M102 is a galaxy catalogued by Charles Messier that hasn't been explicitly identified. It was Pierre Mechain who made the original observation in March 1781 before passing the information onto Messier, who catalogued it without verification. However, Mechain himself believed M102 was an error and wrote a letter on the May 6, 1783 expressing his view that the object was in fact a duplicate entry of M101. The story does not end there, historical evidence based on Messier description of the galaxy combined with its co-ordinates suggest that M102 could well be lenticular galaxy NGC 5866, also known as the Spindle galaxy. A number of other possible candidates have been suggested but it seems both Messier and Mechain have observed NGC 5866 in the past and therefore we list it as the missing item.

The Spindle galaxy (mag. +9.9) is located at the southern edge of the far northern constellation of Draco. It's positioned four degrees southwest of star Iota Draconis (ι Dra - mag. +3.3). Directly west of NGC 5866 are the seven stars that form the famous "Plough" or "Big Dipper" asterism of Ursa Major.

NGC 5866 is a challenging binocular object but easier to spot with small scopes. It's best seen from the Northern Hemisphere during the months of April, May and June. From latitudes of 35N or greater, the galaxy is circumpolar and therefore never sets.

M102 the Spindle Galaxy by the Hubble Space Telescope (NASA, The Hubble Heritage Team (AURA/STScI))

Finder Chart for M102 (also shown M51 and M101)

Finder Chart for M102 (also shown M51 and M101) - pdf format

A small 80mm (3.1-inch) telescope under dark skies shows NGC 5866 as a thin saucer shape smudge of nebulosity that spans 4.7 x 1.9 arc minutes. Through a 150mm (6-inch) or 200mm (8-inch) scope the galaxy appears as a halo of greenish tinged light that hints at the dark dust lane. It has a well-defined bright central core with larger scopes revealing more intriguing details. Photographically NGC 5866 is a beautiful sight with the almost edge on dusk disk spectacular.

The Spindle galaxy is located 50 million light-years distant and has a radius of 70,000 light-years. It's estimated to contain about 100 billion stars.

M102 Data Table

Object TypeLenticular Galaxy
Distance (kly)50000
Apparent Mag.9.9
RA (J2000)15h 06m 29s
DEC (J2000)55d 45m 47s
Apparent Size (arc mins)4.7 x 1.9
Radius (light-years)35,000
Number of Stars100 Billion
Notable FeatureDisputed Messier object

Sky Highlights - April 2017

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