NGC 188 is an open cluster located in the far northern constellation of Cepheus. It was discovered by John Herschel - the son of William Hershel - on November 3, 1831. He originally recorded it as h 34 in his 1833 catalogue and then included it as GC 92 in his subsequent General Catalogue of 1864. The cluster finally became NGC 188 in John L.E. Dreyer's New General Catalogue of 1888.

NGC 188 is the northernmost open cluster in the sky, it's positioned only 4.75 degrees from the North Celestial Pole. Located at such a northerly declination means the cluster is circumpolar from almost the entire northern hemisphere. It can be seen from the Southern Hemisphere but only from latitudes north of 5 degrees south. Even then it never climbs more than a few degrees above the northern horizon.

NGC 188 - Open Cluster (Roberto Mura)

Finder Chart for NGC 188

Finder Chart for NGC 188 - pdf format

With an apparent magnitude of +8.1, NGC 188 is visible through binoculars but not easily. On dark nights of excellent seeing it can be spotted with 7x50 or 10x50 binoculars, appearing as a faint dim patch of light. The cluster has a low surface brightness and is better seen using at least a medium size telescope. A 150mm (6-inch) instrument reveals a soft glow that initially appears unresolved but on further inspection a sprinkling of faint stars can be seen. The brightest cluster members shine at 12th magnitude and there are at least 130 stars brighter than 17th magnitude. Through a 250mm (10-inch) scope, NGC 188 is a wonderful sight with dozens of stars scattered like stardust across the entire cluster face, which spans 15 arc minutes in diameter.

Studies indicate that NGC 188 is the most ancient of all known open clusters. It's estimated to be at least five billion years old. For comparison, M45 The Pleiades cluster in Taurus is a youthful 115 million years ago. Once factor that certainly contributed to the longevity of NGC 188 is that it lies well away from the plane of the galaxy and therefore rarely passes through high-density galactic regions.

Since most open star clusters are young they typically contain many luminous hot blue giant stars. These type of stars are short lived and as a result old clusters like NGC 188 tend to contain more yellow and red stars and are almost devoid of blue stars.

NGC 188 has an actual diameter of 33 light-years and is estimated to be about 5,000 light-years distant. It's also the first object in the Caldwell catalogue.

NGC 188 Data Table

NGC188
Caldwell1
Object TypeOpen Cluster
ConstellationCepheus
Distance (ly)5,000
Apparent Mag.+8.1
RA (J2000)00h 47m 30s
DEC (J2000)85h 14m 29s
Apparent Size (arc mins)15 x 15
Radius (light-years)11
Age (years)5 Billion
Number of Stars>130
Other Name (s)Collinder 6
Notable FeatureMost northerly open cluster in the sky

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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