Rho Ophiuchi nebulae. Optical image of nebulosity in the region of the star Rho Ophiuchi (upper centre). North is at top. This star is swathed in blue nebulosity, the reflection nebula IC 4604, in which tiny dust particles reflect the stars' light. The bright star Antares (Alpha Scorpii) is seen at lower centre. To the right of this star is the bright globular cluster M4 (NGC 6121), with the star Sigma Scorpii above it. Sigma Scorpii is surrounded by a red emission nebula, which glows as its gas is excited by the star's radiation. Dark lanes of dust are seen at upper centre, obscuring the light of the dense starfields in this region.