NGC 5866 / M102 ?

Lenticular (S0) Galaxy NGC 5866 (M102 ?), type S0_3, in Draco

Spindle Galaxy

Right Ascension 15 : 06.5 (h:m)

Declination +55 : 46 (deg:m)

Distance 40000 (kly)

Visual Brightness 9.9 (mag)

Apparent Dimension 5.2x2.3 (arc min)

Right Ascension	15 : 06.5 (h:m)
Declination	+55 : 46 (deg:m)
Distance	40000 (kly)
Visual Brightness	9.9 (mag)
Apparent Dimension	5.2x2.3 (arc min)

Discovered probably either by Pierre Méchain or by Charles Messier in 1781.
Independently discovered by William Herschel in 1788.

NGC 5866 is a beautiful lenticular galaxy of visual magnitude 10.0 or 9.6 (the first value from Sky Catalogue 2000.0, the latter is an estimate by Don Machholz). It is seen almost exactly edge-on. The fine dark dust lane shows up nice in this image; it is tilted by about 2 degrees against the galaxy's symmetry plane, for which John Herschel and the NGC give the position angle 146 deg, and the Deep Sky Field Guide to Uranometria 2000.0 gives 128 deg. Longer exposures overexpose the dust lane so that this galaxy was often misclassified as elliptical of type E6 instead of the correct type S0_3 (some sources have even classified it as Sa), see e.g. the comparison of 2 images in Sandage's Hubble Atlas of Galaxies, plate 6. They show however an extended system of globular clusters. See also the Digital Sky Survey image.

This galaxy is situated in the northern constellation Draco at RA 15h 06.5, Dec +55d 46' (2000.0). It is the brightest of a remarkable group of galaxies (the NGC 5866 group), lying roughly 40 million light-years distant (R. Brent Tully's Nearby Galaxies Catalog has the slightly larger value of about 50 million light-years), which also contains the big bright edge-on spiral NGC 5907 (type Sb+, 10.4 mag vis), the fainter galaxy NGC 5879 (Sb, 11.5), and more very faint galaxies (NGCs 5866B (= UGC 9769), 5862 5905, 5908 and IC 1099; NGC 5866A (Turn 121A) is a faint background galaxy within the field of this group, similar to the nearby background galaxy pair NGC 5905 and NGC 5908. Faint UGC 9776 is another probable member listed occasionally. From the dynamics of that group, E.M. and G.R. Burbidge (1960) have estimated NGC 5866's mass to be about 1 trillion solar masses, so it is a considerably massive galaxy. The 5.2' diameter of NGC 5866 correspondes to about 60,000 light-years, its globular cluster halo extends more far outward. No supernovae have been discovered in this galaxy yet.

NGC 5866 was probably first seen by Pierre Méchain in March 1781, or by Charles Messier shortly after that time. Therefore, NGC 5866 is possibly M102, although Pierre Méchain disclaimed the discovery two years later. Pierre Méchain's first observing report caused Messier to include it as entry No. 102 in his catalog, without giving a position or further verification. Soon after, Messier added a position measurement for this object (or entry) to his personal copy of the catalog, probably shortly after publication and still in 1781. There is evidence that Charles Messier has probably observed NGC 5866 when measuring this position, as it is almost exactly 5 degrees preceding (west) of the actual position of the object, very probably a data reduction error of some kind. Nevertheless, this subject is still somewhat dubious and therefore controversial. If, despite this evidence, it should be true that neither Méchain nor Messier have observed NGC 5866, it was probably first seen by William Herschel (or perhaps by Caroline Herschel) when independently discovering it in 1788; William Herschel determined its position on May 5, 1788. As the possible earlier sightings by Méchain and Messier did not result in a published position for this object, this galaxy bears Herschel's number H I.215.

Admiral Smyth, probably following an error by John Herschel in his 1833 catalog, confuses its number with H I.219 (which is NGC 3665, a galaxy in Ursa Major), and thus erroneously gives that object's discovery date, March 1789.

Our image of NGC 5866 was provided by Stephan Korth. It was taken by Bernd Koch and Stefan Korth, on 12 March 1995 at 1:09 UT with a Celestron 14 at f=4.060mm, located at the Sternwarte Aufderhöhe near Solingen, Germany. The camera was a Starlight XPress, exposure time 5m 28s. Image processing was done with PIXWIN and Corel PhotoPaint by the authors.

NGC 5866 can be found rather easily, and along the description given by Méchain despite his disclaimer, from Iota Draconis (Edasich, mag 3.29, spectral type K2 III), about 3 deg SW in the direction of Eta Ursae Majoris (Alkaid, mag 1.9, sp B3 III) or Theta Bootis (mag 4.06, sp F7 V); a star of mag 5.21 (GC 20332 = HD 134190 = SAO 29407) is nearby and to the south.

This galaxy is well visible in a 4-inch telescope as a considerably bright elliptical or spindle-shaped nebulous object with a brighter core, notable even in smaller instruments; several faint stars are visible around it. Larger telescopes show more details, in particular the dust lane and the brighter ends, and a mottled or grainy texture of the outer parts of the galaxy.

Some of the neighboring member galaxies of the NGC 5866 group, mentioned above, can also be spotted with amateur instruments. Very close to the galaxy is the difficult and almost stellar NGC 5867, listed as nonexistent in the RNGC, but it is actually a galaxy and not a star. The star used to locate NGC 5866, Iota Draconis (also 12 Dra, Edasich) is a red giant at about 150 ly distance from us; recently, it was claimed that a planet had been discovered orbiting this star.