a very large star in the middle of the sky

The Trifid Nebula, or Messier 20 (M20) The blue portion is a reflection nebula in which the stars backlight the gas but lack the ability to ionize it. The red portion is an emission nebula. The radiation from young stars ionizes hydrogen gas creating H II emissions, which glow red. The dark veins are concentrations of stardust and are classified as dark nebulae. The region around the nebula is considered an open star cluster, with the largest star estimated to be 20 solar masses and being surrounded by over 3,000 stars. The nebula is estimated to be 4,100 light years away from us.