Originally printed in the Feb. 26, 2003 edition of the Illinois Valley News
Before the invention of telescopes, astronomers were aware of five objects in space which did not move the same way as stars. They called these objects planets, from the Greek word “piano” which means wandering. Mercury, Venus, Mars, Jupiter, and Saturn were all named for Roman gods. The next planet, Uranus, named for a Greek god, was discovered by a careful telescopic examination of the sky. Neptune, named for a Roman god, was discovered by a brief telescopic examination after mathematics had predicted the location. The last planet, Pluto, was discovered using careful photography and meticulous comparison of photographs taken of the same area over a period of time.
On Feb. 25, 1930, Clyde Tombaugh, a relatively unknown astronomer, observed proof that a new planet was in space beyond Neptune. Tombaugh, born Feb. 4, 1906 in Illinois, received very little academic training in astronomy. He had made observations of planets from his home using homemade telescopes. In 1928 he made sketches of Jupiter and Saturn and sent them to the Lowell Observatory near Flagstaff, Arizona. He was offered a job to join the staff at the observatory and assigned to make photographs of certain sections of the sky. Photographs were made on Jan. 23” and 29” in 1930 of the same section of space. One speck of light appeared to be shifting in relation to the other stars. Another set of photos on Feb. 18” confirmed the uniform movement. To make final proof, another set was taken on Feb. 25, 1930 which showed the speck moving exactly as a planet beyond Neptune should move. This finding was publicly announced by the observatory on March 13 and the name Pluto was eventually chosen. Pluto was the Roman god of the underworld, the planet Pluto is so far from the sun that it is in perpetual darkness.
Clyde Tombaugh continued working for the Lowell Observatory until 1945 and photographed about 65% of the night sky. He discovered more than a hundred asteroids, a comet, several star clusters, and a nova in 1932. He began working at the White Sands Proving Grounds in 1946, developing tracking telescopes for the USA space program. After about ten years Tombaugh joined the staff at New Mexico State University and developed an astronomy program there. He retired in 1973 and died in 1997 due to heart congestion.
The planet Pluto has been in the news recently. Some astronomers want to classify it as a comet rather than a planet. It is an unusual planet with a very elliptical orbit which makes it come closer to the sun than Neptune for part of its orbit. Studies of its gravitational pull indicate it has a very light density. Some books refer to Pluto as a “dirty snowball”. However, more recently observations from the Hubble Telescope show it to be about 70% rock and 30% water ice with a little frozen methane and maybe carbon monoxide.
Pluto also has its own satellite, named Charon . Charon was discovered in 1978 by Jim Christy and is named for the mythological water boatman who ferried the dead across the River Styx into the underworld. Charon is very large, for a satellite, so Pluto and Charon actually revolve around each other with the same side on each always facing the other. Whether Pluto is officially called a planet or a comet will not change its orbit and its position in space. Pluto will continue to be a mystery until a space probe is able to make a close visit and send back more detailed information.