Whirpool Galaxy (M51), 31 March 1889.

UNITED KINGDOM - JUNE 09: Photograph of the Whirlpool galaxy (M51) taken on 31 March 1889 with an exposure of 3.5 hours. Dr Isaac Roberts, an amateur astronomer and pioneer astrophotography, took this image using a 20 inch aperture reflecting telescope. Made by Howard Grubb of Dublin, the telescope was first installed at his home near Liverpool, but later in 1890 he moved it to the less smoky skies of Crowborough, Sussex. In 1887, Roberts was invited to attend the first international conference in Paris on celestial photography. Here astronomers decided to embark on the, 'Carte du Ciel' an ambitious project to photograph the whole sky in unprecedented detail. (Photo by SSPL/Getty Images)