According to the tropical system of astrology, the Sun enters the sign of Aries when it reaches the March equinox, which occurs on average on March 21 (by design). Because the Earth takes approximately 365.24 days to go around the Sun, the precise time of the equinox is not the same each year, and generally will occur about six hours later from one year to the next until reset by a leap year. February 29 of a leap year causes that year's vernal equinox to fall about eighteen hours earlier—according to the calendar—compared with the previous year. From 1800 to 2050 inclusive the vernal equinox date has (or will) range(d) from March 19 at 22:34 UT1 in 2048 to March 21 at 19:15 UT1 in 1903.