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Messier 28

Globular Cluster M28 (NGC 6626), class IV, in Sagittarius

Right Ascension 18 : 24.5 (h:m)
Declination -24 : 52 (deg:m)
Distance 18.3 (kly)
Visual Brightness 6.8 (mag)
Apparent Dimension 11.2 (arc min)

Discovered 1764 by Charles Messier.

Globular cluster Messier 28 (M28, NGC 6626) is another conspicuous globular cluster in the rich constellation Sagittarius.

At about 18,000 to 19,000 light years distance, M28 with its linear diameter of 60 light years appears considerably smaller and more compressed than its more impressive neighbor, M22. It is slightly elliptical shaped according to H. Shapley. To resolve it into stars, larger instruments are required; it was William Herschel who first described it as a "star cloud".

M28 contains, in addition its only 18 known RR Lyrae variables, a W Virginis variable (Type II, or population II Cepheid) with a period of 17 days, and a second long period variable (Variable # 17, possibly of RV Tauri type, according to Burnham).

M28 was the second globular clusters where a millisecond pulsar was discovered, in 1987 (the first was M4). This one, 1620-26, is spinning around its axis once every 11 milliseconds.

Globular cluster M28 is one of the authentic discoveries of Charles Messier, who cataloged it on July 27, 1764.

  • Historical Observations and Descriptions of M28
  • Amateur images of M28

  • Marco Castellani's data for M 28
  • Christine Clement's Catalog of Variable Stars in M28
  • SIMBAD Data of M28
  • NED Data of M28
  • Publications on M28 (NASA ADS)
  • Observing Reports for M28 (IAAC Netastrocatalog)
  • NGC Online data for M28

    Hartmut Frommert
    Christine Kronberg

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    Last Modification: August 21, 2007