Photo: The Pluto Discovery Telescope

By Kevin Schindler

Percival Lowell postulated the existence of a planet beyond Neptune and began to search for it in 1905.

He spent his remaining 11 years in a mathematical and observational search for the elusive “trans-Neptunian” planet. Upon Lowell’s death in 1916, the search was suspended while the Observatory went through protracted legal wrangling about Lowell’s estate. In 1927, once the estate was finally settled, Percival’s brother — Harvard University President A. Lawrence Lowell — provided the funds needed to construct the telescope and dome you can still see every day here on guided tours.

The Pluto Discovery Plates, courtesy Lowell Observatory Archives

The glass plates Tombaugh painstakingly compared in order to locate Pluto. | Lowell Observatory Archives

The new telescope was completed in 1929, and the Observatory hired a farm boy from Kansas named Clyde Tombaugh, who had impressed director V. M. Slipher with some unsolicited sketches, to help renew the search.

The process was laborious: Tombaugh would photograph the same part of sky several days apart and use a Zeiss Blink Comparator to detect the motion of a nearby planet against the more distant “fixed” stars. Once Tombaugh got going toward the end of 1929, the discovery came remarkably fast: on February 18, 1930, he detected the distant planet on plates taken on the 23rd and 29th of January.

The discovery was announced March 13, 1930. On the evening of March 12, director V.M. Slipher sent a telegram to the Harvard College Observatory. The telegram’s message was used to create Harvard College Observatory Announcement Card 108, which officially announced the new planet’s discovery and was released on the 13th. Slipher wrote a more detailed account of the discovery and printed it as a Lowell Observatory Observation Circular, also releasing it on the 13th. Astronomer Carl Lampland was busy as well on this day. On behalf of the Observatory, he presented the Lowell Prize to the top mathematics student at Arizona State Teacher’s College at Flagstaff (today known as Northern Arizona University). The ceremony was in front of a 500-person audience in Ashurst Hall. As part of his speech, Lampland made the first public announcement of the new planet’s discovery. Unfortunately, few, if any, of the audience members heard this important message, since the soft-spoken Lampland could not be heard in the echo-filled, uncarpeted room. The announcement date was significant, for it had been March 13, 1781 that William Herschel discovered Uranus. Also, March 13, 1930 would have been Percival Lowell’s 75th birthday, a fitting tribute to the man whose inspiration led to the discovery of this new planet by Clyde Tombaugh.

Check Out #TeamPluto!

90 years ago, Pluto was discovered by scientists at Lowell Observatory. In 2006, Pluto was reclassified as a dwarf planet. How did this happen? This Discovery documentary follows YouTube star and TV host Nick Uhas and a team of esteemed scientists on the quest to understand the fierce fascination with Pluto’s planetary standing. Watch below: