Tropical year facts for kids
A tropical year is the time it takes for the Sun to return to the exact same spot in the sky, as seen from Earth. This means it completes a full cycle of seasons. For example, it's the time from one spring equinox to the next. This is the kind of year that most calendars use.
In the year 2000, a tropical year was about 365.24219 days long. Because of this extra bit of a day, our calendar needs to catch up. The Gregorian calendar uses leap days to keep the calendar year in sync with the tropical year. This helps make sure the seasons always happen at roughly the same time each year.
What "Tropical" Means
The word "tropical" comes from the Greek word tropikos. It means "turn".
The tropic of Cancer and tropic of Capricorn are special lines on Earth. They mark the farthest north and south places where the Sun can appear directly overhead. At these lines, the Sun seems to "turn" in its yearly path. Because these "tropics" are linked to the Sun's seasonal movement, the word "tropical" also describes the "tropical year." People in ancient China, India, and Greece were among the first to try and measure the length of this year.
How Long is a Tropical Year?
A tropical year is the time it takes for the Sun to complete one full cycle of seasons. Imagine the Sun starting at a certain point in the sky. A tropical year is how long it takes to come back to that exact same point. This ensures that spring, summer, autumn, and winter always begin around the same dates each year.
The Calendar Year
The Gregorian calendar is the one most of the world uses today. It's designed to stay in line with the average tropical year. This calendar has a cycle that repeats every 400 years. In this 400-year cycle, there are 146,097 days.
If you divide 146,097 by 400, you get 365.2425 days per year. This is very close to the actual length of the average tropical year, which is about 365.2422 days. This small difference is why we need leap days every four years, and sometimes skip them, to keep the calendar accurate.
The Gregorian calendar was created to fix problems with an older calendar, the Julian calendar. By the year 1582, the date of the spring equinox had moved. It used to be around March 21, but it had shifted to about March 11. This shift was a big deal for Christians. They wanted to make sure Easter was celebrated at the correct time. The rules for figuring out Easter's date relied on March 21 being the spring equinox. So, it was important to keep the calendar aligned with the actual equinox.
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