In the mid-19th century, irregularities in the orbit of the planet Neptune led astronomers to suspect that there may be a ninth planet. At first, the inaccurate orbital data made it difficult to identify where exactly to look. Later on, time lapsed exposures were compared using the naked eye, a time-consuming process.
The development of the blink comparator at Carl Zeiss in 1904 was a major turning point. It showed in rapid succession two images of the same region of the sky taken at different times. Their change in position makes celestial bodies stand out in the foreground, thus simplifying the search considerably. At the Lowell Observatory on February 18, 1930, young research assistant Clyde Tombaugh used this apparatus to compare two images on photographic plates that he had taken on January 23 and 29. Lo and behold, in the space between Taurus and Gemini he found a tiny object: Pluto.
Pluto is no longer classified as a planet. Because additional bodies were discovered at the edges of our solar system, the International Astronomical Union decided in August 2006 to place it in the newly defined class of dwarf planets. After the discovery of its somewhat larger neighbor Eris in 2005, Pluto is only number two in this category.
February 9, 2010