Happy Leap Year!
2020 is a leap year, a 366-day-long year.
Every four years, we add an extra day, February 29, to our calendars.
These extra days – called leap days – help synchronize our human-created
calendars with Earth’s orbit around the sun and the actual passing of
the seasons. Why do we need them? Blame Earth’s orbit around the sun,
which takes approximately 365.25 days. It’s that .25 that creates the
need for a leap year every four years.
During non-leap years, aka common years
– like 2019 – the calendar doesn’t take into account the extra quarter
of a day actually required by Earth to complete a single orbit around
the sun. In essence, the calendar year, which is a human artifact, is
faster than the actual solar year, or year as defined by our planet’s motion through space.
Over time and without correction, the
calendar year would drift away from the solar year and the drift would
add up quickly. For example, without correction the calendar year would
be off by about one day after four years. It’d be off by about 25 days
after 100 years. You can see that, if even more time were to pass
without the leap year as a calendar correction, eventually February
would be a summer month in the Northern Hemisphere.
During leap years, a leap day is added to the calendar to slow down and synchronize the calendar year with the seasons. Leap days were first added to the Julian Calendar in 46 B.C. by Julius Caesar at the advice of Sosigenes, an Alexandrian astronomer.
Celebrating the leap year? Take a moment to thank Christopher Clavius
(1538-1612). This German mathematician and astronomer figured out how
and where to place them in the Gregorian calendar. Image via Wikimedia
Commons.
In 1582, Pope Gregory XIII revised the
Julian calendar by creating the Gregorian calendar with the assistance
of Christopher Clavius, a German mathematician and astronomer. The
Gregorian calendar further
stated that leap days should not be added in
years ending in “00” unless that year is also divisible by 400.
This
additional correction was added to stabilize the calendar over a period
of thousands of years and was necessary because solar years are actually
slightly less than 365.25 days. In fact, a solar year occurs over a
period of 365.2422 days.
Hence, according to the rules set forth in the Gregorian calendar, leap years have occurred or will occur during the following years:
1600 1604 1608 1612 1616 1620 1624 1628
1632 1636 1640 1644 1648 1652 1656 1660 1664 1668 1672 1676 1680 1684
1688 1692 1696 1704 1708 1712 1716 1720 1724 1728 1732 1736 1740 1744
1748 1752 1756 1760 1764 1768 1772 1776 1780 1784 1788 1792 1796 1804
1808 1812 1816 1820 1824 1828 1832 1836 1840 1844 1848 1852 1856 1860
1864 1868 1872 1876 1880 1884 1888 1892 1896 1904 1908 1912 1916 1920
1924 1928 1932 1936 1940 1944 1948 1952 1956 1960 1964 1968 1972 1976
1980 1984 1988 1992 1996 2000 2004 2008 2012 2016 2020 2024 2028 2032
2036 2040 2044 2048 2052 2056 2060 2064 2068 2072 2076 2080 2084 2088
2092 2096 2104 2108 2112 2116 2120 2124 2128 2132 2136 2140 2144 2148
2152.
Notice that 2000 was a leap year because it is divisible by 400, but that 1900 was not a leap year.
Since 1582, the Gregorian calendar has been
gradually adopted as a “civil” international standard for many
countries around the world.
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