The image above is a planetary nebula known as both the Clownface Nebula and the Eskimo Nebula. A planetary nebula is a luminous shell of gas ejected from an old, low-mass star that has run out of hydrogen fuel to burn; the gas is illuminated by the remaining ultraviolet light from the star, creating the vibrant colors that we see (Comins and Kauffman III 304). Clownface, in particular, was discovered on January 17, 1787 by William Herschel. It is found in the constellation Gemini, but its distance is not well known, though some estimates put it at around 3,000 lightyears away from the Earth ("NGC 2392"; Netzel).
Clownface's actual star is seen in the center of the nebula, about as bright as the surrounding stars in this particular image. We know that because this nebula is both planetary and bipolar that the star is "in its final death throes" and joins the other 20,000 to 100,000 other planetary nebula in the Milky Way (Comins and Kauffman III 305-306). Unique to Clownface is a distinctly blue central star, followed by expanding shells of green. The color of the star itself demonstrates the ultraviolet light we would expect in a planetary nebula and also shows that the star is far hotter than the shells, for blue is one of the "hottest colors" our eyes can perceive (the blue is seen better in the original file at this link). Another distinction is in the expanding green shells. Because the green is an emission line, we can use Kirchhoff's Laws to deduce that the shells are composed of oxygen. Though the distance to the Clownface Nebula is not totally known, it is estimated that the distance is about 3,000 lightyears ("NGC 2392"; Netzel). The maximum angular size is 47.48 arcseconds, which corresponds to an approximate linear size of .7 lightyears. The Clownface Nebula is an excellent example of a basic planetary nebula, and it is one of the most glorious sights in our galaxy.
Comins, Neil, and Kaufmann III William. Discovering the Universe. 5th ed. New York, NY: W.H. Freeman and Company, 2000. 301-307. Print.
Frommert, Hartmut. "NGC 2392." Students for the Exploration and Development of Space. Students for the Exploration and Development of Space, n.d. Web. 12 Apr 2011. http://spider.seds.org/spider/Misc/n2392.html
Netzel, Garrison. "NGC 2392." Macalester College. Macalester College, 7 May 2001. Web. 12 Apr 2011. <http://www.macalester.edu/astronomy/research/phys20/P20-2001/GN/clownface.htm>.
|Right Ascension (J2000)||7:29:12|
|Filters used||B (Blue), C (Clear), R (Red), V (Green)|
|Exposure time per filter||B, V, R, and C (60s x 5)|
|Date observed||March 24, 2011 EDT|