Messier 3

Coordinates: Sky map 13h 42m 11.23s, 28° 22′ 31.6″
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Messier 3
Messier 3 - Adam Block - Mount Lemmon SkyCenter - University of Arizona.jpg
Globular cluster Messier 3 in Canes Venatici
Observation data (J2000 epoch)
ConstellationCanes Venatici
Right ascension13h 42m 11.62s[2]
Declination+28° 22′ 38.2″[2]
Distance33.9 kly (10.4 kpc)[3]
Apparent magnitude (V)6.39[4]
Apparent dimensions (V)18′.0
Physical characteristics
Absolute magnitude-8.93
Mass4.5×105[5] M
Radius90 ly
Tidal radius113 ly (30 pc)[mean][6]
Metallicity = –1.34[7] dex
Estimated age11.39 Gyr[7]
Other designationsNGC 5272[8]
See also: Globular cluster, List of globular clusters

Messier 3 (M3; also NGC 5272) is a globular cluster of stars in the northern constellation of Canes Venatici.


It was discovered on May 3, 1764,[9] and was the first Messier object to be discovered by Charles Messier himself. Messier originally mistook the object for a nebula without stars. This mistake was corrected after the stars were resolved by William Herschel around 1784.[10] Since then, it has become one of the best-studied globular clusters. Identification of the cluster's unusually large variable star population was begun in 1913 by American astronomer Solon Irving Bailey and new variable members continue to be identified up through 2004.[11]


Many amateur astronomers consider it one of the finest northern globular clusters, following only Messier 13.[1] M3 has an apparent magnitude of 6.2,[8] making it a difficult naked eye target even with dark conditions with averted vision. However, with a moderate-sized telescope, the cluster can be seen as a cloudy smudge even in severely light-polluted skies, and can be further defined in darker conditions. It can be found by looking almost exactly halfway along the north-west line that would join Arcturus (α Boötis) to Cor Caroli (α Canum Venaticorum). Using a telescope with a 25 cm (9.8 in) aperture, the cluster has a bright core with a diameter of about 6 arcminutes and spans a total of double that.[1]


This cluster is one of the largest and brightest, and is made up of around 500,000 stars.[10] It is estimated to be 11.4 billion years old.[7] It is centered at 32,600 light-years (10.0 kpc) away from Earth.[12]

Messier 3 is quite isolated as it is 31.6 kly (9.7 kpc) above the Galactic plane and roughly 38.8 kly (11.9 kpc) from the center of the Milky Way. It contains 274 known variable stars, by far the most found in any globular cluster. These include 133 RR Lyrae variables, of which about a third display the Blazhko effect of long-period modulation. The overall abundance of elements other than hydrogen and helium, what astronomers term the metallicity, is in the range of −1.34 to −1.50 dex. This value gives the logarithm of the abundance relative to the Sun; the actual proportion is 3.2–4.6% of the solar abundance. Messier 3 is the prototype for the Oosterhoff type I cluster, which is considered "metal-rich". That is, for a globular cluster, Messier 3 has a relatively high abundance of heavier elements.[13]

Arcturus and Cor Caroli can be used to help locate M3


  1. ^ a b c Thompson, Robert Bruce; Thompson, Barbara Fritchman (2007), Illustrated guide to astronomical wonders, DIY science O'Reilly Series, O'Reilly Media, Inc., p. 137, ISBN 978-0-596-52685-6.
  2. ^ a b Goldsbury, Ryan; et al. (December 2010), "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters", The Astronomical Journal, 140 (6): 1830–1837, arXiv:1008.2755, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830, S2CID 119183070.
  3. ^ Paust, Nathaniel E. Q.; et al. (February 2010), "The ACS Survey of Galactic Globular Clusters. VIII. Effects of Environment on Globular Cluster Global Mass Functions", The Astronomical Journal, 139 (2): 476–491, Bibcode:2010AJ....139..476P, doi:10.1088/0004-6256/139/2/476, hdl:2152/34371, S2CID 120965440.
  4. ^ Delessandro, Emanuele; Schiavon, Ricardo P.; Rood, Robert P.; Ferraro, Francesco R.; Sohn, Sangmo T.; Lanzoni, Barbara; O'Connell, Robert W. (September 2012), "Ultraviolet Properties of Galactic Globular Clusters with Galex. II. Integrated Colors", The Astronomical Journal, 144 (5): 126–139, arXiv:1208.5698, Bibcode:2012AJ....144..126D, doi:10.1088/0004-6256/144/5/126, S2CID 56419886.
  5. ^ Marks, Michael; Kroupa, Pavel (August 2010), "Initial conditions for globular clusters and assembly of the old globular cluster population of the Milky Way", Monthly Notices of the Royal Astronomical Society, 406 (3): 2000–2012, arXiv:1004.2255, Bibcode:2010MNRAS.406.2000M, doi:10.1111/j.1365-2966.2010.16813.x, S2CID 118652005. Mass is from MPD on Table 1.
  6. ^ Brosche, P.; Odenkirchen, M.; Geffert, M. (March 1999). "Instantaneous and average tidal radii of globular clusters". New Astronomy. 4 (2): 133–139. Bibcode:1999NewA....4..133B. doi:10.1016/S1384-1076(99)00014-7.
  7. ^ a b c Forbes, Duncan A.; Bridges, Terry (May 2010), "Accreted versus in situ Milky Way globular clusters", Monthly Notices of the Royal Astronomical Society, 404 (3): 1203–1214, arXiv:1001.4289, Bibcode:2010MNRAS.404.1203F, doi:10.1111/j.1365-2966.2010.16373.x, S2CID 51825384.
  8. ^ a b "M 3". SIMBAD. Centre de données astronomiques de Strasbourg. Retrieved 2006-11-15.{{cite web}}: CS1 maint: postscript (link)
  9. ^ Machholz, Don (2002), The observing guide to the Messier marathon: a handbook and atlas, Cambridge University Press, ISBN 978-0-521-80386-1.
  10. ^ a b Garner, Rob (2017-10-06). "Messier 3". NASA. Retrieved 2018-04-13.
  11. ^ Valcarce, A. A. R.; Catelan, M. (August 2008), "A semi-empirical study of the mass distribution of horizontal branch stars in M 3 (NGC 5272)", Astronomy and Astrophysics, 487 (1): 185–195, arXiv:0805.3161, Bibcode:2008A&A...487..185V, doi:10.1051/0004-6361:20078231, S2CID 11097003.
  12. ^ Cacciari, C.; Corwin, T. M.; Carney, B. W. (January 2005). "A Multicolor and Fourier Study of RR Lyrae Variables in the Globular Cluster NGC 5272 (M3)". The Astronomical Journal. 129 (1): 267–302. doi:10.1086/426325. ISSN 0004-6256. S2CID 8875833.
  13. ^ Cacciari, C.; Corwin, T. M.; Carney, B. W. (January 2005), "A Multicolor and Fourier Study of RR Lyrae Variables in the Globular Cluster NGC 5272 (M3)", The Astronomical Journal, 129 (1): 267–302, arXiv:astro-ph/0409567, Bibcode:2005AJ....129..267C, doi:10.1086/426325, S2CID 8875833.

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