The Whirlpool Galaxy in the constellation Canes Venatici, a face-on, grand-design
spiral galaxy of type Sc, was the first in which spiral structure was clearly seen
(by Lord Rosse). It forms an interacting pair of
galaxies with its neighbor, M51B (NGC 5195). This
gorgeous image was obtained with the Kitt Peak 4-meter Mayall telescope, in 1975.
This image of M51 (NGC 5194) and M51B (NGC 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 M51B (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