Messier 28

Short description: Globular cluster in the constellation of Sagittarius

Messier 28

Globular cluster Messier 28 in Sagittarius

Observation data (J2000 epoch)
Class| IV[1]
Constellation| Sagittarius
Right ascension|  18h 24m 32.89s[2]
Declination| –24° 52′ 11.4″[2]
Distance| 18.26 ± 0.98 kly (5.6 ± 0.3 kpc)[3]
Apparent magnitude (V)| 6.8[4]
Apparent dimensions (V)| 11′.2[5]
Physical characteristics
Mass| 5.51×105[6] M☉
Radius| 30 ly[7]
VHB| 15.55 ± 0.10[8]
Metallicity| [math]\displaystyle{ \begin{smallmatrix}\left[\ce{Fe}/\ce{H}\right]\end{smallmatrix} }[/math] = –1.32[6] dex
Estimated age| 12.0 Gyr[9]
Notable features| Contains first pulsar discovered in a globular[10]
Other designations| GCl 94, M 28, NGC 6626[2]
See also: Globular cluster, List of globular clusters

Messier 28 or M28, also known as NGC 6626, is a globular cluster of stars in the center-west of Sagittarius. It was discovered by French astronomer Charles Messier in 1764.[11][lower-alpha 1] He briefly described it as a "nebula containing no star... round, seen with difficulty in 3​1⁄2-foot telescope; Diam 2′."[12]

In the sky it is less than a degree to the northwest of the 3rd magnitude star Kaus Borealis (Lambda Sgr). This cluster is faintly visible as a hazy patch with a pair of binoculars[11] and can be readily found in a small telescope with an 8 cm (3.1 in) aperture, showing as a nebulous feature spanning 11.2 arcminutes. Using an aperture of 15 cm (5.9 in), the core becomes visible and a few distinct stars can be resolved, along the periphery. Larger telescopes will provide greater resolution,[5] one of 25 cm (9.8 in) revealing a dense 2′ core, with more density within.[11]

It is about 18,300 light-years away from Earth.[3] It is about 551000 M☉[6] and its metallicity (averaging −1.32 which means more than 10 times less than our own star), coherency and preponderence of older stellar evolution objects, support its dating to very roughly 12 billion years old.[9] 18 RR Lyrae type variable stars have been found within.

It bore the first discovery of a millisecond pulsar in a globular cluster - PSR B1821–24. This was using the Lovell Telescope at Jodrell Bank Observatory, England.[10] A total of 11 further of these have since been detected in it with the telescope at Green Bank Observatory, West Virginia. As of 2011, these number the third-most in a cluster tied to the Milky Way, following Terzan 5 and 47 Tucanae.[13]

## Contents

* 1 Gallery
* 2 See also
* 3 References and footnotes
* 3.1 References
* 3.2 Footnotes
* 4 External links

## Gallery

* Messier 28 taken by Hubble.[14]

* 2.5' view of M28 taken by Hubble Space Telescope.

