Messier 101

Big, beautiful spiral galaxy M101 is one of the last entries in Charles Messier's
famous catalog, but definitely not one of the least. About 170,000 light-years,
this galaxy is enormous, almost twice the size of our own Milky Way galaxy.
M101 was also one of the original spiral nebulae observed by Lord Rosse's large
19th century telescope, the Leviathan of Parsontown. Assembled from 51 exposures
recorded by the Hubble Space Telescope in the 20th and 21st centuries, with
additional data from ground based telescopes, this mosaic of M101 is touted as
the largest, most detailed spiral galaxy view ever released from Hubble. The
sharp image shows stunning features along the galaxy's face-on disk of stars and
dust along with background galaxies, some visible right through M101 itself.
Also known as the Pinwheel Galaxy, M101 lies within the boundaries of the
northern constellation Ursa Major, about 25 million light-years away.