Target: M55 (NGC 6809), class XI, in Sagittarius
Camera: QHY 8 OSC
Scope: GSO CF RC200
EFR: WOF2 reducer f/6.4
Mount: EQ6 Pro
Exposures: 1hr in a mixture of exposures up to 15 minutes captured 16/10/2010 between 9:00 and 11:30pm
Seeing: 50% moon, slight wind, good seeing
Guiding: Orion Starshoot Autoguider using PHD with ED80
Focus: Focus Bahtinov mask
Stacking: DSS with flats and bias, no darks
Processing: PS CS3
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 appearance, that the present author had a star cluster impression even in 7x50 binoculars, where most globular 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.
Nice images Trevor, great star colour but you have got some sort of artifact like a gradient visible around the cluster and another further out. Still a very nice image.
Take your image into Photoshop and turn the brightness up, if you can't see it on your screen, as is. You'll see it. It's an arc extending on the bottom left hand side of the image, as well as behind the glob itself.
