NGC 281 is an ionization nebula located 10,000 light-years away in the constellation Cassiopeia. Ionization nebulae are places where new stars are forming. They are composed mainly of hydrogen and have a reddish glow because of hot stars behind them which bring the hydrogen up to high energy levels. When the atoms fall down again from a certain energy level to the next lowest, they release the excess energy in the form of a photon emitted in the red section of the visible light spectrum.
NGC 281 is also known as the Pacman Nebula. The cloud of hydrogen gas is fairly round in shape. In the cloud there is an open star cluster, IC 1590. This bright star cluster makes up “Pacman’s eye”, and it is what is exciting the energy level of the hydrogen atoms. A little bit up and left of the “eye”, there is a dark spot. This is caused by dust which blocks the light. There is also a dark band just around and a little bit above “the mouth” which is also caused by dust blocking the light. As shown, the nebula spans about 50 light years.
Bennett, Jeffrey, Megan Donahue, Nicholas Schneider, and Mark Voit. The Cosmic Perspective. 6th ed. San Francisco: Addison-Wesley, 2010. 543-44.
Nemiroff, Robert and Jerry Bonnell. "Portrait of NGC 281" Astronomy Picture of the Day. 2008 December 10. Accessed 3 Dec. 2010. <http://apod.nasa.gov/apod/ap081210.html>
|Right Ascension (J2000)||00:53:29|
|Filters used||blue(B), green(V), red(R), and clear(C)|
|Exposure time per filter||5x60 seconds in C, 300 seconds in BVR|
October 25, 2010 (C)