2012 08 23 – NGC6475 /M7
2012 08 23, 0409 UT – NGC6475 /M7
Erika Rix – Liberty Hill, Texas
AT6RC f/9 1370mm, LXD75, 38mm Titan (70 degree FOV), 36x
78.8F, 54% H, calm/clear, Pickering 6, T 2/6
Open cluster in the constellation Scorpius containing 80 stars, Tr Type I 3 r, 017h 53.9m, -34deg49´, 80´, m3.3v, distance 820 ly, diameter ~20 ly.
In the 2nd century A.D., Ptolemy noted M7 and M6 as little clouds (unaided eye). Charles Messier cataloged it in June 1764. It’s located as a brightened haze between the “sting of Scorpius” and the handle of the teapot asterism in Sagittarius, just SE of M6.
M7 was fairly low on the horizon just above the sky glow from Austin to the south. Altitude was 28 degrees at the beginning of the sketch then lowered to 19 degrees by the end of the observation. The wide FOV of the 38mm Titan gave wonderful views nonetheless. The faintest stars were difficult to see and I detected them with averted vision. Once they were located, I could see them straight on. The center of the open cluster was “cross-shaped” at first site. Once the fainter stars were plotted in the sketch, the cross turned into two arcs touching in the middle (one facing north, the other south) with opened ends pointed away from each other. I wish I could say that star color was noted, but other than a couple that perhaps had slight orange tinges, they were all fairly similar color-wise to me. There were several pairs and triplets of star in the cluster.