Telescopes I've Seen - McDonald Observatory

McDonald Observatory, University of Texas, Mt. Locke, Texas

Harlan Smith 2.7-meter dome

The largest telescope on Mt. Locke proper is the 2.7-meter (formerly 107-inch) Harlan J. Smith telescope, completed in 1968 with substantial support from NASA (thereby ensuring that a fair fraction of time would be available for planetary science). The site also includes the 2.1-meter Struve telescope, the 30- and 36-inch reflectors, and, on adjacent Mt. Fowlkes, the 9.2-meter (or 11-meter, but that's a religious war I have no stake in) Hobby*Eberly Telescope. Mt. Locke only looks like a mountain from the Fort Davis side to the south; the land to the north is higher so it's only a hill from that side. Among these, the 2.7-meter is the largest telescope I know of which uses a solid tube rather than an open framework to support the optical components.

The 107-inch has an unfortunate bit of notoriety in the astronomical community, as the victim of a handgun assault. Courtesy of at and a relay from Johan Booth, I found a news note in Sky and Telescope for April 1970 (page 23, "Gunfire in the Dome"). There is a footnote in Mark Pendergrast's book Mirror, Mirror: A History of the Human Love Affair with Reflection (Basic Books, 2003) giving the date as February 5, 1970. The S&T note mostly quotes information from director Harlan Smith, from IAU Circular 2209, that it happened on the night of 5/6 February 1970, and a 9mm pistol was involved for seven shots. Anyway, here's a picture looking down the tube showing the bullet holes in the primary. I'll decline to reveal who let me crawl into the tube to take this picture, though he hasn't worked at McDonald in some years. I show this one in class to make the same point that not seeing a shadow of the secondary mirror for in-focus star images does, but in a more striking way. The three blacked-out areas around bullet pits appear in the lower right part of the mirror in this view. A Web correspondent points out that there is a brief description of this episode in the epilogues to Big and Bright: A History of the McDonald Observatory by David Evans and J. Derral Mulholland (published by the Univ. of Texas Press in 1986):

Firearms are very common in Texas. Astronomer Brian Warner had his tongue only slightly in cheek when he remarked that "Jeff Davis County is about the size of Israel - and slightly better armed." The prophecy inherent in the aphorism came to pass. The full precipitating causes may never be known, but one February night in 1970 a McDonald Observatory employee (not a Texan, but an Ohioan newly hired from another observatory!) suffered a breakdown and carried a pistol to the observing floor of the 107-inch telescope. He fired a shot at his supervisor, and then unloaded the rest of the clip into the primary mirror. Happily, fused silica is more resilent than ordinary glass, and the big mirror did not break. The craters have been bored out and painted black to reduce any light-scattering effect, and the end result is simply a slight reduction in the efficiency of the telescope. It is now the equivalent of a 106-inch telescope. The incident made the national television news, with Walter Cronkite describing it before a projection showing the wrong telescope upside down.

Harlan Smith 107-inch telescope 107-inch mirror with bullet holes

Currently, the 36-, 82-, and 107-inch telescopes are listed as open for public viewing programs one or more nights a month. In the dark skies of West Texas, that must be really cool. You can explore the area starting with this satellite view from Google Maps.

Hobby-Eberly Telescope,

The 11-meter (usually asterisked, its design uses "only" about 9 meters at a time) HET represents an innovative way to get aperture for less money. Move the detector, not the mirror. A spherical primary mirror gives identically aberrated images in all directions, which can be corrected over a small field by local optics. The really bright idea (in my view) was pointing the telescope off zenith on a rotatable mount, giving access to much of the visible sky. A precision tracking mount lets cameras or spectrographs follow the moving target image for as much as an hour. These views include the dome (with tower putting an alignment laser at the mirror's center of curvature) and a view ofthe telescope (whch is hard to photograph because it fills the dome). The segmented mirror shows its curvature through the bent reflections of support struts that hold up the tracking and detector assembly.

Dome of Hobby-Eberly telescope Mirror and structure of Hobby-Eberly telescope

Telescope Collection

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