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M 108

Spiralna galaksija - Spiral Galaxy M108 (NGC 3556), type Sc, in ursa Major

Rektascenzija 11 : 11.5 (u:m)
Deklinacija +55 : 40 (sto:m)
Razdalja 45000 (*1000 sv.l.)
Vizual. magnituda 10.0 (mag)
Zorni kot 8x1 (loc min)

M108, together with M109 was probably discovered by Pierre Mechain in the same night when he found M97 (February 16, 1781), and observed by Charles Messier when he measured the position of M97 (March 24, 1781). Messier measured an acurate position at a later time which he added by hand in his personal copy of the catalog. The object M108 was finally added to Messier's catalog by Owen Gingerich in 1953. William Herschel has cataloged it as H V.46.

The nearly edge-on galaxy M108 appears to have no bulge and no pronounced core at all, it is just a detail-rich mottled disk with heavy obscuration along the major axis, with few H II regions and young star clusters exposed against the chaotic background -- in a word: "Very Dusty". There's little evidence for a well-defined spiral pattern in this Sc galaxy, which is receding at 772 km/sec. According to Brent Tully, it is about 45 million light years distant, and a member of the Ursa Major cloud, a loose agglomeration of galaxies. Tully classifies this galaxy as SBcd, i.e. very late Sc, and with a bar; the present author can find no evidence for such a notion in the images he knows.

The type II supernova 1969B occurred in M108 and reached mag 13.9 on Jan 23, 1969.

M108 is quite easy for the amateur, easier than the published values of its brightness (exception: Don Machholz' estimate of mag 9.4) imply. Well matching in the opinion of the present author is John Mallas' description as a "silver-white beauty, saucer-shaped and very well defined" with a quite bright and irregular central region, surrounded by "light and dark nodules." It is a very elongated object with angular dimensions 8x1'. It is actually surprising how much detail can be seen in this galaxy with small instruments ! Color photos show an even more conspicuous appearance of this should-be showpiece, which often appears in wide field and "deep spatial depth" photos together with the Owl nebula M97, which is only about 48' to the SE.

Vec posnetkov M108

Povzeto po:
Hartmut Frommert (spider@seds.org)
Christine Kronberg (smil@lrz.uni-muenchen.de)

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