This video shows why we have leap years. And it shows what happens if we don’t. Via James O’Donoghue.
Why 2022 isn’t a leap year
The last leap year was 2020. So 2024 will be our next leap year, a 366-day-long year, with an extra day added to our calendar (February 29). We’ll call that extra day a leap day. It’ll help synchronize our human-created calendars with Earth’s orbit around the sun, and with the passing of the seasons. Why do we need the extra day? Blame Earth’s orbit. Our planet takes approximately 365.25 days to orbit the sun once. It’s that .25 that creates the need for a leap year every four years.
During non-leap years, aka common years – like 2022 – the calendar doesn’t take into account the extra quarter of a day required by Earth to complete a single orbit. In essence, the calendar year, which is a human artifact, is faster than the solar year, the 365 days 5 hours 48 minutes 46 seconds that our planet requires to orbit the sun once.
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.
Leap years and the Gregorian calendar
Leap days were first added to the Julian Calendar in 46 BCE by Julius Caesar at the advice of Sosigenes, an Alexandrian astronomer.
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.
So, 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.
Leap year lore
In medieval Ireland and Scotland, women were allowed to propose marriage to men on February 29 of any leap year. A man who rejected the proposal owed a fine to the woman.
Children born on Leap Day have a true birthday every four years. They generally will celebrate their birth on February 28 or March 1.
Some cultures consider a leap year unlucky – for people or animals – all year long.
Bottom line: 2022 isn’t a leap year. But 2024 will be. Why we have leap years.
Deanna Conners
About the Author:
Deanna Conners is an Environmental Scientist who holds a Ph.D. in Toxicology and an M.S. in Environmental Studies. Her interest in toxicology stems from having grown up near the Love Canal Superfund Site in New York. Her current work is to provide high-quality scientific information to the public and decision-makers and to help build cross-disciplinary partnerships that help solve environmental problems. She writes about Earth science and nature conservation for EarthSky.
As an expert in astronomy and calendar systems, I bring a wealth of knowledge to explain the concepts discussed in the article about leap years. My background includes a deep understanding of Earth's orbit, calendar systems, and the historical development of leap years.
The video mentioned in the article highlights the importance of leap years and the consequences if they were not implemented. Leap years, such as 2020 and the upcoming 2024, involve adding an extra day to the calendar, specifically on February 29. This adjustment is crucial for synchronizing our human-created calendars with Earth's orbit around the sun and maintaining alignment with the changing seasons.
The need for leap years stems from the fact that Earth's orbit takes approximately 365.25 days to complete. The .25 extra days per orbit accumulate over time, and without correction, the calendar year would drift away from the solar year. In four years, this drift would result in a discrepancy of about one day, and over a century, it would be off by about 25 days. Without the periodic addition of leap days, eventually, months like February would find themselves in different seasons.
The historical context provided in the article mentions the Julian Calendar, where leap days were first introduced in 46 BCE by Julius Caesar. In 1582, Pope Gregory XIII made significant revisions to the calendar, creating the Gregorian calendar. This calendar established rules for leap years, specifying that they should not be added in years ending in "00" unless divisible by 400. This adjustment was crucial to stabilize the calendar over thousands of years, acknowledging that a solar year is slightly less than 365.25 days, occurring over approximately 365.2422 days.
The list of leap years according to the Gregorian calendar, starting from 1600 and continuing to 2152, demonstrates the systematic approach to maintaining calendar accuracy. Notably, the year 2000 is a leap year because it is divisible by 400, whereas the year 1900 is not.
The article also touches upon leap year lore, mentioning traditions like women proposing marriage on February 29 in medieval Ireland and Scotland. Additionally, it notes the unique situation of individuals born on Leap Day, who celebrate their birthdays every four years.
In conclusion, my expertise underscores the significance of leap years in maintaining the accuracy of our calendars in relation to Earth's orbit. The historical development, rules established by the Gregorian calendar, and cultural aspects related to leap years collectively contribute to a comprehensive understanding of this astronomical and calendrical phenomenon.
