1839 (MDCCCXXXIX) was a common year starting on Tuesday of the Gregorian calendar and a common year starting on Sunday of the Julian calendar, the 1839th year of the Common Era (CE) and Anno Domini (AD) designations, the 839th year of the 2nd millennium, the 39th year of the 19th century, and the 10th and last year of the 1830s decade. As of the start of 1839, the Gregorian calendar was 12 days ahead of the Julian calendar, which remained in localized use until 1923.