Cocoon nebula, IC 5146 (centre left). This emission nebula lies about 4000 light years from Earth in the constellation Cygnus. It is a region of star formation. The hot young stars within the nebula generate sufficiently energetic radiation to ionise the hydrogen gas, which glows red. The bright star appearing in the centre of the nebula was formed about 100,000 years ago. It is thought that this star opened a hole in the gas cloud, allowing the glowing material to flow through and become visible.