Comet 17/P Holmes update

Comet 17/P Holmes update

Comet 17/P Holmes update

Bad Astronomy
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Oct. 28 2007 9:06 PM

Comet 17/P Holmes update

I just went outside to look at Comet Holmes. Wow, it's changed in two days.

For one thing, it's expanded a lot. I can see it's not a star just with my unaided eyes! It looks distinctly fuzzy.

Phil Plait Phil Plait

Phil Plait writes Slate’s Bad Astronomy blog and is an astronomer, public speaker, science evangelizer, and author of Death From the Skies!  


Through the 'scope it's changed a lot as well. I took a bunch of pictures, but my equipment isn't up to snuff. Here's the best one:

This is a time exposure and my 'scope doesn't track, so the image is a little blurred. You can just see in the image that the expanding debris has taken on a decidedly shell-like appearance (through the eyepiece this is really obvious). It's brighter toward the edge! That's a classic shape for something like this. As the debris expands, you see it brighter near the edges, because your line of sight intersects more debris toward the edge. Here is an excellent image of Holmes showing this.

The nucleus is slightly off-center to the shell. I am starting to suspect that this is not a shell of debris, but a jet or beam of debris that happened to be aimed either right toward us or directly away from us. That's why it looks round. It must be 100,000 miles across by now. Wow.

Also, a star-like object can be seen above it-- that's the streaked line above the nucleus in my image. I originally thought that might have been a chunk that came off the comet, but now I think it's just a background star. I'll be going out to re-observe in an hour or so and that'll make it clear. If it moves with the comet it's a piece, if it stays put and the comet moves away from it it's a star. Edited later to add: Yeah, I'm pretty sure it's a background star; the distance between it and the nucleus has clearly gotten bigger in two hours.

So this is the comet that keeps on giving! I think it will start to fade soon; as the debris expands it gets thinner and less able to reflect sunlight. Eventually it will disperse and fade away completely. But it's stayed bright for three days now, and, with the Moon rising later every night, this is your best chance to see it! If you live near an observatory or University (in the northern hemisphere or not too far south fo the Equator), see if they have a viewing of it. You'll be glad you did.

And I am really looking forward to better images taken tonight. This is really an amazing object.