Naked Eye Comet!!!!
Published on Oct 25, 2007 at 1:52 am.
11 Comments.
Filed under comets, observing.
Wow. Earlier today, I read Tom’s posting that a comet had suddenly brightened. The comet in question is Comet 17P/Holmes. Normally, this comet is pretty dim and uninspiring. In fact, as recently as in the last few days, it was quite dim. Then, suddenly, the comet went into an outburst. The comet is now nearly 500,000 times brighter than it was just a couple of days ago! Sky and Telescope also has a short article about the comet, along with a finder chart. I have created my own finder chart here using the free planetarium program Stellarium.
Comet Holmes is normally pretty boring. It never gets particularly close to the Sun. It’s orbit goes from a bit beyond Mars to a bit inside Jupiter’s orbit, taking about 7 years to orbit the Sun. That puts the comet in the asteroid belt. It is generally quite dim, and you normally need a pretty powerful telescope to even find it. In fact, the comet was lost by even professional astronomers from 1906 until 1964. Just days ago, it was about magnitude 17. Now, it appears to be almost magnitude 2.5. That is simply amazing. The technical name for this phenomenon is outburst. In fact, the comet may have been in outburst in 1892 when Edwin Holmes discovered it. The comet brightened to naked eye visibility then, but it has been dim ever since. This time, it is considerably brighter, even, that it was in 1892.
I taught class tonight. We happened to have exceptionally clear skies here tonight (despite the fact that just a couple days ago they were forecasting clouds and a chance of rain!). So, after class, during our normal lab time, I took the students out to look at the comet. Even on campus, with lots of light pollution, and with a nearly full moon, the comet was easily visible to the naked eye. It appeared as an extra star in the constellation Perseus. In binoculars, it still looked pretty much star-like. But, in the telescope, it was clearly not a star. You could see a nearly star-like core to it, but there was a distinct bright fuzz around it. To me, it looked more like a bright large planetary nebula than a comet. There was no tail visible, though the core seemed to be a bit off center from the coma.
So, what happened? I don’t know. I am sure that this comet it going to be getting a lot of scrutiny. There are several possibilities, though. Comets shine primarily through reflected light from the dust and gas given off as the ices of the comet sublimate and are expelled from the nucleus. Comets have been known to break up, crack, or in some other way expose large amounts of fresh material to the sunlight. This fresh material then sublimates like crazy, throwing vast amounts of material out, thus making the comet look much brighter for a while. But, that is not something that you’d expect of a comet this far from the Sun.
Another possibility is that a large meteoroid ran into the comet. We see evidence of craters on some of the comets visited by spacecraft, so we know that they can be hit. A fresh impact would also produce an effect like we are now seeing. The comet is in the asteroid belt, so there are a few more things out there that it can collide with, but the comet nucleus itself is tiny in the overall scheme of things in the Solar System, so the likelihood of an impact is correspondingly tiny. It is more likely that the comet’s nucleus broke apart, cracked, collapsed, or whatever, even at Homes’ distance from the Sun. But, we should be finding out more as the days pass.
Now, I did not see a tail for the comet tonight, so you may be asking why no tail is visible. Comet tails point away from the Sun. Right now, the Earth is nearly between the comet and the Sun, so any tail would be pointed mainly away from us. But, more importantly, the comet is normally not very active, and has not been active recently (until this outburst), so there is not much material with which to make an impressive tail. Comets at this distance from the Sun often don’t have impressive tails (but they also don’t get this bright on average, either). So, with the outburst, it is possible that enough material is being thrown into space to make a decent tail. It will still be pointing largely away from us, so don’t get your hopes up for seeing a huge tail. However, it is possible that over the next week or two, a small tail might develop. At any rate, the comet bears watching.
Incidentally, this is the second unexpected naked eye comet that I’ve seen this year. The first one was Comet McNaught in January. That one was also surprisingly bright, but at least it took a bit more time to get so bright. Comet Holmes seems to have gotten much brighter much quicker, so that suggests some drastic event happened on the comet. Only time will tell what that event may have been.
Given that the comet is naked eye, I’d encourage everyone to go out and look. For those new to astronomy, and for teachers and students, if you watch night after night, you will notice that the position of the comet slowly changes in the sky relative to the stars of Perseus. This is a great learning and teaching opportunity.
-Astroprof
Astroprof’s Page » Comet Holmes Update on October 26, 2007 at 10:44 am: 1
[…] So, if you want to go looking for the comet, it is still very close to the position marked on the finder chart that I prepared for my previous posting about the comet. […]
Steve on October 26, 2007 at 12:41 pm: 2
Nice article, thanks for the info. Downloaded Stellarium … wow, what a nice program!!
