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)

Discovered before 964 AD by Al Sufi.

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.

This object is sometimes named Brocchi's Cluster after American amateur astronomer D.F. Brocchi, who created a map of it in the 1920s, for calibrating photometers. It was included in Per Collinder's 1931 catalog of open clusters.

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)

The image in this page was obtained by Till Credner and Sven Kohle of the University of Bonn, Germany when evaluating their Constellation Vulpecula photography. The photograph was obtained on August 8, 1999 at 23:57 UT from the Hoher List Observatory near Bonn, exposed 35 min on Kodak Royal 400 Select with a f=50mm 1/4.0 lens; original field of view is 39x27 degrees; ours is a magnification of a small part of this image. The (upside-down) coathanger is prominently visible in this image; it is equally obvious for visual observers with binoculars.

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 article and photometric data).

Observing Reports for Collinder 399 (IAAC Netastrocatalog)

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Hartmut Frommert
Christine Kronberg
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Last Modification: March 29, 1998