Nebulae are enormous cosmic clouds of dust or gas. Astronomers often modify the colours in their photographs of nebulae to facilitate their analysis, but producing amazing images in the process.
Here are some photos of nebulae, courtesy of NASA.
Look at the stars! look, look up at the skies!
O look at all the fire-folk sitting in the air!
The bright boroughs, the circle-citadels there!”
Gerard Manley Hopkins, "God's Grandeur"