Globular star cluster M55
Globular star cluster M55 is in the constellation Sagittarius (Sgr).
Equatorial coordinates (epoch J2000):
Ra (α):19h40.0m, Dec (δ):-30° 58'
Visual magnitude: 7,0m
Distance from the star clusters M55 to the Sun is 19300 light years
Angular size: 19'
External dimensions the star clusters M55 are about 110 light years.
Estimated weight the star clusters: 250x103 suns
Discoverer: Nicolas-Louis De la Caille, 1751 year.
The designation M55 in other catalogs: NGC 6809
M55 is located too far in the southern hemisphere of the sky and is not visible in the north and in the middle latitudes.
In southern latitudes it is located low above the horizon - observation is hampered by atmospheric distortions. Optimum magnification for a telescope with observations of M55, depending on the aperture of the telescope (D), is about D/6-D/3. Higher magnifications of course add details, but lead to a strong drop in the brightness of the image, making it difficult to observe.
The best month for observing M55 is July. At this time, the object is at midnight near its highest point in the sky, that is, it is less affected by light from the lanterns and atmospheric distortions.
For observers in the northern latitudes:The nights in July are still quite light, so it makes sense to try to observe M55 also in August.
The first half of August is also not very dark, in addition the object will be at midnight not at its highest point,which provides the least exposure and atmospheric distortion. But, the difference is not so noticeable. And already in the second half of August the night sky becomes quite dark for observations (although in September it will more darker).The farther south the place of your observation is located, the earlier the sky will darken - both in time on the clock and on the calendar.