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October 30, 2007

Comet Holmes

Posted by John Baez

Have any of you folks seen Comet Holmes? It was just another boring little comet somewhere between Mars and Jupiter when it suddenly got a million times brighter on October 23rd, going from magnitude 17 to magnitude 2.8 in just a few hours!

According to the magazine Sky and Telescope, it’s easy to spot with the naked eye…

… in the northern sky near the easily recognizable Cassiopea:



One of the weird things about Comet Holmes is that, at first anyway, it had no visible tail:




Here’s how it’s grown since its initial burst into visibility — with an image of Jupiter artificially placed next to it, so you can compare their angular size as seen from us:



I’ll go out in the back yard and take a look. Let me know what you see!

Posted at October 30, 2007 5:36 AM UTC

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Re: Comet Holmes

Darn. Sort of cloudy… a mackerel sky, rather unusual for this time of year. I think I saw Polaris, but not Comet Holmes.

Posted by: John Baez on October 30, 2007 5:59 AM | Permalink | Reply to this

Re: Comet Holmes

From Wikipedia:

Crux is exactly opposite to Cassiopeia on the celestial sphere, and therefore it cannot be in the sky with the latter at the same time. For locations south of 34° southern latitude Crux is always completely in the sky.

Ergo, Cassiopeia never is. So the Australian category theorists are stuffed. (Actually Macquarie Uni makes it by nearly 14 whole minutes of latitude, but at this time of year, I doubt it’s enough.)

Posted by: James on October 30, 2007 11:58 AM | Permalink | Reply to this

Re: Comet Holmes

I’ve been watching Comet 17P/Holmes with my 11x80 binoculars since the night of the 25-26th with only one night clouded out in that period (the 27-28th). Despite excellent seeing conditions and a very dark site in rural Wisconsin, the prodigious light output of the near-full moon around perigee actually produced a detectable (blue!} raleigh scattering in the atmosphere which severely hampered observation of faint details over the course of the following observations. Nevertheless, Comet Holmes put on a magnificent display:

The comet appeared initially on the first night (25-26) as a compact golden-yellow fuzzball that was very slightly out-of-round (elliptical) in shape with the long axis roughly oriented north-northwest by south-southeast, with a very discrete and bright star-like nucleus that was slightly off-center on the long axis of the elliptical coma on the south-southeast side. I estimated the magnitude at this time to be about 2.6. A friend of mine who had contacted me by phone at that time was observing the comet with his 8-inch telescope at high magnification. He reported that he could detect a hint of an assymmetry near the nucleus that could be interpreted as a tail.

The next night (26-27) the comet appeared to be noticeably brighter by naked eye as well as in my binos - about 2.5 magnitude. The coma had also grown substantially in size - it appeared to have nearly doubled in diameter - and had become much rounder, although the central bright region near the nucleus maintained an elliptical or oval shape. The nucleus also appeared to be very slightly less point-like and there were hints of a very faint tail-like extension of brightness within the coma extending a short distance from the nucleus but not beyond the confines of the coma.

On the night of 27-28 I was clouded out.

The next night (28-29) the comet appeared to maintain its magnitude of about 2.5, and I could plainly see with my naked eyes that its formerly star-like appearance was now definitely “fuzzy”. In my binoculars I was astonished to see it had again grown considerably in size AND that there was additional structure: there appeared to be a bow-shock-like brightening on the northward margin of the coma. I was also able to detect a very faint and wide fan of brightening extending to the southwest away from the coma. The formerly point-like nucleus had degraded considerably into an oval-shaped spot with the same orientation as the earlier observations.

Last night I could plainly see with my naked eyes that the comet was a fuzz-ball that readily stood apart from the point-like stars in Perseus. In the binos I found that the coma had lost the apparent bow-structure I had seen the night before, and had become substantially more diffuse (as if the earlier concentrated nucleus had distributed irs brightness out into the surrounding coma). The very faint tail-like fan beyond the coma towards the southwest had degraded considerably but was still detectable. The nucleus itself now resembles a brighter version of the comet halo as it appeared in my first observation (25-26) in both size, shape and brightness WITHOUT the point-like nucleus. Yet the comet appears to be only very slightly slacking in its peak brightness. I estimate last night it was still around at least 2.5 or 2.7. But right now, to the naked eye, it no longer looks like a star: it’s definitely a fuzzball in Perseus!

As the Moon wanes it ought to get a lot more interesting!

Great site John!!!

Posted by: Anton Szautner on October 30, 2007 2:39 PM | Permalink | Reply to this

Re: Comet Holmes

On the NASA applet we see the comet is moving further away from the ecliptic, so I’m guessing us poor southerners aren’t going to see it any time soon.

Posted by: Kea on October 30, 2007 11:44 PM | Permalink | Reply to this

Re: Comet Holmes

The comet looked terrific on Halloween night from Nashville. Even better with binoculars.

My question is: will this view improve, and will it grow a cool tail? My kids are excited about comets, but only comets with tails. For a while every plane was called a comet until they learned “contrail.” Ok, I admit I like tails too.

Posted by: Stefan on November 2, 2007 10:24 PM | Permalink | Reply to this

Re: Comet Holmes

Advice for the internet generation’s eyeballs accustomed to photon intensity levels of a 100 watt lightbulb (aka a computer screen):

- Let your eyes adjust to your backyard’s dark level. Sit and wait a few mins before even looking for comet.

- When looking for the comet in Perseus (maps John links to above) make sure to “avert” your vision. Your peripheral vision is actually more sensitive to light than your direct focus. You’ll see the by-now fuzzy comet best if you don’t look directly at it. Astronomers are used to this focus trick. It works. It’s tried and true since Tycho Brahe.

Posted by: Jim Clarage on November 14, 2007 5:59 AM | Permalink | Reply to this

Re: Comet Holmes

The Astronomy Picture of the Day is a spooky photo of comet Holmes, taken from Hungary:


Posted by: John Baez on December 5, 2007 5:38 AM | Permalink | Reply to this

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