This image is just part of a fully coloured image that I intend to create later this winter. The bright star is Alnitak, one of the three stars that make up the belt of Orion. The famous Horsehead nebula is evident, with the neighboring Flame Nebula.
This image is from one set of observations with a narrowband filter. This is the emission from the Hydrogen-Alpha line, at a wavelength of 656 nm. Theoretically no other radiation is getting through the filter (although there is some leakage). The filter passband is 6 nm.
The stars emit radiation across a wide frequency band and therefore are emitting at this frequency as well. Therefore the image includes stellar light as well as emission. There may be some amount of reflection of the starlight as well, since the stars are so intense and there is much dust in the neighborhood.
It was colourized using a “toolkit” that made the stars appear white. This whiteness is false – the software took red spots and made them white. All here is red at precisely 656 nm.
As per Wikipedia: ”H-alpha (Hα) is a specific deep-red visible spectral line in the Balmer series with a wavelength of 656.28 nm in air and 656.46 nm in vacuum; it occurs when a hydrogen electron falls from its third to second lowest energy level.”
This image was captured at Lac Teeples with a narrowband Hydrogen-Alpha filter and the ZWO ASI 6200MM camera on October 23. It is a stack of 108 60 second subframes. It is heavily cropped to show only the main areas of interest.
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