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 - July 2017

The Planets
This Month's Guide

Algol Minima
Algol eclipse dates and times for July

Meteor Shower
Southern Delta Aquariids (Aquarids) meteor shower peaks on July 29

Northern Hemisphere
Evening
West:- Mercury (mag. -0.5 to +0.3) (second half of month)
Southwest:- Jupiter (mag. -2.0)
South:- Saturn (mag. +0.2)
Midnight
West:- Jupiter
South:- Saturn
East:- Neptune (mag. +7.8)
Morning
Southwest:- Saturn
South:- Neptune
Southeast:- Uranus (mag. +5.8)
East:- Venus (mag. -4.1)

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

Deep Sky

Small telescopes:-
Messier 13 - M13 - Great Hercules Globular Cluster
Messier 92 - M92 - Globular Cluster
Messier 11 - M11 - The Wild Duck Cluster (Open Cluster)
Messier 7 - M7 - The Ptolemy Cluster (Open Cluster)
Messier 6 - M6 - The Butterfly Cluster (Open Cluster)
Messier 4 - M4 - Globular Cluster
Messier 8 - M8 - Lagoon Nebula (Emission Nebula)
Messier 16 - M16 - Eagle Nebula (Emission Nebula with Open Cluster)
Messier 20 - M20 - Trifid Nebula (Emission and Reflection Nebula)

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