NGC6559, an emission nebula

NGC 6559 |   Some 5,000 light years from Earth, toward the asterism of Sagittarius, lies the emission nebula NGC 6559. Hydrogen gas is responsible for the diffuse red glow, while dark clouds of dust absorb much of the nebula's star light. Smaller dust particles scatter the blue light from the bright stars in the bottom half of the image, creating the beautiful blue and purple reflection nebulosity.

Image credit: John and Christie Connor/Adam Block/NOAO/AURA/NSF