Comets - Broom Stars and Dirty Snowballs
What exactly is a comet?
Comets are just fascinating to me. Astronomers like to learn more about them, not just because they are so cool and interesting but because they likely some of the most primitive bodies in our solar system. We don't know 100% for sure, but it is thought that comets seem to originate where there is a large reservoir of comets. They say that it is on the outer edges of the solar system. This location is a place called the Oort Cloud.
Many astronomers say that this "reservoir" was created during the same time the planets were coming into existence. Since that time, things have stayed somewhat the same and so its interesting to learn more about this area. It can hold the key to understanding more of the solar system and its origins for those that stick strictly to science for such things. Many parts of the solar system have changed over time, and the keys to why this is, may be found in part in the Oort Cloud and the surrounding area.
What exactly is a comet? Since they are made up of mostly of a mixture of ice and dust, many have come to call them dirty snowballs. In the outer solar system, where it is dark and cold, they remain in their frozen state. It is when they begin to move around and travel toward the Sun that they begin to absorb some of the Sun's heat. The comets that have been seen are visible when their icy surface begins to melt and evaporate. When this happens, gasses are released and then there are clouds of vapor that result.
This gas kind of spurts out along with dust. These jets of gas form a kind of cloud around the more solid part, also known as the nucleus of the comet. This cloud is what the light reflects off of, so that humanity can observe it. As for perspective, this cloud of gas can measure up towards hundreds of thousands of miles across! The nucleus of the comet itself is generally a few miles across, which is no small thing.
How does a comet get its shape?
As the above process continues, there is pressure involved which comes from the radiation of the Sun. This pressure forces the dust in the comet away from the head of the comet or "coma", and this is what gives it its fan shaped appearance. It begins to have a yellowish tail that is fan shaped. The solar wind plays its part as well. This makes the particles glow, and even forces those particles into another tail called the "ion tail". Ions are particles that are electronically charged. The biggest of the comets are known to have tails that can be one hundred million miles long!
The Hubble Space Telescope have given us some great images such as the Shoemaker-Levy 9, and comet Schwassman-Wachmann 3. This second comet was literally coming apart before their very eyes as they observed it. I think that is just fascinating and so wonderful that the image was caught for all time after that! Other ones observed are Comet McNaught discovered by Robert McNaught, and Hyakutake. Of course we are thankful to the discovery way back of Halley's Comet. We can expect the next visit from Halley's Comet in the year 2061.
To those wondering about the mention of Broom Stars, that goes way back to over 2500 years ago when by the Chinese. They called them Broom Stars, and the ancient Chinese called them "vile." They were not alone however, as others were superstitious of them as well, thinking comets were a bad omen, or even a "portent of evil", like something that might bring diseases or drought.
Would be interesting to get to update this in 2061! Who knows, anything is possible right?