As I am traveling from Chile to Spain this weekend, I am posting my OOTW contribution a few days early.
Messier 55 is a beautiful globular cluster in Sagittarius. With showpieces like M 7, M 8 and M 22 close by, this globular cluster often gets overlooked. However, I recently observed this cluster again and realized that it really should be on everybody’s standard summer (or winter if in the southern hemisphere) observing list.
First a little history. This is one of the Messier objects that were not discovered by Messier himself. Instead, it was discovered in 1752 by Nicolas Louis de Lacaille from the Cape of Good Hope. While observing there, Lacaille catalogued nearly 10,000 stars and introduced 14 new constellations which have become standard since. He also discovered 42 nebulous objects, one of which later became known as Messier 55.
Messier tried to observe this globular cluster from Paris starting in 1754 but didn’t succeed until 1788 due to the low altitude of the object from Paris. I did manage to observe it from the Netherlands, which lie even further north, so that says something about the poor skies and telescope used. My home made 15 cm Newtonian telescope probably gives a much better image quality than Messier’s telescopes.
Physically Messier 55 is a very normal Milky Way globular cluster of condensation type XI which indicates a very loose globular cluster.
I have observed Messier 55 several times. With my 15 cm telescope I noted in 2007 in Southern France that “it is faintly visible in the finder scope. At 146x individual stars are visible which are surrounded by a large glow. M55 appears similar in size as M22 but fainter”.
Three weeks ago I observed this globular cluster with a 12.5” dobsonian telescope from a dark location in Chile. The globular cluster was near the zenith, which of course helps. I recall seeing an impressive and completely resolved globular cluster even at a very low magnification of 45x.
While observing Messier 55, be sure to check out the globular clusters Arp 2, Terzan 7 and Terzan 8. I could spot all three of them with the 12.5” dob as faint, round and unresolved glows.
As always,
"Give it a go and let us know!
Good luck and great viewing!"
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