Finder Chart for Jim’s Pick of the Month May 2021 Messier 101: Pinwheel Galaxy

FACTS Object: Galaxy Type: Spiral Class: SAB(rs)cd Designations: Messier 101, M101, NGC 5457 Constellation: Ursa Major Right ascension: 14h 03m 12.6s Declination: +54°20’57” Distance: 20.9 million light years (6.4 megaparsecs) Number of stars: 1 trillion Apparent magnitude: +7.86 Absolute magnitude: -21.6 Apparent dimensions: 28′.8 x 26′.9

Radius: 85,000 light years Messier 101. Image: European Space Agency & NASA

Messier 101 (M101), also known as the Pinwheel Galaxy, is a spiral galaxy located in the constellation Ursa Major, the Great Bear. The Pinwheel Galaxy has an apparent magnitude of 7.86 and lies at a distance of 20.9 million light years from Earth. It has the designation NGC 5457 in the New General Catalogue.

The galaxy is quite large, but has a low surface brightness and requires exceptionally clear, moonless skies to be seen, even in medium-sized telescopes. The Pinwheel Galaxy can be spotted in 10×50 binoculars under exceptionally good conditions, but only appears as a large, faint patch of light. Small telescopes only reveal the galaxy’s brighter central region, while the spiral structure appears as patchy nebulosity in 4-inch instruments. 8-inch telescopes show the galaxy’s dense core surrounded by a fainter halo dotted with patches of nebulosity and hinting at the spiral structure.

Messier 101 is easy to find because it is located just above the handle of the Big Dipper. It forms a triangle with Alkaid and the double star Mizar/Alcor. It can be found 5.5 degrees northeast of Alkaid and at the same angular separation from Mizar. The best time of year to observe the Pinwheel Galaxy is during the spring.