NGC 6559 - Emission and Reflection Nebulae

NGC 6559 is a star-forming region located at a distance of about 5000 light-years from Earth, in the constellation of Sagittarius, showing both emission (red) and reflection (bluish) regions. But NGC 6559 is not just made out of hydrogen gas. It also contains solid particles of dust, made of heavier elements, such as carbon, iron or silicon. The bluish patch next to the red emission nebula shows the light from the recently formed stars being scattered — reflected in many different directions — by the microscopic particles in the nebula. Known as a reflection nebula, this type of object usually appears blue because the scattering is more efficient for these shorter wavelengths of light.