Telescopes I've Seen - U.S. Naval Observatory

United States Naval Observatory, Washington, D.C. and Flagstaff, Arizona

USNO Flagstaff Station

The US Naval Observatory has as a primary mission the support of time and reference frames as needed by Department of Defense activities. This also makes it a world center for precision astrometry and basic stellar data. The current location, to which the "Depot of Charts and Instruments" was relocated from aptly-named Foggy Bottem, features the classic 12- and 26-inch refractors, the latter being the instrument used by Asaph Hall to discover Phobos and Deimos. A USGS image (formerly from the Terraserver site) is shown below. The 12-inch refractor is in the central building, while the 26-inch instrument is in the separate dome to its northest (upper left).

USNO 26-inch refractor USNO 12-inch refractor
USGS aerial photo of USNO Washington site

Fleeing the light pollution (and typically Eastern weather, which is to say bad) of central Washington, the USNO also established a field station just west of Flagstaff, Arizona (visible from the proper lanes of I-40 as one drives by). The entrance is graced by some of the highest-altitude anchors in the country. The major instruments are 1-m and 1.5-m (shown at top) reflectors. The 1.5-m is interesting in using, not a Cassegrain optical system, but a folded prime focus arrangement with a flat secondary mirror. For controlling astrometric distortions, such a setup is valuable because there are fewer terms in the distortion that can be introduced by slight misalignment of optical elements than in a Cassegrain system, or a Ritchey-Chretien (of which the USNO 1m was one of the earliest examples). The Navy's Prototype Optical Interferometer (NPOI) at nearby Anderson Mesa is also managed by the Flagstaff astronomers.

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