Why is M40 quite an inconspicuous Double Star?
Messier scanned the region of this object when he was looking for a non-existing nebula reported by the 17th century astronomer Johann Hevelius (who had reported few real and several nonexistent nebulae). He ended up in the assumption that his object M40 (today also known as Winnecke 4) was the binary which Hevelius had erroneously seen as nebulous. It seems however that Hevelius had observed another (nearby) double star, 74 Ursae Maioris.
