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Messier 5 - M5 - Globular Cluster

M5 is a superb globular cluster that's located close to the celestial equator in the constellation of Serpens (Caput). Shining at magnitude +5.7, it's visible to the naked eye under dark skies, appearing as a faint "star". The cluster is large, covering 23 arc-minutes of apparent sky. At a distance of 24,500 light-years from Earth this corresponds to a spatial diameter of 160 light-years, making M5 one of the largest globulars in terms of both apparent and actual size.

It was discovered by Gottfried Kirch and his wife Maria Margarethe on the May 5, 1702. At the time, the couple were observing a comet when they stumbled across the cluster and noted it as a star with nebulosity. Charles Messier found it independently 62 years later on the May 23, 1764, describing it as a round nebula which "doesn't contain any stars". The first person to resolve the cluster into stars was William Herschel, who counted 200 of them using his 40-foot (12.2 meter) focal length reflector in 1791.

M5 is located 23 degrees southeast of orange giant star Arcturus (α Boo), which at mag. –0.04 is the fourth brightest star. It's positioned 4 degrees east of 110 Her (mag. +4.4) and next to a small triangle of 6th magnitude stars. The northern tip of the triangle is double star 5 Ser (mag. +5.0) with M5 located just northwest of this star.

Messier 5 globular cluster by the Hubble Space Telescope (NASA, The Hubble Heritage Team (AURA/STScI))

Finder Chart for M5

Finder Chart for M5 - pdf format

Under very good viewing conditions, M5 can be just about glimpsed with the naked eye as a faint point of light. With binoculars, it's easily visible as small fuzzy patch. A small 80mm (3.1-inch) telescope reveals a bright glowing core wrapped inside a much fainter halo of nebulosity. A 100mm (4-inch) telescope under excellent skies will start to resolve individual stars, the brightest of which are 11th magnitude. A 150mm (6-inch) scope at high power resolves more of the outer edges of M5. Through larger scopes it's a spectacular sight with thousands of stars coming into view, radiating like chains or legs outwards from the bright centre. The cluster appears noticeably elongated with a compact and somewhat clumpy core. Overall, M5 is a beautiful globular cluster that's best seen during the months of March, April and May.

With an estimated age of 13 billion years, M5 is one of the oldest Milky Way globular clusters. It's estimated to contain at least 500,000 stars. A total of 105 variable stars have been observed of which 97 belong to the RR Lyrae type. Also a dwarf nova has been observed in M5.

M5 Data Table

Messier5
NGC5904
Object TypeGlobular cluster
ConstellationSerpens
Distance (kly)24.5
Apparent Mag.5.7
RA (J2000)15h 18m 34s
DEC (J2000)02d 04m 58s
Apparent Size (arcmins)23 x 23
Radius (light years)80
Age (years)13,000M
Number of Stars>500,000
Notable FeatureA dwarf nova has been observed in this globular

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Current Bright Comets

Comet Lovejoy (C/2014 Q2)
Puppis, mag +6.7 (Dec 11).
NH - Not visible.
SH - Visible high in the sky.

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