85 years ago this month Clyde Tombaugh used this large camera to discover Pluto.

On February 18, 1930, Clyde Tombaugh found what he had been assigned to search for – Planet X. He found the world that soon became known as Pluto.

The instrument he used, shown above, was a refractor telescope of sorts, designed specifically for the Pluto search. It focused its light onto large photographic glass plates. Tombaugh would take images of selected fields each night, looking for objects that moved from night to night.

The Astrograph is housed in this building, now an historic site at the Lowell Observatory on Mars Hill in Flagstaff, Arizona and open daily for tours. The Astrograph is on the upper floor of the wooden Observatory; the lower floor contained the darkroom where Tombaugh developed the plates.

To search for Pluto, Tombaugh mounted the fragile glass plates in what is called a blink comparator. You can see it at right in the image above, of the interior of the old Library building at Lowell, now used as a museum and as part of Lowell’s excellent Visitor Centre program.

Using the comparator, Tombaugh would blink the images from two plates back and forth. Stars would appear to stay put, but any moving objects in orbit around the Sun would jump back and forth as they shifted position from one night to the next.

On February 18, he found an object that moved as expected, on plates he had taken the month before, and announced to his superiors that he had found the long-sought for Planet X, first hypothesized by the Observatory’s founder, Percival Lowell. It was another month before the discovery was made official and announced to the world.

Lowell is entombed in the Mausoleum on the Observatory grounds, and next door to the other telescope for which he is most famous.

This historic wooden dome contains the 24-inch Clark Refractor that Lowell used to “discover” the canals of Mars, to bolster his theories about a dying race on Mars husbanding the last remnants of water on a drying planet.

The ideas of intelligent life on Mars popularized by Lowell continued to influence science into the space age and continue to influence the public even today.

But it was Lowell’s other fascination with Planet X that led to the discovery of what was called the ninth planet, now called a dwarf planet.

Pluto is the destination this year (on July 14) for the NASA New Horizon space probe, in this Year of Pluto … and Year of the Dwarf Planet, with the arrival next month of NASA’s Dawn probe at Ceres, the largest object in the classic asteroid belt, and also classified as a dwarf planet.

I shot these images of Lowell’s historic sites on February 8, 2015 as part of a visit to the Observatory to deliver a club and public talk.

– Alan, February 17, 2015 / © 2015 Alan Dyer / www.amazingsky.com