In 46 B.C., acting on the advice of the astronomer Sosigenes, Julius Caesar fixed the year at 365 ¼ days, giving every fourth year, or leap year, an extra day. But the correction by a whole day every four years was too much, and by the 16th Century the Julian calendar was 13 days behind the solar year. In 1582, Pope Gregory XIII directed that 10 days should be dropped from the calendar. He also directed that three times in every 400 years the leap year arrangement should be omitted, by not counting as leap years the years ending in two nougats unless they are divisible by 400. This arrangement will keep the calendar and solar year together until the year 5,000, when the difference will be one day.