NGC 1907 — ぎょしゃの散開星団

NGC 1907 is a small, moderately dense open cluster in Auriga, about 4,500 light-years away, notable mostly because it lies only 30 arcminutes southwest of the much brighter and more famous Messier 38. The two clusters are almost always observed in the same field of view, making NGC 1907 an automatic bonus for anyone who looks at M38. They appear physically close but are likely at somewhat different distances — a probable optical association rather than a true gravitationally-bound pair, though the question has been revisited several times in the literature. NGC 1907 is older and more compact than M38, roughly half a billion years old.

Trivially found by anyone looking at M38 — NGC 1907 sits in the same low-power eyepiece, a smaller and more concentrated glow than its famous neighbor. In binoculars the pair is a fine sight, with M38 as the brighter patch and NGC 1907 as a small dim companion to its southwest. A 4-inch telescope at 50-80x frames both clusters together; at 100-150x NGC 1907 resolves into a compact knot of 30 or so stars arranged in an elongated oval. A nice exercise in contrast between the two different cluster ages and populations. Best observed November through March.

Discovered by William Herschel on February 1, 1788. Herschel noted its proximity to M38 but did not speculate on any physical connection. The possibility that NGC 1907 and M38 form a true binary cluster has been revisited several times in the 20th century, most recently with Gaia astrometry, which suggests their motions are too different for them to be bound — they are an optical rather than physical pair. The cluster otherwise has led a quiet observational life in the shadow of its famous Messier neighbor.