Degree of difficulty 2 (of 5)

Minimum aperture 30mm

Designation NGC 7654

Type Open cluster

Class I2r

Distance 4630 ly (K2005) 4470 ly (2001)

Size 22 ly

Constellation Cassiopeia

R.A. 23h 24.8min

Decl. +61° 36′

Magnitude 6.9

Surface brightness –

Apparent diameter 16′

Discoverer Messier, 1774

History M 52 is another chance discovery by Charles Messier, made while he was following a comet. The French observer noted, on the 7 th of September 1774: “Cluster of very small stars, which cannot be seen except in an achromatic refractor, mingled with nebulosity.”

50 years later, John Herschel described this cluster and saw “a ruddy star of 9 th magnitude in the preceding [western] part of a pretty rich irregular cluster of stars of 13th magnitude, all separate, 6' diameter; a very little more compressed in the south following [southeastern] part.”

His countryman Admiral Smyth commented on M 52: “This object assumes somewhat of a triangular form, with an orange-tinted 8th magnitude star at its vertex, giving it the resemblance of a bird with outspread wings. It is preceded by [east of] two stars of 7th and 8th magnitudes, and followed by [west of] another of similar brightness; and the field is one of singular beauty under a moderate magnifying power.” With his large telescope, Lord Rosse estimated that there were 200 cluster stars.

Curtis referred to the photographic appearance of the cluster when he wrote: “A very sparse, open cluster 16' in diameter, of stars 12th –16 th magnitude.”

Astrophysics After M 11, M 52 is one of the richest open clusters in the Messier list. In 1959, Wallenquist counted 193 cluster members within a radius of 9'. More recent sources state 130 cluster stars and 30 field stars down to 14 th magnitude, plus more than 6000 cluster stars and about as many field stars down to magnitude 19.5.