Rho Ophiuchi nebulosity, optical image. These coloured regions are clouds of dust and gas surrounding bright stars, lying around 500 light years from Earth. The star Rho Ophiuchi is in the cloud at upper centre, which appears blue as fine dust particles reflect the light of the star. Short-wavelength blue light is scattered more than red. The red region is an emission nebula surrounding the star Sigma Scorpii. Radiation from the star ionises hydrogen gas in the cloud, causing it to glow. The white object at lower centre is globular star cluster M4. The yellow cloud is material shed from, and reflecting the light of, supergiant star Antares (Alpha Scorpii, lower left). Dark regions are dust clouds obscuring the light from behind.