The Hale 200″ telescope on Mount Palomar.

This was the largest telescope in the world from 1948 until 1976, and its images illustrated most of the astronomy books when my generation was growing up.

The optical tube employs a Serrurier Truss, which is designed to allow flexure, yet keeps the optical components precisely aligned. The scope swings in declination in a yoke-type mount, modified at its upper end into a horseshoe shape which allows pointing right up to the north celestial pole.

As the telescope is still an active research instrument in use every clear night, the observatory is air-conditioned and visitors are kept behind the glass windows of the viewing room, hence the reflections visible in the image. Photographed in July 2014 by the author.

The dome housing the 200″

– is almost as impressive as the telescope. The author appears in the foreground.