Comet Holmes’ Tail
Published on Nov 2, 2007 at 5:43 pm.
2 Comments.
Filed under comets.
Comet Holmes is now showing a tail. A hint of the tail can be seen in the following picture taken by Norway’s Mikkel Steine and posted to the Spaceweather.com comet gallery. The tail is very faint, but it can be seen pointed off to the right in the photograph. The tail is visible in the photograph because of the length of the exposure. It is not visible to the eye, even looking through the eyepiece of a telescope, so don’t even get your hopes up for seeing it with the naked eye.
So, what is going on with this tail, you might ask? Well, first of all, you need to know what a comet’s tail is all about. The comet itself basically starts with a small chunk of material that is a mixture of ice, frozen gas, and rock (or dust). When it gets close to the Sun, the frozen part of the core begins to heat and sublimate, blowing material out all over the place. The gasses and dust blown from the nucleus form a cloud around the nucleus. The head of the comet is the densest portion of the cloud, and it is so dense that you can not even see the nucleus from afar. The coma is the head of the comet, and it is composed of the rest of the cloud around the head of the comet. But, the comet itself has very little mass and thus very little gravity. It can not hold onto this gas and dust. So, the solar wind blows away the gas to form an ion tail (or gas tail) streaming out almost directly away from the Sun. This gas tail is normally a definite blue color.
The dust tail, though, is composed of particles that are pushed out by the light pressure from the Sun. These small solid particles continue to orbit the Sun, only in orbits a bit farther out than the comet, and thus a bit slower. So, the dust tail tends to not point directly away from the Sun, but rather curves a bit, as seen in this diagram:
An example of both types of tails seen in a comet is in the following photograph of Comet Hale-Bopp taken by Jerry Lodriguss and posted on the Astronomy Picture of the Day this past spring.
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.
It has been cloudy here for several days, but tonight it is clear. So, I am going to go look at the comet again in a few hours, once it gets good and dark and the comet is up high in the sky. This comet remains bright enough to be seen from the light polluted skies of the city, though it is obviously better in dark skies. The coma has been expanding, and it is definitely visible as a fuzzy ball even in binoculars. So, if you have not seen the comet yet, grab a pair of binoculars and go look. Even with the naked eye, you can see the comet as a fuzzy star near Perseus. Look at the finder chart on my first posting, or look at the photograph that I took this past weekend to find the comet. You don’t want to miss this sight, since comets this bright are rather rare. It is really amazing, though, that we have had two bright comets in a year’s time. Many ancient people thought of comets as harbingers of evil, so two bright ones within a year would have really freaked them out.
-Astroprof
GEMACHESNEY on November 3, 2007 at 8:45 pm: 1
the greatest comet for everyone to see and there is nothing on the news!
Surfing the Tao » Notes from the Surf XIV on November 3, 2007 at 10:25 pm: 2
[…] Comet Holmes still getting brighter and now has a tail. Check out this photo gallery. […]