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Physics & Astronomy Department

Astr112 Photography Projects, Fall 2007

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The Fireworks Galaxy (NGC 6946), Cedric Herman

NGC 6946

NGC 6946, or the Fireworks galaxy, was discovered by William Herschel in 1798. This beautiful, face on, spiral galaxy can be found in the constellation Cepheus. This particular object is classified as an intermediate spiral galaxy. An intermediate spiral galaxy is a galaxy that falls between a barred spiral galaxy and an unbarred one in classification. The dense spiral arms of this galaxy provide a nursery in which new stars can form. Toward the center there is a warm orange and yellow color from the older, less luminous stars. Larger galaxies like this one are formed from smaller dwarf galaxies and other interstellar matter that fall together with gravity. This particular galaxy is the location of an unusually high number of supernova explosions. In fact, during the 20th century alone there were six supernovae within this galaxy.

In this image, the spiral arms and the core are very pronounced and easy to see. The bright gold color in the core is due to the high number of older, cooler (therefore redder) stars near the core. Along the beautiful spiral arms it is possible to see pink HII regions and bright blue areas around newly formed, super luminous stars. It is also possible to see how luminous this galaxy is by comparison to the stars in the foreground stars. Because this galaxy lies nearly in the plane of the milky way, it is greatly affected by dust extinction and appears far less bright from our point of view than it normally would. I have estimated the angular size of this galaxy to be about 420 arc seconds. The distance to this galaxy is about 10 million lightyears. Using the small angle formula, I have estimated the linear size of this object to be about 20,000 lightyears.

References:
"NGC 6946." Astronomy Picture of the Day http://apod.gsfc.nasa.gov/apod/ap040410.html

"NGC 6946." National Optical Astronomy Observatory. http://www.noao.edu/outreach/aop/observers/n6946.html

"NGC 6946." Wikipedia. http://en.wikipedia.org/wiki/NGC_6946

Right Ascension (J2000) 20:34:48
Declination (J2000) +60:09:00
Filters used blue(B), green(V), red(R), and clear(C)
Exposure time per filter 300 seconds in CBVR
Date observed

October 18, 2007 (CBVR)