Messier 36, NGC 1960 and permanent object 173 identify the same open cluster in Auriga. An open cluster is a population born together from one molecular cloud, held only loosely enough that Galactic tides and encounters can eventually disperse it. Gaia astrometry lets researchers distinguish members from unrelated foreground and background stars by their common parallax and motion rather than by position alone.
A comprehensive Gaia DR2 study found most M36 member candidates between 0.7 and 0.9 milliarcsecond in parallax, with a median of 0.82 ± 0.07 milliarcsecond, corresponding to about 1.20 ± 0.13 kiloparsecs or 3,900 light-years. Its radial density profile gave a diameter of 27.0 ± 0.4 arcminutes, about 9.4 parsecs at that distance. The authors estimated an age near 15 million years and emphasized that M36 is free of nebulosity. Source: [Panja et al., *The Astrophysical Journal* 910, 80, data and abstract](https://cdsarc.cds.unistra.fr/viz-bin/cat/J/ApJ/910/80).
The word “free” describes the present optical cluster, not proof that star formation began without gas. Massive young stars heat and ionize their surroundings; winds, radiation and supernovae can clear the remaining material. Meanwhile the lower-mass population is harder to inventory against the Milky Way field. Membership counts therefore depend on probability thresholds and survey sensitivity, while the distance and age come from fitting a population, not measuring every member independently.
Giovanni Battista Hodierna recorded the cluster before 1654, although that work was only recovered by modern historians. Guillaume Le Gentil independently found M36 in 1749. Charles Messier observed it on September 2, 1764 and described a cluster of stars with no nebulosity. Source: [SEDS biography and account of Le Gentil's Auriga discoveries](https://messier.lamost.org/seds/seds.org/messier/en/xtra/Bios/legentil.html). That early description and the modern infrared and astrometric result agree on what is absent, even though only modern data explain the stars as a shared young population.
The stored position is approximately right ascension 5h 36m and declination +34° 08′. M36 culminates about 79° high from latitude 45° N but only 21° from 35° S. These are geometric altitudes; extinction near a low horizon and weekly timing belong to the observing calendar.
Use the pentagon of Auriga as the large-scale frame. Capella is too far away for a tight eyepiece hop: M36 is about 12.4° from it. A more useful deep-sky comparison is M38, about 2.28° northwest of M36 from the stored catalogue positions; M37 is about 3.75° to the east-southeast. Sweep at low power through the rich winter Milky Way, confirm the compact cross-like knot of brighter members, and only then increase magnification. The calculated relationships are guides, not a substitute for checking the rendered accepted finder and reader link, which remain unverified.
Common catalogues give M36 an integrated magnitude around 6.3, but its light is divided among stars over a broad field. Source: [AstroPixels M36 data](https://www.astropixels.com/openclusters/M36-01.html). Binoculars show a small granular patch; a small telescope resolves the brighter blue-white members, and moderate power separates the central pattern from the Milky Way background. The 27-arcminute research diameter exceeds the tighter bright core often quoted by observing guides, so “size” depends on membership depth. Record the unresolved patch and resolved member pattern separately, and do not claim nebulosity simply because unresolved stars make a haze.
