Why are some years ahead?
How long does it take for the Earth to orbit the Sun?
Is it always a leap year every four years?
For most years, February 28 is followed by March 1. But every few years, things don't change! February 29, 2016 is february 29, and after February 28, 2020 we will be on February 29. What's going on?
On Earth, a solar year is usually 365 days. This is the time it takes for the Earth to circle the Sun. The Gregorian calendar was introduced in 1582 , and in order to coincide with the solar year , a year is defined as 365 days.
Long ago, however, clever astronomers discovered that the time it takes for the Earth to orbit the Sun is actually a little longer than 365 days. After precise measurements, they determined that it actually took 365.242 days to circle the sun (365 days, 5 hours, 48 minutes, 46 seconds to be precise).
This means that a year should actually be 365 and a quarter of a day. This is difficult to manage on the calendar, so the ancient Egyptians came up with the idea of merging four quarters of a day into one day and adding a day to the calendar every four years to align the calendar year with the solar year.
The ancient Romans, led by Julius Caesar, adopted the same approach as the Egyptians in developing our modern calendar. In fact, they were the first to designate February 29 as an extra day.
This extra day is called a leap day. The year it occurs is called a leap year because it has 366 days and helps the calendar go up an extra day to keep pace with the Earth's cycle around the sun.
Is all this really necessary? Adding a day every four years now may not seem like a big deal, but it will stack up over time. For example, after a century, the difference between a calendar year and a solar year would be 25 days. This means that the start of the season will be nearly a month later than expected. Leap years help correct this problem and make the calendar realistic.
Unfortunately, the mathematical results are a bit more complicated than just adding a day every four years. Astronomers calculated that the solar year was actually 11 minutes and 14 seconds less than 365 and a quarter of a day. This means that an increase of one day every four years will result in three more days than is necessary for every 400 years.
To solve this problem, the ancient Romans decided to skip 3 leap years every 400 years. The rule they set was that only one out of every four "centuries" was considered a leap year. For example, 1700, 1800, and 1900 are not leap years, but 2000 is.
People born on February 29 are often referred to as leap-day people. Leap-Day people usually celebrate their birthday on February 28 or March 1 of a non-leap year (common year). Some leap-day people take advantage of their special birthdays as they age. For example, an 84-year-old leap-day man might claim that he is only 21 years old because he has only celebrated 21 birthdays (once every four years)!
A leap year is a calendar year in which one day is added (or, in the case of the lunar calendar, an additional month) to keep the calendar year synchronized with an astronomical or seasonal year. [1] Because seasonal and astronomical events do not return over a full number of days, calendars with the same number of days each year change over time relative to the events that should match that year. Deviations can be corrected by inserting an extra day or month in a year. Years that are not leap years are called flat years.
For example, in the Gregorian calendar, each leap year has 366 days instead of 365 days, by extending 2 months to 29 days instead of the normal 28 days. These extra days appear in years that are multiples of 4 (except for years that are not divisible by 400). Similarly, in the lunar Hebrew calendar (Adar Aleph), the 13th month is added seven times out of the twelve lunar months of its ordinary year every 19 years to prevent its calendar year from shifting between seasons. In the Baha'i calendar, leap days are added when needed to ensure that the following year begins with the vernal equinox.
Related knowledge
A leap year is one that there are 366 days in that year, which is one more day than the usual year. Leap years are established to bridge the gap between the 365 days of the year specified by the human calendar and the approximately 365.24219 days of the average year of return. Different calendars have different leap methods. The Julian calendar has 1 leap day every 4 years, and the average 1 year is 365.25 days. The Gregorian calendar has 3 fewer leap days per 400 years, averaging 365.2425 days. The extra day is February 29.
BY: wonderopolis
FY: Amoeba
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