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Welcoming visitors and comets

I have recently updated this site to use a new content management system. This should make it a lot easier to find things, make site updates, and use this site as a record of observations I make. I have kept all the material from the old version of this site, so it should be possible to find old favorites.

Recently, I welcomed Comet Schwassmann-Wachmann 3 (a.k.a. Comet 73/P Schwassmann-Wachmann) into my back yard. As you may know, this comet has fragmented, rather like Comet Shoemaker-Levy 9 which hit Jupiter in 1994. There are currently dozens of fragments, in a huge range of sizes. The two largest fragments, "B" and "C", are easily visible for the next few weeks in small telescopes, and one or two of the others are in range of really big amateur scopes.

Last night I saw both of the large fragments in my small refractor (100mm, f/6 -- nice wide field views). Fragment "B" was a little easier to see -- I think it's more condensed, and so has a higher surface brightness. This was especially important with an almost-full Moon not far away! More details below...

At the time (10:35 PM MDT, or 04:35 UT 11 May 2006), fragment "B" was in eastern Lyra, a few degrees east of the 4th-magnitude star Eta Lyrae. In fact, in the telescope it came very close to a 6.8 magnitude star, HD 181878. Here's a chart of the field in question. It's left-right reversed, to mimic the field of my telescope, with the comet's position marked with a red "X":

Fragment B's position, late on May 10th, 2006. Eta Lyrae is the bright bluish star to the lower left. HD 181878 is the brightest star of the ones very near the fragment; it's above, and very slightly to the right of, fragment B's position.

When I defocused HD 181878's image, the comet was comparably bright. This suggests that fragment "B" might be slightly dimmer now (about 7th magnitude) than it was just a day or two ago (May 9-10), when people more often estimated it closer to 5th magnitude. However, moonlight makes it hard to be completely sure.

It became clear after about a minute or two that fragment "B" was moving. In fact, for a few minutes it occulted a faint (about 11th magnitude) star.

A little later, I found fragment "C". It was tougher, mostly because it was lower, and possibly a little more diffuse. I had no good comparison stars, but I suspect it was similar overall in brightness to "B".

I didn't try any of the other fragments. Fragments "G" and "R" have been reported around 13th magnitude. That's way too dim for the little 100mm, even without moonlight. Conceivably, they might just be in reach of my 12.5" scope once the moon is out of the picture, but that won't be for a week or so. Furthermore, fragment "G" appears to have fragmented itself, meaning it may be hard to follow after a while.

It seems quite possible the comet will follow the lead of comet Biela in the 19th century -- eventually, it might break up so completely that it can't be seen any more. So, got out there and catch this comet while you can!


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