Collinder 8

The Pacman Nebula, NGC 281, is a broad emission nebula some forty light years across, in the constellation of Cassiopeia. The nebula, which lies a little less than ten thousand light years from the Sun, contains regions of star formation, and is illuminated by the light of one star cluster in particular, a cluster that formed within it some 3.5 million years ago. Relatively young in stellar terms, this cluster is designated Collinder 8 or IC 1590.

The cluster contains about three hundred stars in total, centred around the hot O-type star HD 5005 (designated 'B 1' or 'Burnham 1' by its discoverer, Sherburne Wesley Burnham). HD 5005 shines at eighth magnitude as seen from Earth, but at a distance of some ten thousand light years, this gives an absolute magnitude of approximately -4 (that is, at a standard distance of ten parsecs, it would rival the brightness of Venus in Earth's sky). This is a multiple star with at least four companions (and very possibly more) spread over a region of some twenty-six Astronomical Units.