M4 terlihat sangat mencolok, dan termasuk salah satu dari gugus bola yang paling mudah untuk dinemukan, yang terletak hanya 1,3 derajat barat bintang Antares, dengan magnitudo semu 10,8.
↑Shapley, Harlow; Sawyer, Helen B. (1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin (849): 11–14, Bibcode:1927BHarO.849...11S.
12Goldsbury, Ryan; etal. (2010), "The ACS Survey of Galactic Globular Clusters. X. New Determinations of Centers for 65 Clusters", The Astronomical Journal, 140 (6): 1830–1837, Bibcode:2010AJ....140.1830G, doi:10.1088/0004-6256/140/6/1830.
12"M 4 -- Globular Cluster". SIMBAD Astronomical Database. Centre de Données astronomiques de Strasbourg. Diakses tanggal 2010-03-25.
↑Marks, Michael; Kroupa, Pavel (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, Bibcode:2010MNRAS.406.2000M, doi:10.1111/j.1365-2966.2010.16813.x. Mass is from MPD on Table 1.
↑Caputo, F.; Castellani, V.; Quarta, M. L. (1985). "Reddening, distance modulus and age of the globular cluster NGC 6121 (M4) from the properties of RR Lyrae variables". Astronomy and Astrophysics. 143 (1): 8–12. Bibcode:1985A&A...143....8C. Pemeliharaan CS1: Banyak nama: authors list (link)
Wikimedia Commons memiliki media mengenai Messier 4.
![{\displaystyle {\begin{smallmatrix}\left[{\mathrm {Fe} }/{\mathrm {H} }\right]\end{smallmatrix}}}](https://wikimedia.org/api/rest_v1/media/math/render/svg/4c0821bd80891e071c08e7c7ee8e022baedf522c)
