M 108

Spiral Galaxy M108 (NGC 3556), type Sc,

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.

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 8×1′.

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.