Hobby-Eberly Telescope

Astronomical reflecting telescope that began research in 1999 at the McDonald Observatory in the Davis Mountains of Texas. It has one of the largest mirrors of any telescope in the world. The Hobby-Eberly telescope can be rotated through 360° around a vertical axis, meaning that it can view a total of 70% of the sky visible from the observatory.

The light-gathering (primary) mirror consists of 91 curved hexagonal plates, each a metre or a few feet across, and together forming a surface 11.1 by 9.8 m (36.4 x 32.2 ft), which is part of a sphere, rather than the usual paraboloid. The plates are can be moved individually and are kept accurately positioned by pistons. The mirror is kept at a constant angle of 35° from the vertical, which eliminates the problem of distortion caused by the weight of a conventional mirror when it is rotated around a horizontal axis.

An object in the sky is tracked by moving a package of instruments about 13 metres (43 feet) from the primary mirror, following the moving point where the light from the object is focused. Cameras and a low-resolution spectroscope are mounted in this package. Light is also carried from it by optical fibres to a high- and a medium-resolution spectroscope. The telescope has been used to discover planets beyond our solar system, and to study the spectra of stars, supernovae, quasars and the nuclei of galaxies. It is operated by a consortium of US and German universities, and is named after the two principal donors, Lt-Governor William P Hobby Jr, of Texas and Robert E Eberly of Pennsylvania.