NGC 281 is an emission nebula near Cassiopeia. An emission nebula is a large cloud of gas and dust in space. Emission nebulae glow because the heat of the nearby stars ionizes the gas. We see the red when the electrons in the hydrogen atoms drop from an energy level of three to two. It is often the origin of thousands of stars. In fact, this nebula is the birthplace of the open cluster, IC 1590. It was discovered in 1883 by E. E. Barnard. NGC 281 is approximately 10,000 light-years away and the image above is about 50 light-years across.
In this image of NGC 281, we see a predominately red color. A red color refers to an HII region. An HII region is composed of hydrogen gas. The hydrogen is ionized by hot stars and thus emits a red hue. The stars in the center are blue, which means that, if they are Main Sequence stars, they are high mass. This also means that these stars have a short lifespan, and thus we are seeing them when they are young. These stars seem to have been born out of this nebula, when a dense region of gas collapsed. We can also see some dark clouds at the foreground of the image. These are dense clouds of dust known as dark nebulae that block visible light of the objects behind it. NGC 281 is also known as the "Pacman Nebula." Often, this nebula will resemble the Pacman icon, with its eye and large mouth.
Bennett, Jeffrey, Megan Donahue, Nicholas Schneider, and Mark Voit. The Cosmic Perspective. 6th ed. San Francisco: Addison-Wesley, 2010. 595.
"NGC 281: Cluster, clouds, and globules." NASA Image of the Day Gallery. Retrieved December 4, 2010, <http://www.nasa.gov/multimedia/imagegallery/image_feature_31.html>.
Lodriguss, Jerry. In Catching the light. Retrieved December 4, 2010 <http://www.astropix.com/HTML/SHOW_DIG/NGC281_Pac_Man_Nebula.HTM>.
|Right Ascension (J2000)||00:52:48|
|Filters used||blue(B), green(V), red(R), and clear(C)|
|Exposure time per filter||300 seconds|
October 25, 2010