This 30-minute exposure at F/5.5 shows only the inner portion of M-33. It resolves many of this relatively close galaxy's brightest stars.
M-33, known as "the Pinwheel Galaxy", is one of the bright members of the Local Group of Galaxies, and probably the nearest spiral galaxy after the Andromeda system, M-31. It is one of the notable discoveries of Charles Messier. Messier thought the apparent size to be about 15'. J.E.Bode, in 1775, saw it as "a faintly illuminated nebulous patch of disorderly shape".
CHARLES MESSIER: (Aug. 25th, 1764) 'The nebula is a whitish light of almost even brightness. However, along two-thirds of its diameter it is a little brighter. Contains no star......'.
Quote from The Publications of Lick Observatory, Volume XIII:
'A close rival to M-31 as the most beautiful spiral known. With its faintest extensions it covers an area of at least 55'X40'. it is uncertain whether there is an actual stellar nucleus. A multitude of stellar condensations in the whorls. Best example of resolution into stars.'
M-33 is a challenging object for the small telescope because of its great size and rather low surface brightness. While some find it easily visible in binoculars, or even with the naked eye, others report complete inability to see the galaxy at all. Many observers look for a much smaller and brighter object, rather than a dim glow comparable in apparent size to the Moon. Sky conditions are critical, and inexperienced observers often use too high a power on small instruments. Faint and extended luminous objects are visible only because of contrast against the sky background; dark skies and wide-angle eyepieces are essential. M-33 is easily visible in large binoculars.
With modern telescopes, M-33 is the easiest of all galaxies to resolve; masses of star clouds and even bright individual stars show clearly in our CCD images. M-33 is revealed as a huge double-armed spiral of star clouds curving about the bright nuclear mass. The arms are thick and clumpy, dotted with nebulous regions, and the spiral structure is loose and irregular when compared with such symmetrical galaxies as M-81. NGC 604, which is one of the most conspicuous of the separate 'knots' in M-33, has been found to have a spectrum similar to the Orion Nebula, M-42. The outermost diameter of 90 arc minutes corresponds to 60,000 light years at the accepted distance of 2.5 million light years. The rotational period in the region of the rim has been measured at about 200 million years.
George Normandin, KAS
January 25th, 2009