The formula for calculating whether a year is a leap year or not is as follows: if a year can be evenly divided by 4 (such as 2012), then it is a leap year unless it can also be evenly divided by 100 (such as 2100). There is one further exception: if a year can be evenly divided by 400 (such as 2000), then it is a leap year.
Know MoreA day on Earth does not really last 24 hours. It takes 23 hours, 56 minutes and 4.1 seconds for the Earth to make a complete rotation. Because of this, the Earth actually rotates about 365.24 times per year. Adding an extra day every four years helps to synchronize the calendar year with the solar year. If the discrepancy were exactly one quarter of a year, then every four years would be a leap year without variation. Since the difference is 0.24 instead of 0.25, one leap year is skipped three times out of every 400 years. Leap year originated in the 16th century, when people realized that the vernal equinox was falling on March 11 instead of March 21. Pope Gregory XIII adjusted the calendar by moving the date ahead by 11 days and instituted the practice of adding an extra day to the calendar every four years.
Learn more in Time & CalendarsA score means 20 years and can more generally refer to any group of 20 items. The word originates from the Old Norse word "skor" or "notch." It is thought to be related to counting large numbers of sheep using a notch on a stick to represent 20.
Full Answer >Unlike the Gregorian calendar, which counts years infinitely, the traditional Chinese calendar is lunisolar and rotates on a 60-year cycle. This means that the years on a Chinese calendar don't ascend in chronological order, and instead its years are named with words rather than numbers. The year names are based on a combination of one of 10 prefixes, or stems, and one of 12 suffixes, or branches.
Full Answer >The transit of Venus happens every 100 years. The last one was in June 2012, and the next one occurs in 2117. This happens as Venus directly passes between the Earth and the Sun. This once-in-a-lifetime astronomical alignment has been witnessed eight times since the telescope was invented. These eye-witness-accounts occurred in 1631, 1639, 1761, 1769, 1874, 1882 and 2004, and the last was in June 2012.
Full Answer >There are 20 years in a score. The word "score" can be used to mean a set or group of any 20 items, not just years.
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