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, which at a distance of 24,500 light-years corresponds to a spatial diameter of 160 light-years, making it one of the largest globulars in both apparent and actual size.

M5 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, recording 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 in the night sky. M5 is positioned 4 degrees east of 110 Her (mag. +4.4) and next to a small triangle of 6th magnitude stars. At 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 (credit:- NASA, The Hubble Heritage Team (AURA/STScI))

Finder Chart for M5 (credit:- freestarcharts)

Finder Chart for M5 - pdf format (credit:- freestarcharts)

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

Sky Highlights - January 2017

Conjunction
Mars passes just 1 arc minute south of Neptune on January 1, 2017

Comet
Comet 45P/Honda-Mrkos-Pajdusakova now visible with small telescopes

Meteor Shower
Quadrantids meteor shower peaks on January 3, 2017

Minor Planet
Vesta now visible with binoculars and small telescopes. Reaches opposition on January 17, 2017

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for January 2017

Northern Hemisphere
Evening
Southwest:- Venus (mag. -4.4 to -4.7), Mars (mag. +0.9 to +1.1), Neptune (mag. +8.0)
South:- Uranus (mag. +5.8)
Midnight
West:- Uranus
East:- Jupiter (mag. -1.9 to -2.1)
Morning
South:- Jupiter (mag. -1.8)
Southeast:- Saturn (mag. +0.6), Mercury (mag. -0.2 second half of month)

Southern Hemisphere
Evening
West:- Venus, Mars, Neptune
Northwest:- Uranus
Midnight
East:- Jupiter
Morning
Northeast:- Jupiter
East:- Saturn, Mercury (second half of month)

Deep Sky
Naked eye / binoculars:-
Messier 45 - M45 - The Pleiades (Open Cluster)
The Hyades - Open Cluster
NGC 869 and NGC 884 - The Double Cluster - Open Clusters
Messier 31 - M31 - Andromeda Galaxy (Spiral Galaxy)
Messier 42 - M42 - The Great Orion Nebula (Emission/Reflection)

Small telescopes:-
NGC 457 - Owl Cluster - Open Cluster
Messier 103 - M103 - Open Cluster
Messier 36 - M36 - Open Cluster
Messier 37 - M37 - Open Cluster
Messier 38 – M38 - Open Cluster

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