Spindle Galaxy

Messier 102 is the only genuinely controversial entry in Messier's catalog — its true identity has been debated for over two centuries. Pierre Méchain, who originally reported it in 1781, later wrote that it was probably an erroneous duplication of his earlier observation of M101, an explanation many astronomers accept. However, a number of careful investigators — comparing Méchain's original positional description with the actual sky — argue persuasively that both Méchain and Messier had actually observed NGC 5866, a lenticular galaxy in the constellation Draco also known as the Spindle Galaxy, and it is NGC 5866 that is shown here.

NGC 5866 is a lenticular galaxy of type S0 — structurally intermediate between ellipticals and spirals. Like an elliptical, it has a smooth, relatively featureless body dominated by an old stellar population with little ongoing star formation; like a spiral, it possesses a disk component, visible here as a dramatically thin, dark dust lane cutting directly across the galaxy's equatorial plane. This edge-on orientation makes NGC 5866 one of the most striking lenticular galaxies in the sky, its perfectly bisecting dust lane creating a sharp two-toned disk that no edge-on spiral could replicate. The galaxy lies approximately 50 million light-years from Earth and spans about 60,000 light-years.

In a small telescope NGC 5866 / M102 appears as a spindle-shaped oval with a slightly brighter nucleus; the dark equatorial dust lane becomes visible in apertures of 150 mm or more under good conditions. This image was made with the T2KA CCD camera at the Kitt Peak National Observatory 0.9-meter telescope in March 1995.