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Stephen James O'Meara's secret sky: The curious history of M20 and M21

July 2007: The Trifid Nebula, an observing favorite, remains a mystery because no one is sure who discovered it.
Anyone familiar with the original list of nebulae and clusters compiled by 18th-century French comet-hunter Charles Messier has come to associate his 20th catalog entry with the Trifid Nebula (M20). The Trifid is a summer favorite among amateur astronomers, who enjoy seeking out the three main rifts of obscuring dust, which spread from the Trifid's core like roots from a tree.

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