Tuesday 11 December 2018 — ASTROPHOTOGRAPHY
The constellation of Orion dominates winter skies in the Northern Hemisphere. The shape of Orion, the hunter, and the three stars of Orion’s belt, are familiar to anyone who looks around the night sky, but the naked eye has to track along Orion’s sword (hanging from the belt from the Northern Hemisphere) to have any hint of the glories this constellation reveals to any telescope. The faint, small, fuzzy patch is the famous Orion nebula, but there are many extraordinary nebulae here.
Alnitak is one of the three stars in Orion’s belt (the left-most from the norther hemisphere). It’s bright and so its glare can easily overwhelm nearby objects, but a good, dark sky and an excellent wide-field telescope and camera shows the star apparently surrounded by gas and dust. In this image, Alnitak is the very bright star above-centre in the middle. to its left is the flame nebula and tracing the red area downwards shows the horse head: patches of dark gas silhouetted against the glowing hydrogen gas of the nebula, which just happen to make a familiar shape. To give a sense of scale, the middle star of Orion’s belt (Alnilam) is just out of the top of the frame to Alnitak’s right, but its glare can clearly be seen, about half way to the right-hand edge.
There is a lot of gas and dust in this image. As well as the obvious bright areas (where the gas is emitting light), there are more diffuse areas of glowing hydrogen, more or less across the whole image, as well as darker patches of dust. Orion’s Molecular Cloud complex is a relatively nearby region that appears to cover most of the constellation, where stars are currently being formed from a region of space where the raw ingredients have been concentrated. All the nebulae in this image are part of that complex.
The glowing gas is thought to be energised by radiation from Alnitak and the other stars in the image. Hydrogen molecules are excited by receiving energy from powerful starlight, then release their own light as they give up the energy. Cooler regions tend to be more red with hotter gas glowing more orange and red. The flame nebula contains a cluster of very hot, new stars (seen by X-Ray rather than visible light telescopes) which provide a great deal of energy to the nebula.
I made this image with telescope 12 of iTelescope. This is a 106mm f5 refractor sited in Siding Springs Australia and fitted with a large sensor specialist camera. The colour image was made from 4 two-minute exposures each through luminance (plain), red, green and blue filters to capture colour. I processed it in PixInsight software. This is a first attempt at processing this rich data. Rings (called “panda eyes”) are visible around some of the stars and there is some harshness in some of the details. I have a feeling this will be a long-term project.