Brocchi's Cluster, Collinder 399

Right Ascension	19 : 25.4 (h:m)
Declination	+20 : 11 (deg:m)
Distance	0.42 (kly)
Visual Brightness	3.6 (mag)
Apparent Dimension	60 (arc min)

This cluster of about 40 stars was discovered by Al Sufi and described in 964 AD. It was independently rediscovered by Hodierna. Messier, the Herschels and the NGC did not assign it a number, probably because of the cluster's size: Even at moderate power, it doesn't match in one field of view, and is best seen in a good pair of binoculars. Also, its appearance suggests it might be an asterism only.

In 1970, investigations of Hall and Landingham revealed that perhaps only 6 of the brighter stars and none of the fainter ones appear to have a common proper motion, thus indicating that they may form a cluster. In the late 1980s, Pavlovskaya and Filipova were looking for common proper motion of open clusters, and found that the Coathanger was sharing spacial motion with about 10 other clusters, including the Plejades (M45), NGC 6633, 6709, 6882, 6885, and IC 4665. Collinder 399 was found to approach us at 18 km/sec. (info from Bernd Nies)

Brian Skiff of Lowell Observatory has investigated astrometrical data of the stars counted to Collinder 399 acquired by ESA's Hipparcos satellite, and found new evidence that this object may be an asterism instead of a cluster (Sky & Telescope).

Last Modification: 29 Mar 1998, 13:30 MET