M75, magnitude +8.7, is a very distant and compact globular cluster located in eastern Sagittarius. At 67,500 light-years, it's one of the remotest Messier globulars and from our perspective appears faint and small. This cluster lies far beyond the galactic centre (46,700 light-years) and almost on the opposite side of the galaxy to the Solar System. Despite this, it's intrinsically bright and on nights of good seeing and transparency can be glimpsed with a pair of 7x50 or 10x50 binoculars.

M75 was discovered by Pierre M├ęchain on the night of August 27, 1780. Charles Messier observed it soon afterwards and added it to his catalogue a few weeks later. It was William Herschel who first resolved M75 into stars, describing it as a "miniature version of M3." He also gave the same description to M62 and M70.

M75 is located at the Sagittarius-Capricornus border. It's positioned about 23 degrees northeast of the centre of the Sagittarius teapot asterism and 5.5 degrees north and a little east of a small group of four faint naked-eye stars (59 Sagittarii - mag. +4.5, 60 Sagittarii - mag. +4.8, 62 Sagittarii - mag. +4.4 and ω Sgr - mag. +4.7).

The cluster is best seen during the months of June, July and August from southern and tropical locations.

M75 globular cluster (credit:- NOAO/AURA/NSF)

Finder Chart for M75 (credit:- freestarcharts)

Finder Chart for M75 - pdf format (credit:- freestarcharts)

Finder Chart for M72 (also shown M30, M73 and M75) (credit:- freestarcharts)

Finder Chart for M72 (also shown M30, M73 and M75) - pdf format (credit:- freestarcharts)

For binocular observers, M75 appears stellar in nature. A 100mm (4-inch) telescope at high magnifications will reveal a certain degree of fuzziness. However, the cluster is small and spans visually only 3 arc minutes in diameter. It's roughly comparable in size and brightness to the other Messier globulars located within the teapot, M54, M69 and M70. To begin resolution, large reflectors of at least 250mm (10-inch) aperture are required.

In total M75, covers 6.8 arc minutes of apparent sky, which corresponds to a spatial diameter of 134 light-years. It's very old at 13 billion years and is estimated to contain 400,000 stars. Classified as class I, M75 is one of the most densely concentrated globulars known. However despite been faint and small, it's a remarkable object to observe given its incredible distance.

M75 Data Table

Messier75
NGC6864
Object TypeGlobular cluster
ConstellationSagittarius
Distance (light-years)67,500
Apparent Mag.+8.7
RA (J2000)20h 06m 05s
DEC (J2000)-21d 55m 17s
Apparent Size (arc mins)6.8 x 6.8
Radius (light-years)67
Age (years)>13 Billion
Number of Stars400,000
Notable FeatureDistant globular and one of the most densely concentrated clusters known

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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