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)[5] away from Earth in the constellation Ursa Major. It was discovered by Pierre Méchain in 1781[a] and was communicated that year to Charles Messier, who verified its position for inclusion in the Messier Catalogue as one of its final entries. [1]
M101 is a large galaxy, with a diameter of 170,000 light-years. By comparison, the Milky Way has a diameter of between 100,000 and 120,000[13] light-years. It has around a trillion stars.[14] It has a disk mass on the order of 100 billion solar masses, along with a small central bulge of about 3 billion solar masses.[15] Its characteristics can be compared to those of Andromeda Galaxy. [1]
The giant spiral disk of stars, dust and gas is 170,000 light-years across — nearly twice the diameter of our galaxy, the Milky Way. M101 is estimated to contain at least one trillion stars. The galaxy’s spiral arms are sprinkled with large regions of star-forming nebulas. These nebulas are areas of intense star formation within giant molecular hydrogen clouds. Brilliant, young clusters of hot, blue, newborn stars trace out the spiral arms. [2]
[1]
https://en.wikipedia.org/wiki/Pinwheel_Galaxy[2]
https://www.nasa.gov/feature/goddard/2017/messier-101-the-pinwheel-galaxy
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