- M 71
M 71 (NGC 6838) is a globular cluster in the constellation Sagitta. It was discovered by the Swiss astronomer Phillipe Loys de Cheseaux in 1745 or 1746. It was re-discovered by Johann Gottfried Kohler some time between 1772 and 1779. It was independently discovered in June of 1780 by Piere Mechain, Charles Messier's assistant. These various "discoveries" occurred because communications in Europe during these times did not facilitate wide distribution of information.
There was considerablr debate as to whether M 71 was a loose globular cluster or a rich open cluster (like M 11 in Scutum). Studies now suggest that it is a globular cluster. M 71 lies at a distance of 18,000 LY and has a relatively small size of only 40 LY across. It contains the equivalent of around 40,000 solar masses, which again is relatively low for a globular cluster. Comparing this image to my image of M 11, M 71 has a decidedly redder color, in part to its greater distance and also due to its older, redder population of stars.
The loose collection of stars about 2/3 of the way betwen M 71 and the right edge of my image is the open cluster Harvard 20. It contains around 28 stars and lies at a distance of approximately 8850 LY. The collection of relatively bright stars directly above M 71 in the image is not a cluster. The brightest star in that grouping is 9 Sagittae.
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