Narrowband data acquisition of the Omega Nebula acquired over 2 nights from eastern Melbourne. The shape of this nebula is like the Greek letter Omega, hence its name.

The gaseous nebula from which stars condense are usually identified by measurement of specific radiation emission lines because stars ionize the gases surrounding them and which then emit radiation at specific wavelengths. One of the most common emission lines studied by astronomers is the Hα line. These emission signals are measured with filters placed on a telescope camera that allow very narrow wavelength ranges to pass into the camera. Amateur astro-photographers also use narrowband filters to reduce the polluting brightness of the Moon and to block the ever-increasing light pollution of our night sky, thus revealing in exquisite detail the shape of interstellar gas clouds within our galaxy.

The Omega Nebula in Sagittarius (Messier 17) is an emission nebula also known as the Swan, Checkmark, or Horseshoe Nebula, and is one of the brightest and most massive star-forming regions in our galaxy. This nebula is home to around 800 stars, with another more than a thousand stars in the process of forming in its outer-most regions.

The Omega Nebula also contains an open young star cluster, just a million years old, that comprise around 35 young hot stars that are embedded within and illuminate the bright core of the nebula and in doing so they cause hydrogen, oxygen and sulphur gases to emit specific spectral emission lines of radiation (i.e. to glow) and that are allowed to pass through the narrowband hydrogen, oxygen and sulphur filters in front of the camera.



Rendered in the ‘HOO = RGB’ palette. The image has just 45 minutes of exposure through each of the Hydrogen Alpha and Oxygen III filters. The outer red/pink-tinged gases are dominated by hydrogen gas (Ha) emissions, whilst the inner whiter-tinged gases in the core of the nebula comprise more equal proportions of hydrogen and oxygen emissions, hence the combination of HOO = RGB yields more equivalent Red-Green-Blue signal which shows white when rendered in combination.