Saturday, July 08, 2006

Close Knit Stars

7/9/06 – 7/15/06

I love to knit. I learned to knit at Mount Holyoke* College. If you say it fast, it sounds like “Mentally Ill College.” At least that’s what I thought when they called to accept me. I hesitated until I realized who it really was. Mt. Holyoke had a January term, where you could spend a month goofing off, learning to knit, or taking an internship somewhere like Nantucket Island at the Maria* Mitchell Observatory, plotting the light curves of a variable star called DL Cas in the constellation Cassiopeia. I chose the latter. I had already learned to knit watching Moonlighting on Thursday nights with the girls in Ham Hall.

On Nantucket I lived on hot dogs and sauerkraut, shivered along the frozen beaches of a deserted resort island, and studied glass photographic plates of a variable star. The big question I was there to solve: was the “light curve” (its dimming and brightening pattern) of this star changing or remaining stable. Plot after plot, I couldn’t conclude that the light curve was changing. How unsatisfactory. I read my article in the A.A.V.S.O. recently and I didn’t understand half the stuff I wrote. It sounded like a big non-issue.

But it is an issue. Many stars are somewhat variable for a few reasons. Supergiant stars sometimes get brighter and dimmer because they are huge and are shrinking or expanding, trying to survive by “burning” whatever they have left in them after hundreds of millions of years of hydrogen fusion, holding out against the inevitable crushing force of gravity. These are called Cepheid stars, and it has been found that the period of variability of these stars is directly related to how bright they are. Once you find a star’s period, you can figure out its distance by knowing its intrinsic brightness. Thus these stars act as celestial rulers in figuring out distances to objects.

Other stars have different excuses for being variable. Two stars can be knit together with gravity like those mittens held together by a cord. One star might be a medium sized star like the sun, but it might be in orbit with a massive star or a shrunken dwarf star. If it happens that a double star system is at the right angle, we can see the bright star dim for a few hours or even days as the companion star passes in front of it, blocking some of its light.

If you’d like to see a beautiful double star system, find the three stars of the Summer Triangle. The most northwestern star is called Deneb. If you look closely you can trace the shape of a cross, with Deneb at the top. The bottom of the cross is in the middle of the triangle, and is a “star” called Albireo. Through a small telescope, you’ll actually see two stars. One is a brilliant blueish star, and the other actually looks golden. Even though I didn’t go to U of M, I can appreciate the beauty of those two colors next to each other. (Sorry State alums, there are no green stars!) These close knit stars are one of the many beautiful sights to see this summer.

Until next week, my friends, enjoy the view!

(* - pronounced “Whole-Yoke”, and Maria rhymes with pariah. If the representative had pronounced Mt. Holyoke correctly, I wouldn’t have thought the funny farm was calling for me…)

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