Joey Gibson on October 26, 2007 at 9:57 pm: 3
I’ve been using Stellarium for a while, but this comet doesn’t seem to be listed. How did you add it? Can you post the file(s) you used to add it? I’d like to get it in my copy of Stellarium.
Astroprof on October 27, 2007 at 3:49 pm: 4
Actually, I got the star field using Stellarium and manually added the approximate position of the comet afterwards. I am new to Stellarium myself, and I have yet to figure out how to add objects to it.
Astroprof’s Page » Comet Holmes’ Tail on November 2, 2007 at 5:44 pm: 5
[…] Undoubtedly, what has happened with Comet Holmes is that some major event (either a collapse of a hollow portion of the comet, or perhaps an impact event) created a sudden explosive release of material. The frozen gasses sublimated like crazy, and there are likely to be all sorts of jets streaming from the nucleus of the comet right now. The dust cloud expanded away from the nucleus. Most of what we are seeing is the dust cloud. It reflects a sort of yellow light because that is the color of the Sun. Both the gas and the dust are being blown back to form tails. The tails are short because the event that created them is scarcely a week old. Comet Hale-Bopp, and other comets with famous long tails, had a long time to generate those tails. Holmes is just getting started. The ion tail is dim and it is pointed almost straight away from the Sun. Earth is nearly between the Sun and the comet, so don’t expect to see much of the ion tail. However, the dust tail tends to be much brighter anyway, and it will curve a bit. In my first post about the comet, I said that we might begin to see a bit of the dust tail as it forms and curves away some after a week or so. It looks like that has now begun to happen. Still, the tail is far, far less bright than the coma, where there is still an amazing amount of material that has been blown into space. And, the tail is still pointed mostly away from us, so it is severely foreshortened. But, as the photo at the top of this posting, and several others at the Spaceweather.com comet gallery as well as the Sky and Telescope comet gallery show, the tail is now starting to show up. […]
Astroprof’s Page » Comet Holmes is suddenly news (after 2 weeks) on November 6, 2007 at 12:27 am: 6
[…] Wow. Back on October 24, almost two weeks ago, I heard about the sudden outburst of Comet 17P/Holmes. I wrote about it hours after observing it. There was quite a bit of news about the comet around the internet. Just over a week ago, I posted a photograph of the constellation Perseus, with the comet marked. This has turned out to be one of the brightest comets in a long time, second only to Comet McNaught early in the year. Comet Holmes was clearly visible to the naked eye. Now, as it expands, it is getting harder to see, as I explained recently. And, in all those nearly two weeks, the comet has been virtually ignored by the news media. I saw a brief mention in USA Today, but that was all until Sunday when an amateur astronomer associated with a planetarium in the area wrote about it in the monthly column for the local paper. Then, I see this today. Yeah, they are sure on top of things. […]
Neg on December 10, 2007 at 6:52 pm: 7
Is this comet what I just saw tonight? There was a bright (as bright as a planet) distinct dot with a wide, fan tail almost directly overhead here in S.Florida at about 6:45pm. By 7pm it had faded to a blur, and by 7:15pm was gone completely. I’ve been looking around online for what it was and this seems to be it? It was near Cassiopeia. Even with city lights, it was a spectacular sight.
Astroprof on December 10, 2007 at 9:32 pm: 8
No, that was not the comet. I don’t know what you saw, but comets don’t change that quickly. It sounds like an atmospheric phenomenon of some sort.
shelley on December 11, 2007 at 6:05 pm: 9
Neg, I live in Cape Coral, Florida. I too saw this, as did my mother who lives in West Palm Beach - 200 miles away. I do not know what it was, but I guess we got lucky to see it. I saw it in the same vicinity of Cassiopeia, right over head of my home.
Neg on December 11, 2007 at 6:58 pm: 10
After more research online and much talk around the water cooler, I think it was maybe a meteor from the Geminids? I’ve read that they are peaking this week and sometimes one will be visible a long time. Maybe it was less than 1/2hr. that it was visible and it just seemed longer b/c it was so unusual. Still, it was longer duration than other meteors, and white instead of green.
Shelly, thanks for posting so I know it wasn’t just a local phenom! I’m in Jensen Beach, north of WP but south of you.
Astroprof on December 11, 2007 at 7:29 pm: 11
Once in a while a fireball will leave behind a lingering train in the upper atmosphere that can be visible for quite some time after the meteor itself is long gone. So, you may be right, that could be something left by a Geminid.