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Messier 55

Globular Cluster M55 (NGC 6809), class XI, in Sagittarius

[m55.jpg]
Right Ascension 19 : 40.0 (h:m)
Declination -30 : 58 (deg:m)
Distance 17.3 (kly)
Visual Brightness 6.3 (mag)
Apparent Dimension 19.0 (arc min)

Discovered 1752 by Nicholas Louis de Lacaille.

Messier 55 (M55, NGC 6809) is a quite large globular cluster (about 19', roughly 2/3 of the Moon's apparent diameter) but has such a loose appearence, that the present author had a star cluster impression even in 7x50 binoculars, where most globulars look like round nebulae: This one appeared very grainy. As it is about 17,300 light years distant, this diameter corresponds to a linear of about 100 light years. M55 has only very few known variables, 5 or 6. The published values for M55's magnitude vary from mag 5 to 7. Its total luminosity may be near 100,000 times that of the Sun.

M55 was originally discovered by Nicholas Louis de Lacaille on June 16, 1752, when he was observing in South Africa, and cataloged by him as Lac I.14. Charles Messier finally found it and cataloged it on July 24, 1778, after having looked in vain as early as 1764: This is a consequence of this object's southern declination.

The present author [hf] can confirm that M55 is most difficult from Southern Germany also, but splendid if you go a bit more southward (it was very impressive e.g. from Northern Greece).

  • Historical Observations and Descriptions of M55
  • More images of M55
  • Amateur images of M55

  • Marco Castellani's data for M 55
  • Christine Clement's Catalog of Variable Stars in M55
  • SIMBAD Data of M55
  • NED data of M55
  • Publications on M55 (NASA ADS)
  • Observing Reports for M55 (IAAC Netastrocatalog)
  • NGC Online data for M55


    Hartmut Frommert
    Christine Kronberg
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    Last Modification: August 30, 2007