M71, an open cluster

There was much discussion as to whether M71 was a globular cluster or an open cluster.  It is a bit too open to be a globular but a bit too compact to be an open, so it is now referred to as a loose, globular cluster.  It was first observed by Loys de Cheseaux in 1745-6 and catalogued by Messier as M71 in 1780.  It is 13,000 light-years away within the Milky Way galaxy and so there are many stars in the foreground and background that are unrelated to the cluster, making it difficult to tell where the cluster starts and finishes.  The main part appears to subtend an angle of 5-6 arc-minutes which corresponds to about 27 light years.

	My first attempt at this cluster. Date and Time: 8th July 2007 00:35 UT Camera: Atik ATK1 HS Telescope: LX200 with 0.33 focal reducer (focal length 800 mm) Capture: K3CCDTools. High gamma, exposure 5 sec, 91% gain, 72 frames Processing: K3CCDTools. 44 frames stacked, histogram 0-180, unsharp mask 3,0,400
	My equipmment and my technique have improved over the years since 2007 and here is a much sharper picture of M71.  The main reason is the use of the MX716 camera, active guiding, and the non-linear enhancement from the star_mx7 software.  This latter increases the contrast in the dark areas of the picture and reduces it in the bright areas (very like a positive gamma correction) so that many more faint stars become visible. Date and Time: 16th August 2016 22:32 to 22.47 UT Camera: Starlight Xpress MX716 Telescope: LX200 with 0.33 focal reducer (focal length 800 mm) Capture: Star_mx7. 30 sec exposure, 34 frames collected of which many were marred by passing cloud. Processing:           Star_mx7. Dark subtraction, non-linear stretch factor 25           Irfanview. Conversion from FIT to PNG format           RegiStax 5. Align and stack 13 frames, wavelets 1-2=5, step=0           PhotoImpact. Small drift compensation in Focus Magic, and reduction in size.

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