NGC 2506 is a magnitude +7.6 rich open cluster located in the constellation of Monoceros. Although its member stars are faint the cluster itself appears quite bright and can be seen with a pair of binoculars. Through telescopes it's an impressive object and of all the Monoceros open clusters it's probably the finest. With an age of 1.1 billion years old this is an old cluster. For comparison, M45 (The Pleiades) in Taurus is a youthful 115 million years old with the Hyades cluster 625 million years old. However, NGC 2506 is not nearly as old as the 4 billion years of M67 in Cancer.

William Herschel discovered NGC 2506 on February 23, 1791. Locating the cluster can sometimes be a bit tricky as it's positioned in an area of sky devoid of bright stars. It can be found 5 degrees east-southeast of alpha Mon (α Mon - mag. +3.94) the brightest star in Monoceros. Located 19 degrees southwest of NGC 2506 is the brightest star in the sky, Sirius (α CMa - mag. -1.46). Although α Mon and Sirius are the brightest stars in their respective constellations the difference in apparent brightness between them is enormous, more than 100x.

Large open cluster M48 lies 6 degrees northeast of NGC 2506 with open cluster pair M46 and M47 positioned 6 degrees southwest of NGC 2506. They are best seen during the months of December, January and February.

NGC 2506 - Open Cluster (Jim Thommes -

Finder Chart for NGC2506

Finder Chart for NGC2506 - pdf format

NGC 2506 appears as a faint small misty unresolvable patch of light in 7x50 or 10x50 binoculars. A 100mm (4-inch) telescope under dark skies reveals about a dozen stars embedded in hazy, misty patch of light. Through 200mm (8-inch) scopes, NGC 2506 is a wonderful sight. At high magnifications more stars are visible, arranged in chains streaming across the face of the cluster. The brightest member stars are of magnitude +10.8 and the cluster contains at least 150 stars packed in an apparent diameter of 7 arc minutes. A 300mm (12-inch) scope resolves many more stars with NGC 2506 appearing more compact at the edges than in the centre. This is a wonderful object and a superb cluster for amateur astronomers, especially those with medium or larger sized scopes. In the Caldwell catalogue, NGC 2506 is listed as number 54.

NGC 2506 Data Table

Object TypeOpen Cluster
Distance (ly)11,300
Apparent Mag.+7.6
RA (J2000)08h 00m 02s
DEC (J2000)-10h 46m 11s
Apparent Size (arc mins)7.0 x 7.0
Radius (light-years)12
Age (years)1.1 Billion
Number of Stars150
Other Name (s)Collinder 170, Melotte 80

Sky Highlights - March 2017

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

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
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)
Southeast:- Jupiter (mag. -2.3 to -2.5)
Southwest:- Jupiter
Southeast:- Saturn (mag. +0.5)

Southern Hemisphere
West:- Venus (first half of month), Mars, Uranus
North:- Jupiter
East:- Saturn
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)

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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