Messier 13, M13, NGC6205 Hercules, Great Globular Cluster
M13 is a large and bright globular cluster in Hercules, discovered by Halley in 1714, and documented by Messier in 1764. The cluster is composed of about 300,000 members with a total mass of 500,000 solar masses. The brightest star in the cluster is a Cepheid variable V11 with apparent magnitude of 11.9. The cluster is 22,200 LY distant, 145 LY in diameter, and subtends an angle of 20 arcmin. It is 11.65 billion years old, and contains ancient stars of low metallicity, created long before succeeding generations of supernovas enriched the galaxy with heavy elements. With apparent magnitude of 5.8, it is visible to the naked eye under good conditions, and easily identified in binoculars. A 4 inch telescope is needed to begin to resolve stars.
In the left lower corner is NGC 6207, an 11.65 mag galaxy, 2' 31'' in angular size, and lying at the distance of 64 million LY.
The attached, reprocessed image was taken with a TSAPO100Q astrograph, Sigma APO 1.4x tele-extender, unmodified Canon 600D camera, Astronomik CLS-CCD filter, Celestron AVX mount, and Orion 60mm F4 SSAGpro autoguider.
The image is a stack of 7 x 240 sec exposures at iso1600, 25% crop, 2x drizzle, processed with 30 dark and 30 bias frames. Actual FL is 812mm, apparent FL about 1600mm, and limiting magnitude 17. Note the small 11.7 magnitude, 3 arcmin galaxy NGC6207 in the left lower corner.
Software used was PHD2, DSS, XnView, StarTools, and Neat Image.
Thank you for looking. C&C welcome.