Messier 102

Right Ascension	15 : 06.5 (h:m)
Declination	+55 : 46 (deg:m)
Distance	45000 (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.

The object Messier 102 (M102) was recorded by Pierre Méchain in late March or early April, 1781, and included by Charles Messier in his catalog without verifying before publication, and without giving a position. Lateron, Méchain did disclaim the discovery, stating that this was an accidental duplication of his discovery, M101, but Messier added a handwritten position for M102. This situation has given rise to a long-standing controversy, where two opinions on the identity of this object are common:

1. M102 might be a duplication of the Spiral Galaxy M101 (NGC 5457) in Ursa Major, due to a possible error of either the catalog author Messier, or its `discoverer' Méchain, a view brought up by Méchain in a letter of May 1783.
2. Perhaps more probably (due to historical evidence), M102 may be the Lenticular Galaxy NGC 5866 in Draco, also sometimes called the Spindle Galaxy, as Messier's catalog description indicates, together with the position he added later by hand in his personal copy.

The authors of this page think that there is sufficient evidence that both Méchain and Messier have probably observed NGC 5866 in context of this catalog entry. Therefore, it should be considered to take this last missing object back into the catalog, and we will take this object for M102 in the following.

Please note our discussion of more details on this topic.

M102 is a beautiful lenticular galaxy in Northern constellation Draco, which is seen almost exactly edge-on, showing a prominent dust lane along its equatorial plane.

M102 (NGC 5866) was probably first seen by Pierre Méchain in March 1781, or by Charles Messier shortly after that time. 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 this 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 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.

M102 is a beautiful lenticular galaxy of visual magnitude 9.9, according to newer references; the older Sky Catalogue 2000.0 gives mag 10.0, while Don Machholz has estimated it at 9.6. It is seen almost exactly edge-on. The fine dark dust lane shows up nicely in our 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.

The distance of M102 (NGC 5866) is estimated 45 million light-years distant (an earlier estimate by Burbidge and Burbidge (1960) was 40 million light-years, while R. Brent Tully's Nearby Galaxies Catalog has the slightly larger value of about 50 million light-years). At this distance, its diameter of 5.3' corresponds to a linear extension of about 69,000 light-years.

This galaxy is the brightest member of a remarkable group of galaxies, the M102 group or NGC 5866 group of galaxies. This group also contains the big and 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 including NGC 5870, NGC 5866A (=Turn 121A), NGCs 5866B (= UGC 9769), UGC 9776 and M+10-22-10 (PGC 54577). NGCs 5862, 5867, 5874 and 5876 as well as IC 1099 are faint background galaxies within the field of this group, similar to the nearby background galaxy pair NGC 5905 and NGC 5908. From the dynamics of that group, E.M. and G.R. Burbidge (1960) have estimated M102's mass to be about 1 trillion solar masses, so it is a considerably massive galaxy. No supernovae have been discovered in this galaxy yet.

Our image of M102 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.

M102 (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 M102 or NGC 5866 group, mentioned above, can also be spotted with amateur instruments (in particular NGC 5907). 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 102.7 ly distance from us; recently, it was claimed that a planet had been discovered orbiting this star (some info on Iota Draconis and its planet).

Potentially interesting trivia about M102 (NGC 5866): With its ecliptical latitude of about 67 degrees North, the Earth's North Celestial Pole passes within less than a degree of it, at periods of the precession of Earth's axis (about 25,800 years). So this galaxy was "Polarissima Borealis" about 6900 years ago (4900 BC) and will become again in 18900 years (20900 AD).

NGC Online data for M102 (NGC 5866)

References:

• E.Margaret Burbidge and G.R. Burbidge (1960), Distortion of the Plane of the Occulting Matter in NGC 5866. Astrophysical Journal, Vol. 131, pp. 224-226 [ADS: 1960ApJ...131..224B]

Further reading:

• S. Pellegrini, 1994. ROSAT PSPC observation of the X-ray faint early-type galaxy NGC 5866. Astronomy and Astrophysics, Vol. 292, No. 2, p. 395-403 [ADS: 1994A&A...292..395P]
• M. Hamabe, K. Kodaira, S. Okamura, and B. Takase, 1979. Surface Photometry of Edge-on Galaxies. I. NGC 5866. Publications of the Astronomical Society of Japan, Vol. 31, pp. 431-450 (1979) [ADS: 1979PASJ...31..431H]
• Zhong Wang and Xiaohui Hui, 1994. Rotation Curve of Molecular Gas in the Center of Early Type Galaxy M102. American Astronomical Society Meeting, 184, #49.02, May 1994. [ADS: 1994AAS...184.4902W]

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Hartmut Frommert
Christine Kronberg
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Last Modification: May 7, 2013