Pinwheel Galaxy
spiral galaxy in the constellation Ursa Major
The Pinwheel Galaxy (also known as Messier 101, M101 or NGC 5457) is a face-on, counterclockwise intermediate spiral galaxy located 21 million light-years (6.4 megaparsecs) from Earth in the constellation Ursa 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.
On February 28, 2006, NASA and the European Space Agency released a very detailed image of the Pinwheel Galaxy, which was the largest and most detailed image of a galaxy by Hubble Space Telescope at the time. The image was composed of 51 individual exposures, plus some extra ground-based photos.
Discovery
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 illuminates 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 with 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.
Though the galaxy can be detected with binoculars or a small telescope, to observe the spiral structure in a telescope without a camera requires a fairly large instrument, very dark skies, and a low-power eyepiece.
Structure and composition
M101 is a large galaxy, with a diameter of 252,000 light-years. By comparison, the Milky Way has a diameter of 87,400 light-years.
The public source identifies “Pinwheel Galaxy” as spiral galaxy in the constellation Ursa Major. This brief keeps that definition visible, then builds a research path around Pinwheel, Galaxy and spiral.
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Vocabulary and entity names are the principal evidence signals here, because they determine the precision of every later search. The source revision retrieved here is dated Sep 4, 2026. The linked authority identifier is Q14371. None of the 0 selected statements returned an explicit reference. The first chronological checks are 1781, 2006 and 1784.
The absence of detail may reflect summary conventions rather than a lack of surviving documentation. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
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This entry incorporates text from “Pinwheel Galaxy” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.