Why There Actually Are Not 365 Days in a Year?
Did you know that a year is never actually 365 days long?
A tropical year - also called many other things - is approximately 365 days, 5 hours, 48 minutes, and 45 seconds long. This equates to 365.242189 days.
Tropical years are measured from either an equinox or solstice to the next. You can measure from the Vernal or Autumnal equinox, or the Summer and Winter solstices.
In reality, the length of a tropical year is calculated by the amount of time it takes planet Earth to revolve around the Sun. It's not exact because it differs from year to year.
A true tropical year can vary in length up to a half hour.
For example, the year 2027 will last for 365 days, 5 hours and 39 minutes. Whereas the year 2032 will last for 365 days and 6 hours - much longer.
Furthermore, 100% accuracy is not always possible. When calculating the time of a tropical year from start to end, it's common to be off by a few seconds or more.
Are There Other Names for a Tropical Year?
The most common term is "tropical year," but there are many others that refer to the same length of time.
You can also refer to it as a solar year, astronomical year, or equinoctial year.
None of these terms are wrong to use. The term you hear most will depend on where you live geographically.
Leap Days are Necessary to Keep Our Calendar in Sync
Because the Gregorian calendar tops out at 365 days exactly, it would be out of sync with the tropical year if we didn't add a leap day every four years.
The extra day - or leap day - accounts for the added time shaved off an actual tropical year.
We know this because the Julian calendar was out of sync, after being amended with too many leap years. The Julian calendar was replaced with the Gregorian calendar, the one we use today.
What is Terrestrial Time?
What is a Leap Second?
What is a Time Zone?
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