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Messier 53
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Messier 53 (also known as M53 or NGC 5024) is a magnitude +7.7 globular cluster located 58,000 light-years away in the constellation Coma Berenices.
The globular cluster is easy to find in binoculars or a telescope finder about 1° east of the double star Alpha Coma Berenices (42 Com) (A: 5.05 m, B: 5.08 m, both of spectral type F5V).
In an amateur telescope such as a classic 114mm, M53 is partially resolved as a slightly oval object with a large, bright center. The brightest stars of the cluster (red giants) reach magnitude +12.  For a 8-inch telescope, individual stars can be seen in the outer parts of the cluster. Larger telescopes (12-inch and larger) allow for detailed observation of the core of the cluster.
About 1° east of M53 is the globular cluster NGC 5053. The two clusters are probably physically associated with each other.
Messier 53 contains more than 250,000 stars, most of whom are older and redder than the Sun.

The cluster was discovered by German astronomer Johann Elert Bode using a 80 mm (3.1 inch) refractor in Berlin on the 3rd February 1775.
On 26 February 1777 the cluster was rediscovered by Charles Messier and catalogued as Messier 53.

Right Ascension  13h 12m 55.2s, Declination Dec +18° 10' 05"

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NGC 5053



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Hubble spies another globular cluster, but with a secret

Thousands and thousands of brilliant stars make up this globular cluster, Messier 53, captured with crystal clarity in this image from the NASA/ESA Hubble Space Telescope. Bound tightly by gravity, the cluster is roughly spherical and becomes denser towards its heart.

Messier 53
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These enormous sparkling spheres are by no means rare, and over 150 exist in the Milky Way alone, including Messier 53. It lies on the outer edges of the galaxy, where many other globular clusters are found, almost equally distant from both the centre of our galaxy and the Sun. Although they are relatively common, the famous astronomer William Herschel, not at all known for his poetic nature, once described a globular cluster as "one of the most beautiful objects I remember to have seen in the heavens", and it is clear to see why.

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Title: The Blue Straggler population in the globular cluster M53 (NGC5024): a combined HST, LBT, CFHT study
Authors: G. Beccari, B.Lanzoni, F.R. Ferraro, L.Pulone, M.Bellazzini, F.Fusi Pecci, R.T.Rood, E.Giallongo, R.Ragazzoni, A.Grazian, A.Baruffolo, N.Bouche, P.Buschkamp, C.De Santis, E.Diolaiti, A.Di Paola, J.Farinato, A.Fontana, S.Gallozzi, F.Gasparo, G.Gentile, F.Pasian, F.Pedichini, R.Smareglia, R.Speziali, V.Testa, E.Vernet

We used a proper combination of multiband high-resolution and wide field multi-wavelength observations collected at three different telescopes (HST, LBT and CFHT) to probe Blue Straggler Star (BSS) populations in the globular cluster M53. Almost 200 BSS have been identified over the entire cluster extension. The radial distribution of these stars has been found to be bimodal (similarly to that of several other clusters) with a prominent dip at ~60'' (~2 r_c) from the cluster centre. This value turns out to be a factor of two smaller than the radius of avoidance (r_avoid, the radius within which all the stars of ~1.2 M_sun have sunk to the core because of dynamical friction effects in an Hubble time). While in most of the clusters with a bimodal BSS radial distribution, r_avoid has been found to be located in the region of the observed minimum, this is the second case (after NGC6388) where this discrepancy is noted. This evidence suggests that in a few clusters the dynamical friction seems to be somehow less efficient than expected.
We have also used this data base to construct the radial star density profile of the cluster: this is the most extended and accurate radial profile ever published for this cluster, including detailed star counts in the very inner region. The star density profile is reproduced by a standard King Model with an extended core (~25'') and a modest value of the concentration parameter (c=1.58). A deviation from the model is noted in the most external region of the cluster (at r>6.5' from the centre). This feature needs to be further investigated in order to address the possible presence of a tidal tail in this cluster.

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