M36 is the first of three bright Messier open clusters located in the southern part of the constellation of Auriga (the other two are M37 and M38). It was discovered by Italian astronomer Giovanni Batista Hodierna sometime before 1654 and catalogued by Charles Messier on September 2, 1764. At mag. +6.2, the cluster is at the limit of naked eye visibility and therefore easily visible in binoculars, appearing as a small fuzzy patch of light. M36 is concentrated, containing at least 60 known members and covers 12 arc minutes of apparent sky. This makes it a particularly nice object for owners of small / medium sized telescopes. The cluster is best seen from the Northern Hemisphere during the months of December, January and February.
Finding M36 is not difficult once one is familiar with the northern constellation of Auriga, the Charioteer. Locating Auriga is easy. It's a bright grouping of stars with a prominent large polygon at its core. Neighbouring constellations include Taurus and Gemini. The northern star of the polygon is brilliant, Capella (mag. +0.08). Located 7.5 degrees east of Capella is Menkalinan (β Aur - mag. +1.9) and 8 degrees due south of Menkalinan is θ Aur (mag. +2.65). From θ Aur, draw an imaginary line in a southwesterly direction for 11 degrees until you reach another bright star. This star is El Nath (β Tau - mag. +1.65), which straddles the border between Auriga and Taurus. Located just west of the mid-point of the line connecting θ Aur and El Nath is M36.
M36 along with neighbour M37 can be spotted with the naked eye from exceptionally dark sites, both appearing as faint patches of light. M38 shines at mag. +7.0 and is therefore beyond naked eye visibility, even from the dark locations. All three are easily within the range of good binoculars, with M36 looking like a compact fuzzy patch of light, that hints at resolution. Binoculars with a sufficiently wide field of view (at least 6 degrees), allow the observer to view M36, M37 and M38 all at the same time. When viewed through larger binoculars or small telescopes, the fuzziness of M36 is transformed into a sprinkling of stars. An 80mm (3.1-inch) telescope at low / medium powers reveals about 15 or so bright members scattered throughout the cluster. Most stars appear white or bluish white and are arranged in an "X" type shape or a pointed starfish. The brightest stars are of 8th and 9th magnitude and are very luminous B type blue stars of the order of 350 times more luminous than our Sun. Prominent near the center of the cluster is a double star with 10th magnitude components, separated by 10 arc seconds.
A large 150mm (6-inch) telescope reveals approximately 25 stars. Switch to averted vision and the view is practically unchanged with hardly any extra stars visible. Progressively larger telescopes will show more and more stars with a 300mm (12-inch) telescope resolving most of them.
M36 is superb open cluster that's about 4,100 light-years distant. It has an apparent diameter of 12 arc minutes, which corresponds to a spatial diameter of 14 light-years. It's the smallest of the three Auriga Messier open clusters and the least populated. However, M36 does contain a number of individually bright stars compared to the other clusters. In total, M36 has 60 known members and is easily visible in binoculars. Any telescope will at least partly resolve this fine cluster with larger telescopes completely resolving it. Spatially, M36 is a similar size cluster to that of the famous Pleiades (M45) and would appear at least as bright and spectacular as M45, if it were located as close. Since it's a young cluster of only about 25 million years age, M36 contains mainly hot white / blue-white stars and no red giants, unlike its neighbours M37 and M38.
M36 Data Table
|Object Type||Open Cluster|
|RA (J2000)||05h 36m 18s|
|DEC (J2000)||+34d 08m 27s|
|Apparent Size (arc mins)||12 x 12|
|Age (years)||25 Million|
|Number of Stars||60|
|Other Name||Collinder 71|