1637 ( MDCXXXVII ) was a common year starting on Thursday of the Gregorian calendar ?and a common year starting on Sunday of the Julian calendar , the 1637th year of the Common Era (CE) and Anno Domini (AD) designations, the 637th year of the 2nd?millennium , the 37th year of the 17th?century , and the 8th year of the 1630s decade. As of the start of 1637, the Gregorian calendar was 10 days ahead of the Julian calendar, which remained in localized use until 1923.