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Want to discover Planet X? You'll need these three tools

Courtesy Lowell Observatory

Clyde Tombaugh and the blink comparator

Clyde Tombaugh compared photographic plates taken in Percival Lowell's designated Planet X search area using the blink comparator. One year and two days after observations began, Tombaugh spotted Pluto.  

Lowell Observatory’s intermittent 25-year search for a trans-Neptunian planet incorporated a variety of instruments before finally netting Pluto. Some were highly specialized commercial devices, while others were modified mechanisms designed and built by Lowell staff.

Here are three of the most critical:

Zeiss Blink Comparator

During Percival Lowell’s early search for Planet X, he compared pairs of photographic glass plates of the sky by overlapping the two and then examining them with a magnifying lens. This proved inefficient and inaccurate; in 1911, at the suggestion of staff astronomer Carl Lampland, Lowell solved the problem by purchasing a stereo blink comparator.

Built by the noted Carl Zeiss optical firm of Jena, Germany, this specialized microscope holds the plates side by side. A mechanical shutter allows the observer to alternately see first one image and then the other while looking through a microscope eyepiece.

This instrument was originally designed to hold 6-by-7-inch plates, but Lowell staff found 14-by-17-inch plates to be the best size for the Planet X search. Lampland accordingly modified the apparatus by designing slip frames allowing for a quarter of the large plates to be examined at a time.

Several weeks ago, Lowell Observatory sent the blink to the Smithsonian National Air and Space Museum, where it will be on display for the next three years

Take a look, could you have discovered Pluto on the blink comparator?

The Millionaire machine

During his search for Planet X, Lowell also employed a number of “computers.” These were people hired to make laborious mathematical calculations, in this case to determine the location of the alleged planet. To supplement these efforts, Lowell bought a Millionaire calculating machine in 1914.

The Millionaire was a motor-driven device developed by Swiss engineer Otto Steiger and modified for production by Hans Egli of Germany. The first one sold in 1893. Over the next 40 years, some 5,000 were produced. It was superior to other calculating machines of the time because of its rapid speed of operation, allowing users to make eight-digit calculations in less than ten seconds.

These machines were ideal for applications requiring frequent multiplication and division, particularly in industries such as insurance, mining, and railways. They were the most effective calculating devices until the arrival of fully automatic rotary calculators in the 1930s.

Lowell’s Millionaire is displayed in the Putnam Collection Center at Lowell Observatory.

Pluto Telescope

Thanks to a $10,000 donation from Percival Lowell’s brother, Abbott Lawrence Lowell, longtime president of Harvard University, Lowell Observatory built a 13-inch astrograph specifically to search for Planet X.

Instrument maker and jack-of-all-trades Stanley Sykes worked with pattern maker Edward Mills to design and build patterns made out of local ponderosa pine. They sent the patterns to foundries in Albuquerque, El Paso, and Los Angeles, where they were cast into iron parts to build the telescope and portions of the dome.

For the dome, Sykes used the same design as the one his brother Godfrey created to build the 24-inch Clark dome. Work on the mount and dome began in early 1928, and the lens, designed by Carl Lundin of Alvan Clark & Sons — the same company that built the 24-inch refractor—arrived on February 11, 1929. Staff members captured the first photographic plates on February 16. One year and two days later, Clyde Tombaugh vindicated the entire effort when he discovered Pluto.


Kevin Schindler is a science writer at Lowell Observatory in Flagstaff, Arizona.
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