The Plate Vault

A century of celestial photography has left behind it an enormous number of exposed photographic plates at observatories around the world. Lick Observatory has one of the largest such collections, estimated at more than 150,000 direct images and spectrograms, made with every Lick instrument of the photographic era.

Four rooms in the "old photographic building" on Mount Hamilton make up the observatory's "plate vault." The photographs are stored in sub-collections, according to the telescope or instrument used to make them. Each sub-collection, which might itself comprise thousands of plates, is organized according to the "right ascension"—the east-west celestial coordinate—of a plate's center or of its target object. The picture above shows one wall of the room containing direct images taken with the 36-inch refractor, the 20-inch dual astrograph, the Willard lens, and a variety of smaller telescopes. At right are a few of the drawers holding Lick's huge collection of low-resolution spectra.

In the late 1980s, the last remnants of photographic observing disappeared at Lick in favor of electronic light detection and the plate vault ceased to grow. The plates nevertheless remain a valuable scientific resource.