The
Pinwheel Galaxy (also known as
Messier 101,
M101 or
NGC 5457) is a face-on
spiral galaxy 21 million
light-years (6.4
megaparsecs) away from Earth in the
constellationUrsa Major. It was discovered by
Pierre Méchain in 1781 and was communicated that year to
Charles Messier, who verified its position for inclusion in the
Messier Catalogue as one of its final entries.Pierre Méchain, the discoverer of the galaxy, described it as a "nebula without star, very obscure and pretty large, 6' to 7' in diameter, between the left hand of Bootes and the tail of the great Bear. It is difficult to distinguish when one lits the [grating] wires."
William Herschel wrote in 1784 that the galaxy was one of several which "...in my 7-, 10-, and 20-feet [focal length] reflectors shewed a mottled kind of nebulosity, which I shall call resolvable; so that I expect my present telescope will, perhaps, render the stars visible of which I suppose them to be composed."
Lord Rosse observed the galaxy in his 72-inch-diameter
Newtonian reflector during the second half of the 19th century. He was the first to make extensive note of the spiral structure and made several sketches.To observe the spiral structure in modern instruments requires a fairly large instrument, very dark skies, and a low-power eyepiece.
Source: Wikipedia
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