Pinwheel Galaxy (Messier 101)


The galaxy M 101 was discovered by Pierre Méchain on 27 March 1781. Charles Messier noted without having seen her: «Nebula without a star, very dark and very large, 6 to 7 minutes in diameter, between the left hand of the boat and the tail of the Great Bear. Hard to see if you illuminate the wires [of the micrometer].[281]

A number of star clouds and bright star formation areas in the spiral arms of M 101 were discovered on 14 April 1789 by Wilhelm Herschel and later on 1 March 1851 by Bindon Stoney, the engineer of Lord Rosse, and made it into NGC numbers in their own right Dreyer's «New General Catalogue of Nebulae and Clusters of Stars» published in 1888. In Halton Arp's 1966 Atlas of Peculiar Galaxies, M 101 is listed as Arp 26 for a galaxy with a thick arm. [199] The galaxy has received the nickname «Pinwheel Galaxy», a name that is sometimes also used for M 33, M 83 (Southern Pinwheel Galaxy) and M 99 (Coma Pinwheel Galaxy).

M 101
M 101: Galaxy M 101 in Ursa Major; TS Triplet APO 90, Reducer Photoline 0.79 (490mm / f5.44), SBIG ST-8300; 23L x 300sec 1×1, 12R, 15G, 15B 2×2 300sec, 14HA 2×2 600sec; Bernese Highlands; © 2018 Bernhard Blank, Dragan Vogel
M 101
M 101: Galaxy M 101 in Ursa Major; 500 mm Cassegrain 3625 mm f/7.2; SBIG STL11K; 90+30+30+30 min LRGB; Bernese Highlands; © 2011 Radek Chromik
M 101
M 101: Approximate visually visible detail in a larger amateur telescope; 5" Refractor; © 2004 Eduard von Bergen, Hansjörg Wälchli

Physical Properties

The galaxy M 101 is of the morphological type SAB(rs)cd, has a heliocentric speed of about 237 km/s to 241 km/s. Distances range from about 5 Mpc to 7 Mpc. M 101 measures around 170,000 light years in diameter, almost twice the size of our Milky Way. It is believed that the galaxy contains at least a trillion stars. The spiral arms are peppered with large nebulae in which stars are born and clusters of hot, blue, young stars. [145, 194, 215]

Revised+Historic NGC/IC, Version 22/9, © Dr. Wolfgang Steinicke [277]
NameRADecTypebMagvMagDimDreyer DescriptionIdentification, Remarks
NGC 544714 02 29.0+54 16 21GxyP13.51pB, S, R, gmbM, conn with M 101NGC 5450, part of M 101
NGC 544914 02 28.2+54 19 53GxyP14.01vF, pL, gvlbM, all conn with M 101part of M 101
NGC 545014 02 29.0+54 16 21dup13.01F, pS, iR, glbM, all conn with M 101NGC 5447, part of M 101
NGC 545114 02 36.5+54 21 49GxyP14.00.3vF, pL, iR, vlbM, all conn with M 101part of M 101
NGC 545314 02 56.7+54 18 31GxyP13.80.5F, pL, lE, vlbM, conn w M 101part of M 101
NGC 545514 03 01.0+54 14 27GxyP13.00.4pB, pS, R, psbM, conn w M 101part of M 101 (or C gxy?)
NGC 545714 03 12.4+54 20 58Gx (Sc)8.37.928.8 × 26.9pB, vL, iR, g, vsmbMBSNM 101, UGC 8981, MCG 9-23-28, IRAS 14013+5435, CGCG 272-21, KARA 610, Arp 26, VV 344, VV 456, Pinwheel galaxy
NGC 545814 03 12.4+54 17 56GxyP14.00.6vF, pL, R, vlbM, conn w M 101HII in M 101
NGC 546114 03 41.5+54 19 05GxyP14.00.6B, pS, R, psbM, conn with M 101part of M 101
NGC 546214 03 53.0+54 22 02GxyP13.51pB, pL, iR, gbM, conn with M 101part of M 101
NGC 547114 04 28.9+54 23 51GxyP15.514.70.6 × 0.5F, S, R, * 12·13 pMCG 9-23-30, VV 394, part of M 101

Finder Chart

Above the two stars on the tip of the Big Dipper, one reaches the sprial galaxy M101 by forming an equilateral triangle with the stars Alkaid (η Ursae Majoris) and Mizar (ζ Ursae Majoris).

Chart Pinwheel Galaxy (Messier 101)
Pinwheel Galaxy (Messier 101) in constellation Ursa Maior. Chart created using SkySafari 6 Pro and STScI Digitized Sky Survey. [149, 160]

Visual Observation

350 mm aperture: The brighter core can already be observed with small instruments. The fine spiral arms can only be seen under extremely good observation conditions and with the help of medium-sized amateur instruments. The weak spiral arms with their knots are clearly visible in a 12.5 or 14 inch telescope. [192]

14" PWO-Dobson, F:4.6 / TV-Nagler 13mm, 123x, 0.67° und TV-Panoptic 19mm, 84x, 0.81°
Eduard von Bergen

More Objects Nearby (±15°)


145SIMBAD astronomical database;
149SkySafari 6 Pro, Simulation Curriculum;
160The STScI Digitized Sky Survey;
192Deep-Sky Guide; (2020-12-25)
194NASA/IPAC Extragalactic Database (NED); (2020-12-27)
199«Atlas Of Peculiar Galaxies», Halton Arp, 1966; Astrophysical Journal Supplement, vol. 14, p.1 (1966); DOI:10.1086/190147; Bibcode:1966ApJS...14....1A
215Explore - The Night Sky | Hubble’s Messier Catalog; (2020-12-31)
277«Historische Deep-Sky Kataloge» von Dr. Wolfgang Steinicke; (2021-02-17)
281«Catalogue Nébuleuses et des Amas D'Étoiles» Observées à Paris, par M. Messier, à l'Observatoire de la Marine, hôtel de Clugni, rue des Mathurins. «Connoissance des temps ou connoissance des mouvements célestes, pour l'année bissextile 1784 » Page 227; (2021-02-21)