| My Hydrogen Alpha filter passes only a very narrow (3-nanometer) slice, or band, from the red part of the optical spectrum. Each time an electron in an atom changes energy levels, a photon is emitted. The band called hydrogen alpha is where interstellar hydrogen emits light when its electron jumps from a particular energy level to another particular energy level. The aesthetic benefit to amateurs is that light pollution and moonlight do not contain hydrogen alpha emissions. This enables me to make photographs such as this one through light polluted skies (though not through clouds, of course) and without concern for moonlight. There was a bright Moon in the sky when I made this photo. Professionals benefit both technically and aesthetically from the existence of the H-Alpha band. There is little or no black background sky in this photo; all of the dark areas are (vast) clouds of dust that obscure the bright nebula behind them. The dust and nebula together hide the background stars; practically every star that you see is between us and the nebula. NGC 7000 lies at a distance of 1,900 light years in the constellation Cygnus. This was to have been a 90-minute photo; airplanes and a guiding problem ruined three of six 15-minute exposures, so this is a 45-minute exposure rather than the planned 90 minutes. Takahashi FSQ-106, SBIG STL-11000M. Telescope, camera, and guider control with a MacBook Pro running Nebulosity, Pixinsight, and Photoshop. My first photo of NGC 7000, made three years earlier, is on this page. My latest photos of NGC 7000 are narrowband images. |
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