Open star cluster M18
Open star cluster M18 is in the constellation Sagittarius (Sgr).
Equatorial coordinates (epoch J2000):
Ra 18h 19.9m, Dec -17° 08'
Visual magnitude: 8,0m
Distance to the star clusters M18 to the Sun is 4220 light years
Angular size: 5'
External dimensions the star clusters M18 are about 6 light years.
Number of stars: 40
Age of the object M18 is 50x106 years
Discoverer: Charles Messier, 1764 year.
The designation M18 in other catalogs: NGC 6613
Optimum magnification for a telescope with observations of M18, depending on the aperture of the telescope (D), is about D/3-D/2. 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 M18 is July.
For observers in the northern latitudes:
The nights in July are still quite light, so it makes sense to try to observe M18 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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