Clyde Tombaugh- Famous Astronomer of the 20th Century

Clyde Tombaugh--one of the greatest visual astronomers of all time--was the discoverer of the dwarf planet Pluto. This one and only discovery of a planet during the last century (dwarf or otherwise) took place on February 18th, 1930. The announcement was made from the Lowell Observatory located just outside Flagstaff, Arizona.

How Clyde Tombaugh became the discoverer of this famed object is the stuff of legend. Born on a Kansas farm, the young Tombaugh was already a skilled amateur astronomer prior to being hired by the Lowell Observatory to conduct a search for a suspected object beyond the orbit of Neptune. Using a telescope, a wide-angle camera and black and white photographic plates Tombaugh took hundreds of images near the path in the sky where a suspected planet might be found. 

After producing identical sets of photographic plates of the sky taken days apart, Tombaugh used an optical-mechanical device called a Blink Comparator to visually compare each plate to tease out any candidates. When he shifted views between his two images, any moving object, such as a planet, would appear to jump from one position to another, while the more distant objects such as stars, would appear stationary. After searching through countless star fields and enduring many false alarms over a period of over a year, an object was finally discovered that had every indication of being a distant object beyond the orbit of Neptune. After careful confirmation by other astronomers, the 9th planet in the Solar System, which would be dubbed Pluto, was announced to the world. 

Beginning in the 1990s, Pluto’s status as a planet was beginning to be questioned following the discovery of other objects of similar size located in a region beyond the orbit of Neptune known as the Kuiper Belt. This led the International Astronomical Union (IAU) to formally define the term "planet"—excluding Pluto and reclassifying it as a dwarf planet (minor planet designation: 134340 Pluto) in 2006. Subsequent observations have shown that Pluto has five known moons: Charon , Styx, Nix, Kerberos, and Hydra. The New Horizons spacecraft performed a fly by of Pluto on July 14, 2015, becoming the first and, to date, only spacecraft to do so. 

Clyde Tombaugh died in 1997. Tombaugh Regio, the largest, bright surface feature on the surface of Pluto is named in his honor.