Gaithersburg Latitude Observatory

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The Gaithersburg Latitude Observatory, in Gaithersburg, Maryland is one of the system of six International Latitude Observatories and (as of 2004) the only National Historic Landmark in the City of Gaithersburg. The building is in the National Register of Historic Places. The GLO was constructed by Edwin Smith, Chief of the Instrument Division of the U.S. Coast and Geodetic Survey.

The Gaithersburg Latitude Obseratory was one of six observatories tracking the degree of “wobble” occurring on the earth’s north-south axis. The Observatory — along with observatories in Cincinnati, Ohio; Ukiah, California; Mizusawa, Japan; Charjui in Russian Turkestan; and Carloforte, Sardina, Italy — performed close in concert carrying out a program of star study designed to investigate and calculate the earth “wobble” or latitude variation.

On the grounds of the Gaithersburg Latitude Obseratory stands a plaque that reads:

“This small framed structure played a key role in the scientific investigation of the Earth’s rotation. In 1898, the International Geodetic Association established a network of observatories to measure the wobble of the plant on its axis by plotting the locations of specific stars. This hilltop in Gaithersburg was chosen together with sites in California, Italy, Japan, and the Soviet Union. All five lay along the same latitude (39° 8’ N). The American Stations were supervised by the U.S. Coast and Geodetic Survey. The observatory’s roof was designed to part in the middle on two sets of tracks to expose the reflecting telescope inside to the night sky. Its slatted exterior walls stabilize the inside air to limit the effects of the temperatures on the accuracy of the telescope. The building’s white paint minimizes heat retention that creates air turbulence around the telescope at night, distorting the stars. Knowledge gained from the observations recorded here nightly until 1982 assisted scientists in the study of the Earth’s geophysical make-up and aided spacecraft orbiting the planer and navigating the universe.”

According to the Special Publication No. 27 (dated 1915, of the Latitude Observations with Photographic Zenith Tube at Gaithersburg MD, borrowed from the Johns Hopkins Library system), a second portion of the observatory was constructed to house the Photographic Zenith Tube. The observers used the Photographic Zenith Tube to capture picture data using the Zenith telescope as a guide of alignment and star track. Unfortunately, time has not been very kind to this addition of the Gaithersburg Latitude Obseratory as it no longer stands at the site.