* Messier 28 on 2MASS; wide angle

* Map showing location of M28

## See also

* List of Messier objects

## References and footnotes

### References

1. ↑ Shapley, Harlow; Sawyer, Helen B. (August 1927), "A Classification of Globular Clusters", Harvard College Observatory Bulletin 849 (849): 11–14, Bibcode: 1927BHarO.849...11S.
2. ↑ 2.0 2.1 2.2 "M 28". SIMBAD. Centre de données astronomiques de Strasbourg. http://simbad.u-strasbg.fr/simbad/sim-basic?Ident=M+28.
3. ↑ 3.0 3.1 Oliveira, R. A. P.; Ortolani, S.; Barbuy, B.; Kerber, L. O.; Maia, F. F. S.; Bica, E.; Cassisi, S.; Souza, S. O. et al. (2022). "Precise distances from OGLE-IV member RR Lyrae stars in six bulge globular clusters". Astronomy & Astrophysics 657: A123. doi:10.1051/0004-6361/202141596. Bibcode: 2022A&A...657A.123O.
4. ↑ "Messier 28". https://messier.seds.org/m/m028.html.
5. ↑ 5.0 5.1 Inglis, Mike (2004), Astronomy of the Milky Way: Observer's guide to the northern sky, Patrick Moore's Practical Astronomy Series, 1, Springer, p. 21, ISBN 978-1852337094, Bibcode: 2003amwn.book.....I, https://books.google.com/books?id=y4t_-459RPUC&pg=SA2-PA8.
6. ↑ 6.0 6.1 6.2 Boyles, J. et al. (November 2011), "Young Radio Pulsars in Galactic Globular Clusters", The Astrophysical Journal 742 (1): 51, doi:10.1088/0004-637X/742/1/51, Bibcode: 2011ApJ...742...51B.
7. ↑ From trigonometry: radius = distance × sin( diameter_angle / 2 ) = 30 ly
8. ↑ Testa, Vincenzo et al. (February 2001), "Horizontal-Branch Morphology and Dense Environments: Hubble Space Telescope Observations of Globular Clusters NGC 2298, 5897, 6535, and 6626", The Astronomical Journal 121 (2): 916–934, doi:10.1086/318752, Bibcode: 2001AJ....121..916T
9. ↑ 9.0 9.1 Koleva, M. et al. (April 2008), "Spectroscopic ages and metallicities of stellar populations: validation of full spectrum fitting", Monthly Notices of the Royal Astronomical Society 385 (4): 1998–2010, doi:10.1111/j.1365-2966.2008.12908.x, Bibcode: 2008MNRAS.385.1998K
10. ↑ 10.0 10.1 "JBO - Stars". Jodrell Bank Observatory. http://www.jb.man.ac.uk/tech/lovell/aunstar.html.
11. ↑ 11.0 11.1 11.2 Thompson, Robert Bruce; Thompson, Barbara Fritchman (2007), Illustrated Guide to Astronomical Wonders, Diy Science, O'Reilly Media, Inc., p. 402, ISBN 978-0596526856, https://books.google.com/books?id=ymt9nj_uPhwC&pg=PA402.
12. ↑ Burnham, Robert (1979), Burnham's celestial handbook: an observer's guide to the universe beyond the solar system, Dover books explaining science, 3 (2nd ed.), Dover Publications, p. 1609, ISBN 978-0486236735, https://archive.org/details/burnhamscelestia03burn/page/1609
13. ↑ Bogdanov, Slavko et al. (April 2011), "Chandra X-ray Observations of 12 Millisecond Pulsars in the Globular Cluster M28", The Astrophysical Journal 730 (2): 81, doi:10.1088/0004-637X/730/2/81, Bibcode: 2011ApJ...730...81B
14. ↑ "Nebulous, but no nebula" (in en). https://www.spacetelescope.org/images/potw1910a/.

### Footnotes

1. ↑ On July 27

## External links

* Globular Cluster M28 @ SEDS Messier pages
* Messier 28, Galactic Globular Clusters Database page
*   * Messier 28 on WikiSky: DSS2, SDSS, GALEX, IRAS, Hydrogen α, X-Ray, Astrophoto, Sky Map, Articles and images

Coordinates:  18h 24m 32.89s, −24° 52′ 11.4″

* v
* t
* e

Messier objects

List|

* M1
* M2
* M3
* M4
* M5
* M6
* M7
* M8
* M9
* M10
* M11
* M12
* M13
* M14
* M15
* M16
* M17
* M18
* M19
* M20
* M21
* M22
* M23
* M24
* M25
* M26
* M27
* M28
* M29
* M30
* M31
* M32
* M33
* M34
* M35
* M36
* M37
* M38
* M39
* M40
* M41
* M42
* M43
* M44
* M45
* M46
* M47
* M48
* M49
* M50
* M51
* M52
* M53
* M54
* M55
* M56
* M57
* M58
* M59
* M60
* M61
* M62
* M63
* M64
* M65
* M66
* M67
* M68
* M69
* M70
* M71
* M72
* M73
* M74
* M75
* M76
* M77
* M78
* M79
* M80
* M81
* M82
* M83
* M84
* M85
* M86
* M87
* M88
* M89
* M90
* M91
* M92
* M93
* M94
* M95
* M96
* M97
* M98
* M99
* M100
* M101
* M102
* M103
* Added
* M104
* M105
* M106
* M107
* M108
* M109
* M110

See also|

* Caldwell catalogue
* Catalogue of Nebulae and Clusters of Stars
* Herschel 400 Catalogue
* Index Catalogue
* New General Catalogue
* Revised New General Catalogue

* Book
* Category
* Commons
* Portal

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