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Astronomical Observatory: Cool Images

Images: Whirlpool Galaxy

Whirlpool Galaxy

This is an image of the central region of the Whirlpool galaxy. It was discovered in 1773 by the French comet hunter, Charles Messier, who described it as a "very faint nebula". (He listed it in his catalog of nebulae, from which comes its alternative name, M51.) He saw what we can see by eye in our own telescope, the relatively bright (magnitude 8.4) fuzzy core of the galaxy. The much fainter spiral structure was discovered by Lord Rosse in 1845, using his giant 6-foot reflector telescope, and was the first spiral nebula known.

A consensus among astronomers was reached in the 1920s that spiral nebulae are in fact galaxies of hundreds of billions of stars similar to our own Milky Way. Most stars lie in a disk (seen in this instance face on) making circular orbits around the galactic core. The spiral structure is a wave propagating through the disk that is particularly prominent due to the narrow dust lanes and the luminous, short-lived stars that outline the arms. The low intensity of the arms despite the high intensity of its stellar constituents is a consequence of the vast empty spaces between stars in galaxies.

Processing: This image was made by Phil Ammar in Astr384 in Spring 2004 (follow link for processing details) using the Calvin-Rehoboth robotic telescope with 52 exposures and 4.3 hours total exposure time. This image is an improvement over a monochrome image made by Phil in March 2002 under Grand Rapids sky conditions with 226 exposures and 1.2 hours total exposure time.

Orientation and scale: North is up and East is to the left. The image is 7.2 by 5.2 arcminutes. The galaxy core has celestial coordinates 13h29m53s, +47d11'48" (epoch 2000), which is 3.6 degrees southwest of Alkaid, the star at the end of the handle of the Big Dipper.

The disk of the Whirlpool is some 40,000 light years across and approximately 35 million light years away from Earth.

Content updated 9/7/05.





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