A star catalogue having its origins in the Harvard Photometry Survey of 1884, which was initially restricted to the northern hemisphere, and the Harvard Revised Photometry Survey of 1908, which incorporated both hemispheres of the sky. The BrightStar Catalogue lists starsbrighter than magnitude +6.50 (that is, the nearly ten thousand stars that would be visible to the naked eye under absolutely ideal conditions).
A comprehensive catalogue of brightstars originating at Harvard College Observatory, and later expanded by astronomers at Yale University, and a system of stellar designation based on this catalogue. Stars, especially those lacking Bayer letters or Flamsteed numbers, are often identified by their BSC catalogue number, usually prefixed by 'HR', but with numbers sometimes listed with the prefixes 'BSC' or 'BS'.
The catalogue is designed to list all the stars in the sky brighter than magnitude +6.50. This is the effective limit for naked-eye visibility under ideal conditions, so the catalogue lists every star that can be seen with the naked eye. In common with other similar catalogues, stars are numbered from west to east, starting at the celestial meridian. HR 1 is a faint star in Andromeda at right ascension 00h07, and the numbering continues around the sky following increasing right ascension until it reaches HR 9110 (or V567 Cassiopeiae) a variablestar in Cassiopeia.
Catalogue numbers in the BrightStar Catalogue are assigned in ascending order of right ascension, counting eastward from the Celestial Meridian. The highlighted star in this image is HR 1 in Andromeda, the first star in the catalogue, which lies just six and a half arcminutes eastward of the meridian. Imagery provided by Aladin sky atlas
The BrightStar Catalogue had its origins in the index Harvard Photometry published in 1884, which collated data for brightstars in the skies of the northern hemisphere. A revised edition, published in 1908, included stars from the southern sky to create a comprehensive catalogue. This Revised Harvard Photometry is the source of the 'HR' ('Harvard Revised') prefix that is usually applied to star numbers from the BrightStar Catalogue. The data for its standard list of stars has been extensively reviewed, extended and annotated since the original catalogue's publication, with the first Yale BrightStar Catalogue appearing in 1930, and being periodically updated since that time.
While the focus of the BrightStar Catalogue is, naturally, brightstars, the catalogue does in fact list a few objects that are not bright, or are not stars. In the former category are a number of novae, stars that once shone brightly enough to be included but, after a brief flare in magnitude, have now faded far beyond naked-eye visibility. Also included are a small number of objects that are not single stars, but clusters. Two of these are prominent globular clusters (47 Tucanae and NGC 2808, or HR 95 and HR 3671), and two are open clusters (M67 and NGC 2281, or HR 3515 and HR 2496).
