The night sky of the pretelescopic era was a decidedly uncomplicated place. The heavens contained the fixed stars, the luminous band of the Milky Way, the moon and the five wanderers or planets, all known since before recorded history. Occasionally a brilliant comet swept across the sky; there were also shooting stars which appeared and disappeared in the blink of an eye. And very rarely, a brilliant ‘guest star’ would appear where no star had shone before and then slowly fade over the following months, disturbing the otherwise immutable starry vault.

Beyond this were a handful of cloudy spots in the sky, nature unknown, but like the stars they did not move and so could not be atmospheric phenomena. There was the hazy cloud of stars in the tail of Leo, named Coma Berenices, and the compressed grouping of tiny stars known as the Pleiades. There was a hazy patch of light in the Cassiopeia Milky Way which would one day be known as the Double Cluster. And finally there was the luminous patch in Cancer called the Praesepe.