Hydrogen is the most abundant element. It emits a characteristic red light known as H-α.
The image shows the logarithm of H-α intensity derived from a composite of night sky surveys. The x-axis and origin of the map correspond to the plane and centre of the Milky Way, respectively. The Milky Way galaxy may be a serene sight to the naked eye, but it appears a more violent place when seen through an H-α filter.
composite survey data: NASA
R package to read FITS (standard astronomy format): FITSio
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