A Globular Cluster and A Comet

Figure Obtained from: Astronomy Picture of the Day

            The picture that was posted on Astronomy Picture of the day on February 4^th 2012 is a picture of a comet as well as a globular cluster. The comet that is shown in the picture is called Comet Garradd and it is slowly moving through the constellation Hercules. Comets are characterized by the tails that they emit when they are close to a star. The ice on the comet vaporizes and forms and ion tail and the other tail are a dust tail. The dust tail is caused when the ice melts and there is nothing to hold the dust in a clump anymore. The tails of the comets will always point away from the star and the curved tail is the dust tail.  The reason that the tails point away from the star is because they are pushed out by the pressure of the starlight. The other interesting aspect of this picture is the cluster of stars that can be observed to the left of the comet. This cluster of stars is known as a globular cluster. This means that the stars in the clusters are horizontal branch stars, red giants, and lower mass main sequence stars. A globular cluster will have an absence of high mass main sequence stars because of the life time of these stars. Globular clusters are clusters of stars that are gravitationally bounded to each other. This means that there are very few stars that can escape the cluster.  Globular clusters are also thought to be older clusters and this can be seen because of the absence of the high mass main sequence stars. Larger main sequence stars burn bright a die young and therefore, these stars would have already burnt through the main sequence and would have turned off the main sequence to become a giant and finish the post main sequence stellar evolution. This picture is interesting because it allows one to look at two aspects of the universe.