Title:[1157] Whirlpool Galaxy in Canes Venatici Caption:The Whirlpool Galaxy, M51, NGC 5194/5195. This image was made by combining three CCD frames taken at the Kitt Peak 0.9-m 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 image 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 galaxy, made it necessary to use the drift scan technique. M51 (also known as Arp 85 and VV 1) comprises the large spiral galaxy NGC 5194 and its smaller, barred and more amorphous companion, M52, NGC 5195. Some features are better seen in a color picture: note, for example, how NGC 5195 takes on a reddish tinge due to the fact that it is behind the dust-filled arm connecting it to 5194. At a distance of more then 14 million light years behind the constellation Canes Venatici, the entire double system is over 65,000 light years across. Copyright: Credit:National Optical Astronomy Observatories/W. Schoening/N. Sharp

Title:[0037] Optical image of the interacting galaxy M51 Caption:M51 (NGC 5194), also known as the "Whirlpool Galaxy," is a spectacular face-on galaxy showing the classic grand design spiral structure with well-defined arms and central bulge. Its distance has been estimated at 7.5 to 9.6 Mpc (24 to 31 million light years). The field in this slide is ~15 x 15 arc minutes. M51 has a fainter companion, the lenticular galaxy NGC 5195 (to the north), with which it is interacting. This interaction has been numerically modeled in detail and explains the anomalous bridges and distortions. M51`s principal region of recent star formation is in the outer spiral arm, nearest to its companion galaxy. In fact, star formation here may have been triggered by the passage of the companion galaxy. Copyright:(c) Smithsonian Astrophysical Observatory 6 Credit:Courtesy of US Naval Observatory