Messier 102 — Galaxy in Draco

M102 is one of the most debated entries in the Messier catalog, with its identity uncertain for over two centuries. The object is most commonly identified as NGC 5866, the Spindle Galaxy, a lenticular (S0) galaxy in the constellation Draco located approximately 50 million light-years from Earth. Some historians believe M102 was simply a duplicate observation of M101. NGC 5866 is seen almost perfectly edge-on, displaying a razor-thin disk bisected by a prominent dark dust lane. The galaxy spans about 60,000 light-years in diameter and has a smooth, featureless envelope of older stars surrounding the disk. As a lenticular galaxy, it sits at the transition between elliptical and spiral types — it has a disk and dust lane like a spiral but lacks prominent spiral arms.

Located in Draco, NGC 5866 can be found about 2.5 degrees southwest of Iota Draconis. At magnitude 9.9, it appears as a small, elongated streak in a 4-inch telescope. An 8-inch telescope clearly shows the edge-on disk with a bright, concentrated nucleus. Under excellent conditions with 10 inches or more of aperture, the dark dust lane bisecting the galaxy becomes visible — a thin, dark line cutting across the bright disk. The galaxy's compact size (about 6 x 3 arcminutes) means it tolerates higher magnifications well. Best observed from April through September when Draco is high in the northern sky.

The confusion surrounding M102 dates to 1781, when Pierre Mechain reported it to Messier but later wrote a letter stating the observation was an error and M102 was actually a re-observation of M101. However, some researchers argue that Mechain's coordinates and description better match NGC 5866. Modern catalogs, including the Revised New General Catalogue, typically identify M102 as NGC 5866. The debate remains one of the most enduring mysteries in Messier catalog history.