M102 is a galaxy catalogued by Charles Messier that hasn't yet been explicitly identified. It was Pierre Méchain who made the original observation in March 1781, before passing the information onto Messier who catalogued it without verification. However, Méchain believed M102 was an error and even wrote a letter on May 6, 1783 expressing his view that the object was in fact a duplicate of M101. Historical, evidence based on Messier's 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 emerged, but it seems likely that Messier and Méchain both at some time observed NGC 5866, and therefore we include 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 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 much easier to spot with small scopes. It's best seen from Northern Hemisphere locations during the months of April, May and June. From latitudes of 35N or greater, this galaxy is circumpolar and therefore never sets.
Under dark skies, small 80mm (3.1-inch) refractors show NGC 5866 as a thin saucer shape smudge of nebulosity spanning 4.7 x 1.9 arc minutes. Through 150mm (6-inch) or 200mm (8-inch) reflectors, it appears as a halo of greenish tinged light with a well-defined bright central core. The view also hints at the dark dust lane that spans the length of the galaxy. Photographically, NGC 5866 is a beautiful sight with the dusk disk spectacular.
The Spindle galaxy is located 50 million light-years away and has a radius of 70,000 light-years. It's estimated to contain about 100 billion stars.
M102 Data Table
|Object Type||Lenticular Galaxy|
|Distance (light-years)||50 Million|
|RA (J2000)||15h 06m 29s|
|DEC (J2000)||+55d 45m 47s|
|Apparent Size (arc mins)||4.7 x 1.9|
|Number of Stars||100 Billion|
|Notable Feature||Disputed Messier object|