Comet SWAN

10/17/06 – 10/23/06
by C. Zaitz

There’s a comet in the sky, and its name is SWAN. It’s time to dust off those binoculars and point them halfway between the bowl of the Big Dipper and the bright star Arcturus in the evening sky. If you want to find Arcturus, you can trace an arc off the handle of the Dipper and “arc to Arcturus.” Both Arcturus and the Big Dipper will be skimming the horizon, so if you happen to sport tall trees or a roof to the north, you might not spot the comet.

Many of us remember the comets of 1996-7, Hyakutake and Hale-Bopp. They were fabulous and awe-inspiring. I was living in Yonkers, NY at the time, and remember lying on the hood of my car in the chill Westchester air, feeling the warmth of the engine and seeing the comet streaking its enormous glowing tail across the sky. You might remember where you were when you saw the comets, too. It’s rare to have two such beautiful naked-eye comets in the sky within a year. Comet SWAN is not in the same league with those comets, but it’s always interesting to spot one in the sky.

It’s not hard to make a “comet.” We can start with something to represent the nucleus, or the heart of the comet. Spectral analysis has identified major ingredients in comets: Water, ammonia, organic molecules, and silicates. For silicates, we can use sand, dirt, or my favorite: kitty litter. Then add a little ammonia. A good squirt or two of Windex will do. For the organic molecules use whatever is handy; Karo syrup, sugar, or a leftover can of Coke. Pour all those ingredients together and what do you get? A mess, and a very warm comet. We forgot the ice! Comets are cold. They live in the outer regions of the solar system, so far from the sun that they have remained relatively untouched, unmelted and unsullied for the lifetime of the solar system, some 4.5 billion years.

So to make a comet, it’s handy to have a tank of liquid carbon dioxide. You could use regular ice, or you could get a chunk of dry ice from a local supplier, but the beauty of the pressurized tank of liquid CO2 is when it shoots out the nozzle, the pressure is released, it expands rapidly and gets very cold. It becomes dry ice snow, which is easier to play with than a chunk of dry ice. You can grab handfuls of it (wearing thick gloves, of course!) and smush it into your comet. A little water for sticking and mixing purposes, and you’ve got a pretty, dirty, cold and steamy comet. As it melts, the dry ice sublimates to gas and makes a bit of a comet tail. Perfect!

When you look at comet SWAN through binoculars, you will see a bright nucleus and perhaps the fuzzy tail. The comet has just journeyed around the sun, so its tail is prominent. By the way, comet SWAN is not just another pretty bird in the sky. Its name comes from the Solar Wind ANisotropy experiment which first discovered it. We’ve noticed that instead of being the same everywhere (isotropic) the wind behaves more like a plasma ball- the kind you see in a novelty store, with filaments and structure. You can think of the comet’s tail being swept back by that solar wind as you peer at it in the night sky.

Until next week, my friends, enjoy the view!