M-51 the Whirlpool Galaxy

M-51, the Whirlpool Galaxy

This is a CCD image taken with an STL-1301E CCD camera thru Kopernik's 20 inch F/8.1 telescope.

See info on Supernova 2011dh in M-51 on this page.

Charles Messier: (Jan. 11th, 1774) 'Very faint nebula without stars ... M. Messier discovered this nebula on the 13th of Oct. 1773, while observing the comet which appeared in that year. Seen only with difficulty in a 3,-foot telescope. Reported on the chart of the comet of 1773-74. It is double, each having a brilliant center, 4 min. 33 sec apart. The two atmospheres touching; one fainter than the other. Reviewed several times.'

Admiral W. Smyth: (1844) 'A pair of lucid white nebulae, each with an apparent nucleus with their nebulosity running into each other. The southern object is truly singular, having a bright center surrounded with luminosity, resembling the ghost of Saturn with his rings in a vertical position. A stellar universe, similar to that to which we belong, whose vast amplitudes are in no doubt peopled with countless numbers of percipient beings.'

W. Parsons, Earl of Rosse: (spring of 1845) 'Spiral convolutions; with successive increase of optical power, the structure has become more complicated . . .' 'The connection of the companion with the greater nebula is not to be doubted . . . the most conspicuous of the spiral class.' (and in 1861) 'The outer nucleus unquestionably spiral with a twist to the left.'

M-51(NGC 5194), the famous "Whirlpool Galaxy", is found South West from Eta Ursa Majoris, the end star of the Big Dipper's handle. The first galaxy found to show a spiral form, M-51 is about 35 million light years distant. It is 8th magnitude and about 10' in apparent diameter. M-51 is one of the nearest and brightest of the galaxies, and the one which shows the best-defined spiral structure. However, only fairly large telescopes show this spiral form.

Charles Messier discovered the brighter galaxy NGC 5194 in 1773 and his friend Pierre Mechain found the secondary nebula, NGC 5195, in 1781. In the early 20th century Nicholas Flammarion noted 'In the margin of Messier's manuscript of his catalogue, there is a note in his handwriting with a little sketch. "M. Mechain saw this nebula double - March 20th, 1781, saw this nebula; effectively it is double. The center of each is brilliant and clear; distinct and the light of each touches each other."'

The greatest telescopes resolve the spiral arms into a vast complex of star clouds, bright and dark nebulosity, individual stars, and nebulous knots which may be star clusters. The narrow dust lanes which define the spiral pattern extend deep into the nuclear region.

The two principal complexly structured dust lanes lie on the inner edges of the two major spiral arms. Their many branching filaments often cross the associated spiral arms at nearly right angles. The arms themselves can be traced for about one and a half turns and the spiral pattern is evident to within 15 arc seconds of the nucleus. The central mass has a mottled structure, and breaks up into a number of separate clouds, divided by thin dust lanes. The actual nucleus is about 2.7 seconds in diameter, and appears nearly stellar; the true diameter must be about 450 light years.

Satellite galaxy NGC 5195 may be attached to the north end of a M-51 spiral arm. Evidently it does not lie exactly in the plane of the big spiral, since dust lanes of the M-51 arm cross in front of it. There are also some dust patches on the opposite side, seemingly associated with the smaller galaxy itself. The classification of NGC 5195 is uncertain.

George Normandin, KAS

April 4th, 2008 - updated June 4, 2011