42-Inch Reflecting Telescope

42-Inch Reflecting Telescope. . This 11-ton telescope, built by the Alvan Clark and Sons Telescope Manufacturing Company of Cambridgeport, Massachusetts, was installed at Lowell Observatory in 1909. It came with four secondary mirror combinations so that it could be operated at four different focal lengths. One secondary mirror was for the Newtonian focus, the shortest, giving a focal length of 18.3 feet (5.6 meters). Three other secondary mirrors were used with a modified classical Cassegrain focus of 53, 80, and 150 feet (16, 24, and 46 meters) respectively. Dr. Vesto Melvin Slipher used the 80 foot (24m) focus for spectroscopic studies for approximately 2 years. Earl C. Slipher used the 150 foot (46m) focus for Kodachrome pictures of the planets., From 1909 until 1950, staff astronomer Dr. C. O. Lampland was the principal observer with this telescope. During these years he made over 10,000 photographs of galaxies, diffuse nebulae, star clusters, and star fields. These images were used for studying any changes and motions within these objects and throughout the star fields. In 1922 Dr. Lampland and Dr. W. W. Coblentz, of the National Bureau of Standards, used this telescope to measure the surface temperatures of Mars, Venus and the other planets. After the discovery of Pluto on February 18, 1930, Dr. Lampland used this telescope to derive accurate positions for the determination of its orbit., Beginning in 1948, part of the observing time was allotted to the solar variations program, an investigation to determine the constancy of the light from solar-type stars. In 1969, a new 42-inch mirror made of low expansion glass was completed, and the decision was made to use a modern telescope mounting. The new telescope was placed at Lowell Observatory's dark sky site on Anderson Mesa 12 miles (19 km) southeast of Flagstaff. , This old telescope, although maintained in place in its dome, was not used much after 1970. In November 1999 it was removed from its original dome, and it was placed on display here in May 2001. . This historical marker is in Flagstaff in Coconino County Arizona