NGC 869 and NGC 884, also known as h and Chi Persei, are two of the finest star clusters in the sky. This splendid group contains some of the most brilliant stars known and is visible with the naked eye as a hazy patch between Cassiopeia’s W and the pointed top of Perseus.
It is believed that this Double Cluster in Perseus has been known since pre-historical times, but was first catalogued only about 150 BC by the Greek astronomer Hipparcos. He referred to it as a “nebula” or “cloudy spot”, one of the half dozen then recognized. The true nature of such objects remained a mystery until the invention of the telescope in the early 1600’s. This beautiful object was never included by Charles Messier in his famous catalogue, although he included other bright clusters such as the Beehive and the Pleiades.
Binoculars show each of the clusters to have over a hundred stars, with the westernmost, NGC 869, appearing more compact. The two clusters cover an area two times the size of a Full Moon, with NGC 869 being the brighter and richer of the pair.
If you observe with a telescope, a low power wide-angle eyepiece with a field of about one degree is required in order to get both clusters in the field. Short focus telescopes of the RTF (rich-field) design are excellent for objects of this type. A few M-type red supergiant stars can be seen in NGC 884 with small telescopes, but none in NGC 869. Both clusters lie in a nearby spiral arm of the galaxy just over 7000 light-years away and are about 70 light-years across.
Finder map – field width 30 degrees, stars to magnitude 7.