How long is a year, exactly?
Answered by Science Channel
  • Science Channel

    Science Channel

  1. A year is based on the time that the Earth orbits the sun one time. During this time, four seasons take place regularly, and plant and animal life also go through yearly cycles. Early man observed the yearly change in seasons and learned which points in the year were good for planting and harvesting. According to "Encyclopedia Britannica," the exact amount of time it takes for one orbit of the Earth is 365.242199 days. When an extra day is added every four years to the end of February, forming a leap year, this brings the average amount of days per year to 365.25, which is pretty close to the above number. To get even closer to that number, it has been calculated that every 100 years is not necessarily a leap year, but each 400 years is. To know if a centurial year is a leap year, see if it can be divided by 400. For example, although 1700, 1800 and 1900 were not leap years, 1600 and 2000 were. This gives each year a total of 365.2425 days.

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