Comet ISON Ready for its Thanksgiving Date with Destiny

When it was discovered in 2012 as a new comet coming from deep space, some observers predicted Comet ISON would become so bright in our skies it would be the "Comet of the Century." Wiser heads knew, as comet hunter David Levy likes to say, "Comets are like cats. They have tails and they do precisely what they want!"

For a while, the comet seemed disappointing. But this week, on its way in to a close encounter with the Sun, Comet ISON started putting on a somewhat better show (as you can see in the image, taken by the skillful UK astro-photographer Damian Peach.) The comet now has two nice tails, one made of dust, the other of gas, pointing in the direction away from the Sun.

The comet is currently visible in the pre-dawn sky, but only barely and only when it's really dark. It's better with binoculars or telescopes. The excitement, however, is just beginning. Comet ISON is what astronomers call a "sungrazer" -- a comet that comes indecently close to our Sun. It just so happens, the closest encounter -- only about 3/4 of a million miles from the Sun's surface -- will be on Thanksgiving Day 2013.

The solid "nucleus" of this comet -- a chunk of frozen ices and rock -- is now estimated to be somewhere between 1/4 and 3/4 of a mile across. The Sun's heat could vaporize much of its ice and rock and the Sun's gravity could tear it apart into smaller chunks. Past sungrazing comets have had one or both of these things happen. So it could emerge from its date with the Sun one smaller but strongly evaporating comet, or as several comets spread out over a wider area, or as nothing more than a subtle trail of gas and dust.

If Comet ISON survives Thanksgiving, it will swing away from the Sun and emerge into our dark skies going northward from the plane of our solar system. Should there be enough of it left to make a show, that show will be visible to us in December and January. Around January 8th, for example, it will be near the north star, remaining in our view all night long. (But by then it will likely be much fainter.)

As we say on the radio, "Stay Tuned!" I will give you more updates on this interesting new visitor to our cosmic neighborhood in future posts.

If your want bulletins on Comet ISON between my posts, or need more technical information, see the "Current Status" page at NASA’s Comet ISON Campaign: http://isoncampaign.org/Present and then look around on that site.

[If you search the web for Comet ISON information, beware of the nutty websites predicting a collision with Earth or some other reason for the end of the world. The closest the comet will get to Earth is about 40 million miles on Dec. 26th. That's far enough that we can all sleep soundly at night.]

Crescent Moon and Venus Get Close Sunday Night Sept. 8

A minor, but cute, pairing is visible in the sky tomorrow. It happens soon after sunset and you can only see it if you have an unobstructed view of the west-southwest horizon. (For many of us that means we will have to get high -- only in the geographical sense, mind you!! Typically, our view is blocked by buildings, trees, hills, etc. and we can't see the western horizon.) But if you get to a place where you can see low in the west Sunday evening, you will see a very thin crescent Moon and the bright planet Venus just to the right of it.

You can start looking about a half hour after the Sun sets on Sunday and you'll see it best about 45 minutes after sunset. But don't wait too long to catch it; soon both objects will set in the West, and disappear from your view.

When Venus is visible just after sunset, people call it the evening star. But it's not a star at all, but a planet -- our neighbor planet just sunward of the Earth. It reflects quite a bit of sunlight both because it's close to the Sun and because it's covered with clouds that are quite reflective. (In fact Venus is so cloudy, there hasn't been a clear day there in 3 billion years. I like to cheer up my friends in Seattle by telling them that.)

As you can see in the nice diagram, which I borrowed from the good people at Sky & Telescope magazine, if you look further up and to the left, you will also see the planet Saturn in the same part of the sky. The distance in the sky between the Moon and Saturn should be about the width of your clenched fist, if you hold out your hand at arm's length. If you have binoculars or a telescope, you can enhance your view, but if you don't have an instrument, it's still fun to look. If you have kids, bring them outside and show them the sight too. It couldn't hurt to impress them with your knowledge of the universe while they are young.

For more information, you can see the full story at the Sky & Telescope web site: http://www.skyandtelescope.com/observing/highlights/Crescent-Moon-and-Venus-Put-on-a-Show-222505621.html