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NGC 457: ET Cluster
Jessy Buiten

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The ET cluster is an open star cluster in which the stars are spread out. It has several other names such as the "Owl Cluster" or the more technical "NGC 457." The cluster is located in the constellation Cassiopeia and has over a hundred stars. Open star clusters are located in the disk of the galaxy. This differs from globular clusters which have hundreds of stars clumped together and are located in the halo. All of these stars from the ET Cluster were created around the same time from the same particles. Therefore, these stars are relatively the same age. All of the stars within the cluster are young. We can tell that the stars are younger because they are blue. Also, we know they are younger because the stars are still so close together. Open clusters do not have enough gravity (unlike the densely packed globular clusters) and are therefore unable to hold all of its stars together for long periods of time. The stars in the ET cluster are relatively near to each other which indicates how young the cluster is. According to the SEDS web site, NGC 457 is "rich; one of the best Cas (Cassiopeia) clusters."

This picture focuses on the cluster as well as the area above it. In the lower left corner are the stars which give NGC 475 the nicknames “ET Cluster” and "Owl Cluster."The two brightest stars look like the eyes of ET or the eyes of owls. The picture also shows how open the cluster is. The stars are relatively spread out. Many of them appear to be the same color except for the one in the middle left which appears to be red. This indicates that the star is cooler than the others. From my calculations and estimations of the picture, NGC 457 is 40 by 60 light years in size.

Bennett, Jeffrey, Megan Donahue, Nicholas Schneider, and Mark Voit. The Cosmic Perspective. 6th ed. San Francisco: Addison-Wesley, 2010. 511-512.

"The RASC's Finest N.G.C. Objects List." Students for the Exploration and Development of Space. Ed. Roy L. Bishop. Royal Astronomical Society of Canada (RASC), 6 Jan. 2005. Web. 6 Dec. 2010. <>.

Right Ascension (J2000) 1* 09' 00''
Declination (J2000) +58* 20' 00''
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 60 seconds VCR. 300 B
Date observed

October 25, 2010 BVRC



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