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Hydrogen-alpha commentary

Submitted by Kevin Jardine on 20 November, 2006 - 09:56

Extremely hot O and B class stars release powerful ultraviolet radiation that can strip the electrons from hydrogen atoms. The resulting ionised hydrogen gas glows at several frequencies, including 6563 angstroms, a reddish colour, which astronomers call hydrogen-alpha (H?). In many cases, hot stars create glowing gas over a wide area. These red patches, called HII regions, can easily be seen in many galaxies and are an important marker of spiral arms.

Three recent hydrogen-alpha surveys using ultra-sensitive CCDs and robotic telescopes have begun to revolutionise our view of the night sky by revealing the true extent of many previously familiar Milky Way nebulae. These surveys are WHAM, VTSS and SHASSA.

Nebulosity, it turns out, is almost everywhere and our ability to detect even the faintest traces now shows the amazing size and complexity of these vast clouds of ionised hydrogen.

Douglas Finkbeiner has provided an invaluable service by carefully stitching together the results of these surveys to provide an all-sky hydrogen-alpha image. On the following pages, I have overlaid the Sharpless, Gum, RCW and other nebulae coordinates in the Galaxy Map database on top of this hydrogen-alpha image to provide more information about the true extent and relationships between these nebulae.

This section is an early draft of a hydrogen-alpha commentary (that is, it is unfinished and needs quite a bit of editing). It is best viewed on a monitor with a resolution of 1280x1024 or higher. My intention is to improve the writing and reduce the size of the images at some point in the future.