The sky around Pinwheel Galaxy at true scale, north up and east left, with stars to magnitude 8. The circles show the field of a low-power eyepiece and of 10×50 binoculars.
Pinwheel Galaxy is a spiral galaxy in Ursa Major, 22 million light-years away
Pinwheel Galaxy (M101, NGC 5457, Arp 26, PGC 050063, UGC 08981) is a spiral galaxy in the constellation Ursa Major, 22 million light-years away. It shines at magnitude 7.9 and spans 29′ × 27′ of sky, about 186,800 light-years across. It is an easy target in binoculars, and it is highest in the evening sky in June.
Galaxy: a system of billions of stars, gas and dust held together by gravity, far outside the Milky Way. Spiral galaxies have a disk with arms; elliptical galaxies are smooth, round or oval swarms of older stars.
Pinwheel Galaxy is Arp 26, one of Arp's spiral galaxies with one heavy arm
Halton Arp photographed it for his Atlas of Peculiar Galaxies (1966) as field Arp 26. It is in his group of spiral galaxies, Arp 1 to 101, under the category Spiral galaxies with one heavy arm.
Pinwheel Galaxy lies 5.6° northeast of Alkaid, the magnitude 1.9 star. Three fingers held at arm's length cover about 5°.
Pinwheel Galaxy is highest in the evening in June
The chart gives its height above the horizon at 9 pm through the year, from 60°N to 40°S. It can be seen from the whole northern hemisphere and south to about 36°S, and never sets north of 36°N.
Pinwheel Galaxy is 22 million light-years away
The light seen from Pinwheel Galaxy tonight left it about 22 million years ago, long before modern humans existed. It ranks 79 of 109 by distance among the 110 Messier objects. Distance source: Cepheids, Riess 2022 (SH0ES).
