My apologies for such a long time since my last e-mail, but this one can’t wait: You should go out TONIGHT (or over the next couple of nights) and see Comet Holmes. It’s easily visible in the Northern hemisphere almost all night long. My kids and I just went out and saw it at 6:30 pm — right here in Boulder, even with the lights of surrounding houses. It’s visible to the naked eye, looking like a little round cloud. With binoculars, you can clearly see the bright, spherical coma. So go outside and have a look! A short Q&A:
Q: Where should you look to see it?
A: See the finder chart at http://www.skyandtelescope.com/observing/home/10862521.html; it’s currently very close to the brightest star in Perseus (Mirfak), which you can find because it is fairly close to the easily recognizable “W” pattern of Cassiopeia. If you are looking in the evening, this puts it in the northeast sky; once you find the bright star Mirfak, the comet is slightly down and to the left.
Q: What is it?
A: It is a comet, which is essentially a ball of ice mixed with rock and dust that orbits the Sun. Comets spend most of their orbits as frozen rocks far from the Sun. But when one happens to come in toward the Sun, the heat of the Sun causes ice to sublimate into gas, and dust to be released. This gas and dust forms a huge, roughly spherical “coma” around the central “nucleus” of the comet. It may then grow a tail — which will point away from the Sun — as sunlight and the solar wind blow some of the coma material outward. Comet Holmes does not currently have a tail.
Q: Has Comet Holmes ever been seen before?
A: Yes. It was discovered in 1892, and it orbits the Sun in just under 7 years — which means it has passed by us many times in the past century. However, this year’s pass is unusually bright, and it became bright quite suddenly and unexpectedly: It brightened by about a factor of 400,000 over the course of a single day (on Oct. 23/24)! You can find a nice article about it at http://www.space.com/spacewatch/071025-comet-holmes.html, and even more details on Wikipedia (http://en.wikipedia.org/wiki/17P/Holmes).
Q: What’s the difference between a comet and a meteor?
A: Ah, one of my favorite questions. People often confuse the two, but they are quite different:
+ A meteor is a flash of light in our own atmosphere, created as a piece of space dust burns up. Hence, meteors are visible for only a few seconds as they dart across the sky.
+ Comets are in space, orbiting the Sun. That means they are typically millions of miles from Earth, so they move only slowly relative to the stars; in a single night, you many not notice a comet moving relative to the stars at all, and will only notice that it rises and sets along with the stars that appear near it.
+ Despite these differences, there is a deep connection between comets and meteors: Most of the dust particles that enter our atmosphere to become meteors were actually shed by comets. That is, meteors are created by comet dust…
All for now. Happy observing!