This image of M51 (NGC 5194/5195), was made by combining three CCD frames, taken at the Kitt Peak 0.9m telescope in 1991. By using different filters in front of the monochrome detector, corresponding approximately to the primary colors red, green and blue, it is possible to recreate a true color picture. Each image was processed to correct for detector sensitivity variations and to remove incorrect regions caused by manufacturing defects and by the arrival of cosmic rays at the telescope.

This picture was made using the `drift scan' technique, in which the telescope is held fixed, not tracking against the Earth's rotation in the usual manner. As the sky passes across the detector, each row of the array is `clocked' along to the next row in step with the apparent motion of the astronomical image. This makes it possible to take a picture of an arbitrarily long strip of the sky, and specialized telescopes exist solely to take advantage of the simplicity of a fixed, non-tracking mounting. The large size of the M51 system, famous as the first clearly recognized spiral nebula, made it necessary to use the drift scan technique. Orientation: N to the left, E down.

The spiral arms are perhaps the most perfect `textbook' example in any nearby galaxy, and their very perfection points to the presence of a long-lasting confining mechanism. This may be provided by the tidal pull of NGC~5195, whose gravitational effects can generate the necessary spiral density waves. This pattern also shows up in radio emission, suggesting that the magnetic fields in the Whirlpool are also compressed by the density wave. The innermost core of M51 (NGC 5194) contains a bright ultraviolet source, as well as one of the brightest known compact radio sources. Due to recent star formation and the resultant dominance by young, hot, bright stars of spectral types O and B, M51 is considerably brighter than our own Galaxy.
Credit: Todd Boroson/AURA/NOAO/NSF

This image of M51 was taken with the NOAO Mosaic CCD camera on the National Science Foundation's 0.9-meter telescope located at Kitt Peak National Observatory near Tucson, AZ. The color image was generated by combining images taken through five filters (B, V, R, I and Hydrogen-alpha). The image shown above is only one tenth of the entire field of view of Mosaic on the 0.9-meter telescope.

Hot, massive stars which recently formed give the main galaxy M51 (NGC 5194) its bluish color. The reddish areas are diffuse nebulae, mainly consisting of hydrogen, in the galaxy in which new stars are rapidly forming.
Credit: Travis Rector, Monica Ramirez/AURA/NOAO/NSF

Last Modification: July 7, 1999