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Open star cluster M7
Open star cluster M7 or Ptolemy is in the constellation Scorpius (Sco).
Equatorial coordinates (epoch J2000):
Ra (α):17h53.9m, Dec (δ):-34° 49'
Visual magnitude: 3,3m - this object can be seen with the naked eye.
Distance from the star clusters M7 to the Sun is 980 light years
Angular size: 80'
Class: I,3,m
External dimensions the star clusters M7 are about 23 light years.
Number of stars: 750
Age of the object M7 is 220x106 years
Discoverer: Klaudios Ptolemaios, 130 year.
The designation M7 in other catalogs: NGC 6475
M7 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 M7, depending on the aperture of the telescope (D), is about 15x-30x. 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 M7 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 M7 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.
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