|Right Ascension||19 : 40.0 (h:m)
|Declination||-30 : 58 (deg:m)
|Visual Brightness||6.3 (mag)
|Apparent Dimension||19.0 (arc min)
Discovered 1751-52 by Abbe Nicholas Louis de la Caille.
M55 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 18,000 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 Lacaille in 1751-1752 (his Lac I.14), when he was observing in South Africa. Messier finally found it in 1778, having probably looked in vain as early as 1764: This is a consequence of this object's southern declination. The present author 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).
Last Modification: 9 Dec 1999, 22:58 MET