M12 is a magnitude +7.2 globular cluster in Ophiuchus that was discovered by Charles Messier on May 30, 1764. He was unable to resolve the cluster, describing it as "nebula without stars". It was William Herschel who first managed this in 1783. Through good binoculars, M12 appears as a faint hazy patch of light that's not well defined. Positioned nearby is the slightly brighter but similar looking globular M10. The two clusters are among the brightest of the seven Messier globulars located in Ophiuchus.

M12 is located in a barren area of sky that's devoid of bright stars and therefore finding it can require some patience. Start by locating Rasalhague (α Oph - mag +2.1) the brightest star in Ophiuchus. Join the stars of Ophiuchus in a curve heading westwards and southwards until arriving at two close together 3rd magnitude stars, Yed Prior (δ Oph - mag. +2.7) and Yed Posterior (ε Oph - mag. +3.2). M12 is located about 8 degrees northeast of the stars. Positioned 3.25 degrees southeast of M12 is M10, with the star 30 Oph (mag. +4.8) located one degree east of M10.

The best time of the year to observe M12 is during the months of May, June and July.

M12 globular cluster by the Hubble Space Telescope (credit:- NASA, The Hubble Heritage Team (AURA/STScI))

Finder Chart for M12 (credit:- freestarcharts)

Finder Chart for M12 - pdf format (credit:- freestarcharts)

M12 is not a particularly concentrated globular cluster and was once believed to be an intermediate type object, something between a globular and a dense open cluster, such as M11. A small 80mm (3.1-inch) telescope reveals a fuzzy mottled ball that's obviously non-stellar. At medium to high powers, a 200mm (8-inch) scope resolves the clusters brightest stars with at least twenty pinpoints of light scattered throughout. Also visible are lines and branches of stars extending outwards from the diffuse center core. The core itself is not particularly bright or well defined. In total, the globular covers 16 arc minutes of apparent sky and on good nights, large amateur telescopes will show stars across the entire face of the cluster.

M12 is located at a distance of 18,000 light-years and is estimated to be 12.6 billion years old. It has a spatial diameter of 80 light-years and contains 70,000 stars. The brightest member star is of mag. +12.0.

M12 Data Table

Messier12
NGC6218
Object TypeGlobular cluster
ConstellationOphiuchus
Distance (light-years)18,000
Apparent Mag.+7.2
RA (J2000)16h 47m 14s
DEC (J2000)-01d 56m 52s
Apparent Size (arc mins)16 x 16
Radius (light-years)40
Age (years)12.6 Billion
Number of Stars70,000

Sky Highlights - March 2017

Comet
Comet 41P/Tuttle-Giacobini-Kresak now visible with binoculars as it heads towards perihelion

Mercury
Mercury heading towards greatest elongation east

Minor Planet
Vesta now visible with binoculars and small telescopes.

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for March 2017

Northern Hemisphere
Evening
West:- Venus (mag. -4.8 to -4.1 - first half of month), Mars (mag. +1.3 to +1.5), Uranus (mag. +5.9), Mercury (mag. -1.5 to -0.4 - second half of month)
Midnight
Southeast:- Jupiter (mag. -2.3 to -2.5)
Morning
Southwest:- Jupiter
Southeast:- Saturn (mag. +0.5)

Southern Hemisphere
Evening
West:- Venus (first half of month), Mars, Uranus
Midnight
North:- Jupiter
East:- Saturn
Morning
West:- Jupiter
Northeast:- Saturn
East:- Neptune (mag. +8.0 - second half of month)

Deep Sky
Naked eye / binoculars:-
Melotte 111 - Mel 111 - The Coma Star Cluster (Open Cluster)
Messier 44 - M44 - The Praesepe (Open Cluster)

Telescopes:-
Messier 67 - M67 - Open Cluster
Messier 51 - M51 - The Whirlpool Galaxy (Spiral Galaxy)
Messier 97 - M97 - The Owl Nebula (Planetary Nebula)
Messier 101 - M101 - The Pinwheel Galaxy (Spiral Galaxy)
Messier 65 – M65 – Spiral Galaxy
Messier 66 - M66 - Intermediate Spiral Galaxy
Messier 95 - M95 - Barred Spiral Galaxy
Messier 96 - M96 - Intermediate Spiral Galaxy
NGC 4244 - Spiral Galaxy
NGC 4565 - Needle Galaxy - Spiral Galaxy

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