Click for larger image (50%)


Catalogue and alternative designations Westerlund 1, Ara cluster


Type Open cluster  (sometimes called a super star cluster)
Position 16 47 04, -45 51 05
Constellation Ara
Camera and Telescope STXL16200 and 36.8 cm RCOS Ritchey Chretien 
Focal Ratio F9
Exposure Details LRGB image using Astrodon filters.  Luminance = 150 minutes, Red = Green = Blue = 100 minutes. Luminance unbinned, colours binned 2x2.
Description Westerlund 1 is a very massive compact star cluster of great astrophysical interest.located about 15,000 light years away.  It is deeply reddened because of interstellar absorption and for this reason is best seen in the infrared. The cluster is very young, perhaps only 4-5 million years old  and contains one of the largest stars known,  the red hypergiant Westerlund 1-26 thought to have a diameter some 1500 times that of the sun. Westerlund 1 is sometimes termed a super star cluster. Clusters of this type are rare.