Apparent: 6.5° x 4.5° Actual: approximately 50 light years
The colour variationss within the Rho Ophiuchi Cloud Complex are evident in this image. The blue-grey colours in the northern part derive the bluestar Rho Ophiuchi itself, while the orange hues to the south are produced by the red light of Antares. In the southwest (bottom right) of the image, a globular cluster is visible: this cluster is Messier 4, which lies thousands of light years beyond the nebulae that make up the cloud complex. Imagery provided by Aladin sky atlas
The cloud complex is subdivided into various nebulous structures, and many of these have their own distinct colour due to the individual stars that illuninate them. The northern lobe, IC 4604, surrounds the bluestar Rho Ophiuchi (from which the entire complex takes its name), and so the northern part of the cloud structure has a deep blue colour. The southern lobe extends towards redAntares in Scorpius, and thus the southern section of the complex (Cederblad 132, commonly called the AntaresNebula or the Cloud Nebula) has a rich orange colour. To the west of these main lobes, a lesser patch of nebulosity (Sh2-9) is illuminated by the starAlniyat or Sigma Scorpii, and the hydrogen in this region glows a deep crimson.
Running between the two main nebulae that make up the complex are filaments of material, and the entire area is crossed and patterned by dense dark nebulae (hence the alternative name of the 'Rho OphiuchiDN Complex', where 'DN" stands for 'Dark Nebula'). Two of these absorption nebulae are particularly striking against the coloured backdrop of the complex, Barnard 44 and Barnard 45, which run across the area where the blue and orange nebulae meet. Dark strands are found throughout this region, obscuring the stars of the Milky Way behind them, and these strands are given the name of dark streamers.
Within the material that makes up the cloud complex, new stars are being formed (the oldest of these new stars appears to be approximately one million years old). These faint young stars stand out strongly in infrared light, forming clusters of glowing points within the gas and dust of the surrounding nebulae. Many of these objects represent protostars in the earliest periods of formation, while others are young T Tauristars surrounded by the dense circumstellar discs typical of stars early in their evolution.