October 2007 Archives

Finding the Comet

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Comet 17P/Holmes remains excitingly bright, and the shell of dust from its recent outburst is now large enough to be seen with the unaided eye -- it no longer looks at all like a star.

I took these photos back on Saturday, when the comet was still quite condensed, but as you can see in the upper image, there is distinct fuzziness even in a very low-zoom photo. (The stars appear as short lines because the camera was stationary for this shot, so the sky moved by a few arcminutes, comparable to the width of the comet's coma.)

Below, a wide-angle view of the sky looking northeast an hour or so after sunset. Very lightly processed to de-emphasize the Moonlight flooding the sky (the full Moon was hiding right behind the dome at bottom). Near the center of the image you'll recognize the triangle from the top photo, where the lower left object is the comet. At the very bottom is the brilliant white star Capella -- if you're looking for the comet under city lights, start by finding that. Even in the most light-polluted areas, it should be possible to spot this comet with binoculars (I'm looking at you, readers in New York).

Tonight the Moon doesn't rise for several hours after sunset, so the evening should be quite reasonably dark. Since we've got clear skies here, I plan to take the telescope for another spin, even despite the cold I'm battling.

Comet Holmes in Perseus as seen from the roof of the Physics Building here. Click either photo for a larger version.


Looking down the tubes of our refractor (and its finder scopes), out the slit, past the Moon, at a fuzzball three times as distant as Mars.

No, I haven't abandoned the blog. It's just been a busy, erm ... month.

Anyhow, Comet 17P/Holmes is putting on a show at the moment, what with getting a half-million times brighter in a matter of hours. Now it's about 48 hours later, and sky watchers everywhere are having a ball with it.

Obviously I can't let everybody else have all the fun, and I just so happen to have a century-old 10-inch refractor up on the roof and some history with astrophotography, so here's my contribution. (Click pictures for full-rez versions.)

We estimated the comet was at about magnitude 2.5 at the time, which generally agrees with the reports coming in, and looked to be about an arcminute across. Given that it's about 1.5 AU from us (three times as far away as Mars!) that coma is around 60,000 kilometers wide. If it's around 30 hours post-eruption in the picture below, that dust cloud is expanding at 600 meters per second. Reports indicate that it's expanded considerably tonight.

Conspicuously, there's no tail. For one thing, it'll take some time for the sun to sculpt this expanding cloud; for another, the tail would be pointed almost directly away from us, anyway. It's actually on its way out now, but it only has to get out to the orbit of Jupiter, so 17P isn't going anywhere in a hurry. Whether or not it stays bright, on the other hand, is anyone's guess.

17P-domezoom-071025.jpg 17P-widefield-071025.jpg
A closer look at the sky, and then a much closer look through the 10-inch.

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This page is an archive of entries from October 2007 listed from newest to oldest.

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