I was checking out this picture of the Andromeda Galaxy and in the caption you can find “This image was taken with an hydrogen-alpha filter”: what is it? Thanks!
In: Physics
The lyman-alpha emission line occurs when atomic hydrogen relaxes from the first excited state to the ground state, emitting a photon [n(2) -> n(1)], emitting a photon with an energy equal to the gap between the two energy states. This energy gap is equivalent to a photon with a wavelength of 121.6 nm. There is so much atomic hydrogen in the universe that it’s very bright when viewing 121.6 nm, so it is often appropriate to filter 121.6 nm out of the picture to provide contrast and resolve structures.
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