M15 star cluster

M15 Globular Star Cluster

M15 is a magnitude 6.3 globular star cluster in the constellation Pegasus. It can be detected with binoculars under dark skies. M15 is a rich compact globular star cluster, and displays a relatively bright central core when viewed through a telescope. This star cluster ranks as the 12th brightest globular cluster visible in the sky. The cluster is 10 arc-minutes in diameter.

M15 was discovered by Maraldi while he was searching for the de Cheseaux comet in September 1746. A globular star cluster looked like a comet in the crude telescopes in use back in those days, and Maraldi would have had to observe it for several hours to determine whether it moved. Messier found it in 1764 and added it to his catalog, so that if he came across it again he would not waste time watching it to see whether it displayed the motion of a comet.

This is an RGB color CCD image taken with an ST-8E CCD on a Takahashi FS-128 refractor with a reducer operating at f5.9. A nearby magnitude 7.6 star known as SAO 107179 is bright enough to bloom a digital camera even using short exposures, and thus makes it a challenge to get a good image of M15. I stacked a number of short exposures, but still got some blooming from that star that had to be removed from the final image. The image was taken from my backyard.

M15 (NGC 7078)
Constellation: Pegasus
RA: 21h 30m 09s Dec: +12d 10' 59"
August 10, 2003
Image by Sid Leach
Scottsdale, Arizona

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