1580 (MDLXXX) was a leap year starting on Friday of the Julian calendar, the 1580th year of the Common Era (CE) and Anno Domini (AD) designations, the 580th year of the 2nd millennium, the 80th year of the 16th century, and the 1st year of the 1580s decade. As of the start of 1580, the Gregorian calendar was 10 days ahead of the Julian calendar, which was the dominant calendar of the time.