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McDonald Observatory Telescopes

Written by E. Dan Klepper.

The McDonald Observatory has nine primary research telescopes with varying capabilities and purposes. Here’s a look at some of facility’s powerful tools.

Otto Struve Telescope

Completed in 1938, the Otto Struve telescope served as the mountain’s only telescope for almost two decades. During that time it also provided room and board for the telescope’s astronomers, a service now provided by the Astronomer’s Lodge and separate housing. With a mirror weighing 4,200 pounds and an 82-inch diameter, the Struve was the second largest telescope in the world upon its completion. Despite its old age, the granddaddy of the observatory continues to provide opportunities for important research thanks to instrument updates. The telescope’s namesake was the observatory’s first director, who held the position from 1932 to 1947.

Harlan J. Smith Telescope

The 160-ton Harlan J. Smith offers two different configurations for observing distant planets and other space objects. The 107-inch mirror and corresponding lens can direct light to attached instruments or to independent instruments stationed in a room one floor below the telescope. Although called the 107-inch (a reference to the diameter of its mirror) the telescope actually has a light-gathering capacity of 106 inches. In the 1970s, a disturbed employee shot the mirror seven times with a 9-millimeter pistol at point-blank range, causing small impact craters that damaged a tiny amount of the mirror and slightly reducing its efficiency. Smith directed the observatory from 1963 to 1989 and spearheaded the telescope’s construction in the mid-1960s.

Hobby-Eberly Telescope

This beautiful behemoth, completed in 1997, supports a mirror with a 36-foot diameter comprised of 91 hexagonal segments (each one individually controlled) and a 160,000-pound telescope. Unlike the other telescopes which are scheduled for research times by astronomers according to specific dates, the Hobby is trained on objects each night according to real-time factors like weather and moon phases, providing opportunities to explore sudden events including exploding stars.

The 36-inch

A popular telescope for the observatory’s special viewing night programs, the 36-inch served to meter the brightness of stars for many years after it was completed in 1956. The instrument’s manufacturers designed its mirror for maximum light-gathering capacity, providing bright, rather than detailed, observations.,

The 30-inch

The 30-inch, the smallest research telescope of the collection, utilizes half of the glass cut from the center of the Harlan J. Smith telescope mirror. The 30-inch has a wide-angle field of view (bigger than the area of sky taken up by the full moon), making this telescope perfect for general night sky survey projects.

The Laser Ranging Telescope

Travel time and distances are the main research tasks of the Laser Ranging Telescope, a small telescopic device utilizing the other half of the glass cut from the Smith mirror. Laser beams are fired at retro-reflectors on specially equipped satellites and panels deployed by Apollo astronauts on the surface of the moon, and the returning light is reflected back into the telescope. The procedure actually reveals details about complex concepts like continental drift and lunar motion.


Designed to assist school students in observing the cosmos, the observatory’s MONET (Monitoring Network of Telescopes) is operated remotely from classrooms in Germany and Texas, among other places. The McDonald MONET is companion to a second telescope located at the South African Astronomical Observatory and, together, the two provide a complete view of the night sky.

The Boston University Telescope

The 16-inch Boston University telescope has been used to study the atmospheric environments of planets and moons, including our own. During one particular research project, the Boston explored the dense atmosphere of Jupiter’s volcanic moon known as Io.

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