Aluminium Spectroscopic Plate from the Sloan Digital Sky Survey (SDSS)

Sloan Digital Sky Survey spectra or ‘plug’ plate, Used in astronomical sky survey to select sky areas of interest for spectroscopy. USA, c.2000

The Sloan Digital Sky Survey is one of the largest astronomical surveys ever completed. Between 2000 and 2008 it created a 3D map of over a million stars and galaxies, covering a quarter of the night sky. This plate is one of about 4000 custom-built to fit the survey telescope at Apache Point Observatory in New Mexico. Each plate carries a unique pattern of 640 holes, used to select hundreds of stars and galaxies for each exposure. The circled guide stars marked on the plate help astronomers align it to the sky.