NGC 457とは 意味・読み方・使い方

NGC 457 (also known as the Owl Cluster, the ET Cluster, or Caldwell 13) is an open star cluster in the constellation Cassiopeia. It was discovered by Friedrich Wilhelm Herschel in 1787. and lies over 7,900 light years away from the Sun. It has an estimated age of 21 million years. The cluster is sometimes referred by amateur astronomers as the Owl Cluster, Kachina Doll Cluster, or the ET Cluster, due to its resemblance to the movie character. Two bright stars, magnitude 5 Phi-1 Cassiopeiae and magnitude 7 Phi-2 Cassiopeiae can be imagined as eyes. The cluster features a rich field of about 150 stars of magnitudes 12-15.