(via APOD: 2012 September 27 - Stars and Dust Across Corona Australis)
Stars and Dust Across Corona Australis
Image Credit & Copyright: Marco Lorenzi (Glittering Lights)
Corona Australis is the Southern Crown. (Here in the northern hemisphere, we have Bootes holding Corona Borealis in the night sky. Bootes, the herdsman, is the constellation that Arcturus is in. Remember “arc to Arcturus and spike to Spica”. Spica is in Virgo.)
In any case, there’s a crown in the skies of the southern hemisphere too, and that’s where you can see this interesting collection of dust, along with a globular cluster…at least in the same line of sight.
The blue light you see in the nebulae is from the stars embedded in the dust, and is being reflected back toward us. Blue light scatters more readily in the dust of the interstellar medium, so more blue than red is being bounced off the “grains” (think something the size of soot) back at us.
The dark areas are where the dust is so thick between our point of view and the star field that we can’t see through it in visible wavelengths. An infrared image would see through it, and into it, to see what’s going on.
The cloud of dust creating this nebular complex is about 500 light-years away, but the globular cluster in the upper left of the image, while appearing close, is actually about 30,000 light-years away, far beyond the dust and stars of the nebulae. They’re very old, gravitationally bound collections of stars that orbit the galaxy, but not necessarily in the galactic plane. This one is NGC 6729.