Sky Object of the Month – October 2014
Messier 30 – Globular Cluster in Capricornus
by Glenn Chaple
During October, Ophiuchus, Scorpius, and Sagittarius depart the evening sky, taking with them their ample cargo of globular star clusters. A few stragglers remain accessible to backyard telescopes – among them, Messier 30 in Capricorn.
M30 was discovered by Messier in 1764. He described it as a round nebula, containing no stars. Its stellar nature fell to the watchful eye of William Herschel, who resolved M30 twenty years later.
Recently, I observed M30 from a suburban location on an evening when the naked eye limit was about 5th magnitude. It was readily visible through 10 X 50 binoculars, appearing as an out-of-focus 7th magnitude star just a half degree west of the 5.5 magnitude star 41 Capricorni. A 4-inch f/10 reflector at 120X didn’t resolve any stars, but it did reveal M30’s highly concentrated nucleus. In my 10-inch f/5 reflector at 208X, the outer parts of M30 were resolved. The cluster spanned some 5-6 arc-minutes and seemed elongated in an east-west direction. Two stellar streams radiated outward towards the north.
M30 lies about 27.000 light-years from earth. It harbors several hundred thousand stars and has an estimated diameter of 90 light-years.
photo by Mario Motta, MD freestarcharts.com