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Catalogue and alternative designations NGC 6522, NGC 6528 and B298 


Type Globular clusters and dark nebula 
Position 18 04 21, -30 02 57
Constellation Sagittarius
Camera and Telescope STXL16200 and 36.8cm RCOS Ritchey Chretien
Focal Ratio F9
Exposure Details This is a simple LRGB image with Luminance = 150 minutes and Red = Green = Blue = 60 minutes. Luminance was unbinned and the colours were binned 2x2
Description NGC 6522 and NGC 6528 are two globular clusters  in a dense star field in Sagittarius. NGC 6522 is the larger at the bottom.  The dark nebula B 298 is visible at the top of the frame to the left of NGC 6528 which is significantly reddened by interstellar absorption. NGC 6522 has the apparent magnitude of 10.5, apparent diameter of 2 arcminutes and is about 25,100 light years distant. It is possibly the oldest cluster in the milky way with an estimated age of 12 billion light years.  NGC 6528 is somewhat fainter at magnitude 10.65. It's 25,800 light years distant.

Also of interest in this field is Baade's window which is an area of sky containing relatively little interstellar dust in the line of sight from our solar system. It is centered on NGC 6522. The astrophysical significance of Baade's window is that it provides a relatively unimpeded view of the galactic centre. This was first recognised by Walter Baade in 1942.