One mystery that still haunts the halls of astronomy is why the eighteenth-century French comet hunter Charles Messier did not include the Double Cluster in his famous catalogue. “This splendid object … was certainly known in his day,” Robert Burnham Jr. comments in his Celestial Handbook, “and he included other bright clusters such as the Praesepe and the Pleiades.” So why not the Double Cluster? It’s possible that Messier had a very logical reason to omit it. But first a powerful myth must be dispelled.

The Messier catalogue is not a list of the best or the brightest deep-sky objects in the heavens – a common misconception that is the astronomical equivalent of saying a bat is blind. Just as bats are not blind, Messier’s catalogue is not a manifest of celestial superlatives. But who hasn’t loosely described the Messier objects as the finest in the heavens? In his jacket copy for The Messier Album, for instance, Professor Owen Gingerich encourages readers to “find a telescope and a clear night, and begin the chase of the most spectacular sidereal objects of the northern skies.”

Without question, the Messier catalogue contains some of the most spectacular deep-sky objects visible in small telescopes. But their inclusion is largely circumstantial. Messier never intended to create a list of the most spectacular objects in the heavens. His was a catalogue of “comet masqueraders,” as the late comet discoverer Leslie Peltier called them.