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spacerings
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The NASA writeup for this says: "Ultraviolet light heats the edges of the dark cloud, releasing gas into the relatively empty region of surrounding space. There, additional ultraviolet radiation causes the hydrogen gas to glow, which produces the red halo of light seen around the pillar.<br /><br />Then it further explains later: "The color image is constructed from three separate images taken in blue, near-infrared, and hydrogen-alpha filters."<br /><br />So, have they chosen to make the hydrogen look red or is it glowing red in visible light?<br /><br />Cone Nebula: http://store.spaceimages.com/noname16.html