NGC 246, also known as the Skull Nebula, is a planetary nebula in the constellation Cetus. Planetary nebulas are made of material that a star has thrown off after it runs out of hydrogen fuel to burn. The main star in NGC 246 is the white dwarf HIP 3678.The Skull Nebula is about 475 parsec (pc) (about 1600 light years) away. It was discovered in 1785 by William Herschel and is moving through the universe at about 80 km/sec.
In this particular image you can clearly see the green airy looking stuff, which is the aforementioned material that was thrown off by the star when it ran out of hydrogen fuel to burn. This stuff is green because of the material it is composed of, which in this case is oxygen. The brightest star in this nebula, white dwarf HIP 3678, is the source of the material and is almost dead center of the green and appears to be blue. This blue color indicates that this star is extremely hot. There are four other relatively bright stars in the picture, but none of these are as bright as the one in the middle of the nebula and are also foreground and background stars, and have nothing to do with the nebula itself. The darker outer ring of the nebula is thought to be from the action of shock waves, which are caused by objects moving at supersonic velocities. The distance to this object is estimated to be 1600 light years; we find a maximum angular size of 260.7 arcseconds, which corresponds to a linear size of about 2 light years.
Darling, David. "Skull Nebula (NGC 246)." <http://www.daviddarling.info/encyclopedia/S/Skull_Nebula.html>.
Bennett, Jeffrey, Megan Donahue, Nicholas Schneider, and Mark Voit. The Essential Cosmic Perspective. 6thth ed. Boston: Addison-Wedley, 2012. Print.
Centre de Donnees astronomiques de Strasbourg. SIMBAD. <http://cds.u-strasbg.fr/>.
|Right Ascension (J2000)||00:47:03|
|Filters used||B (Blue), C (Clear), R (Red), V (Green)|
|Exposure time per filter||B, V, C, and R (60s x 5)|
|Date observed||October 14, 2011|