazy W (not the upside-down M) from left to right. Draw an imaginary line between star #3 (the middle star) and star #2, extend that line below the W, and keep going straight until you reach a fairly faint star. This will be the first star in the four-star chain that makes up the ‘backbone’ of Perseus. The third star in the chain, noticeably brighter and more golden-colored than the others, is Mirfak, the brightest in Perseus (pronounced MURF ock). Right next to Mirfak is a faint, fuzzy looking patch and--you did it! You found the comet!

Even in my petite 10x24 binoculars, the comet looms into view as a large fuzzy blob next to Mirfak’s brilliant golden point. The ‘fuzz’ is the comet’s coma, the expanding cloud of dust and gas that envelops the comet when it is near the Sun. A comet is essentially a hunk of dirty ice, and the Sun’s heat vaporizes the outer layers of the ice. As the ice becomes gas, trapped dust is released. In small binoculars, you can see that the inner coma is denser and brighter than the outer coma.

In beefier binoculars like 10x50‘s--or in a small telescope--you begin to see the elongated shape of the bright inner coma, as well as some background stars coyly shimmering through the gossamer outer coma. See if you can discern any color in the coma; many observers are reporting a dull gold or pale green hue. You may also notice the sharp leading edge of the comet, which indicates its heading, as well as the fuzzier trailing edge, where the comet’s tail originates. Currently, there is no clearly visible tail because we are viewing the comet nearly head on and can’t see much of the tail that streams out behind it.

If you don’t have observing equipment but are hankering for a magnified view, check with your local astronomy club, planetarium, science museum, or nature preserve to see if any telescope observing events are scheduled.

Whether gazing at the comet naked eye, through binoculars, or with a telescope, everyone can appreciate its magic. Here are a few things to ponder while you commune with the comet:

- The word “comet” comes from the Greek word for hair. In ancient times, comets were known as “hairy stars.”
- All of the comet’s illumination is light from the Sun reflecting off dust and gas in the coma. The comet has no light source of its own.
- The comet’s nucleus, that is, the hurtling hunk of ice inside the expanding coma, is around two miles in diameter.
- All the stars you see near the comet--and in fact all the stars you see in the night sky--are in the Milky Way, our home galaxy. The comet is much much closer to us than any of those stars, which are all light years beyond our solar system. The comet is a solar system body, currently about 150 million miles away, in the asteroid belt between the orbits of Mars and Jupiter.
- Comets begin their long, strange trip around the Sun from the outer reaches of our solar system, in either the Kuiper Belt (pronounced KIGH purr) or the Oort Cloud. The Kuiper Belt is a huge ring of small bodies beyond the orbit of Neptune. The Oort Cloud is a vast sphere of comets that encases the entire planetary solar system.
- There are, conservatively, one trillion comets on the move in the Oort Cloud. That‘s right, conservatively.
- A comet’s orbit around the Sun can take a few years or a few million years. It will spend all or most of that time as a homely hunk of brown ice drifting through silent space. Only if and when its orbit takes it near our Sun does it make a spectacle of itself, like the effervescent Comet Holmes.

Yes, it dances for us. Can you feel the love?