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What is χ and h

double star cluster chi and h Persei
The Perseus Double Cluster. χ Per is left and h Per is right. They are just under 1° apart.

χ Persei and h Persei look like the names of stars, but they are in fact two open star clusters. It was Bayer in 1603 who introduced the naming of stars with a greek letter and the name of the constellation they belong to (here Perseus, Persei being the genitive). Usually the order of the letters in the greek alphabet is the same as the magnitude order of the stars within the constellation, so that e.g. α Per is the brightest star in Perseus. All 88 constellations have a three letter abbreviation of their genitive, hence "Per" stands for "Persei" or "of Perseus".

In dark skies the double cluster is visible as a hazy patch of light about midway between the constellations of Perseus and Cassiopeia (the W-shaped constellation north of Perseus). Hipparchus and Ptolemy already mention these objects as a nebular or cloudy spot, at least as far back as 150 BCE. In contrast, Charles Messier never included these objects in his catalogue. The modern-day professional names are from Herschel's New General Catalogue - NGC869 (h Per) and NGC884 (χ Per). Each cluster appears about 30 arcmin in diameter and contains 300 or 400 stars. The brightest stars are about 7th magnitude and would on their own not be visible to the naked eye. The clusters are about 7000 or 8000 light years away. They are probably not a true pair. Rather, χ Per is thought to be almost 1000 light years further away than h Per. (Robert Burnham, Jr., (1978). Burnham's celestial handbook, An observer's guide to the universe beyond the solar system, Dover Publications, New York, p.1438ff.)