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| M73, A Open Cluster, - Click on photo above for a full frame full rez image. |
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M73 is a little conspicuous assortment of four stars
of 10th to 12th magnitude, situated in the very western part of
constellation Aquarius only about 1.5 deg east of globular cluster M72. It
is classified as an open cluster but its nature as a physical group of
gravitationally linked stars is in some doubt. There has always been a
significant fraction of astronomers who believed that M73 is an asterism, a
chance alignment of 4 stars at different distances.
Although M73 consists of only 4 stars, Charles Messier found, logged (October 4, 1780), and described it as follows:
Apparently, this group found its way into Messier's catalog because he had determined its position at the same time when measuring M72, which is 1.5 degrees to the west. It may have been included because of its "first-glance nebulous" appearance in Messier's instruments. Although it is clear from his description that this group was what Messier had observed and measured, some versions of Messier's catalog omit it as an "obscure" object, possibly because they couldn't see any "commentary" nebulosity as they presumed Messier had. This "Y"-shaped group of stars is well visible in 4-inch telescopes; the fourth star is notably fainter and difficult in these instruments. It is best found from M72 which is almost at the same declination (very slightly North) and 1.5 deg West. The 4.5-mag star Nu Aquarii, mentioned by Messier, is about 2deg North and 1.5 deg to the West. |
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10"
F6.3 Schmidt Cassegrain Telescope, (1600mm F.L.) Modified Canon
300D camera with IR-UV filter, placed at the scopes prime focus |