How long does it take for the earth to revolve around the sun?

1 Answer
May 25, 2017

The time it takes the Earth to complete an orbit around the Sun is one year.

Explanation:

The term year is used to describe the time taken for Earth to complete an orbit around the Sun. There are however several different definitions of a year, all of slightly different length. The reason for this being it depends on the frame of reference the measurement is taken in.

A calendar year is 365.2425 days long. The decimal places are due to the corrections introduced by leap years and leap centuries.

A sidereal year is 365.256363004 days and is one orbit with respect to the fixed stars.

A tropical year is 365.24219 which is the time from one Vernal Equinox to the next.

An anomalistic year is 365.259363 days which is the time from one perihelion to the next. The actual time between two successive perihelions actually varies by several days due to the gravitational effects of the other planets. It is currently between 2 and 4 January.

The calendar year is the one we use every day. It is also close to the length of the tropical year. This is important because the Catholic Church has rules about when Easter occurs. Easter Sunday is the first Sunday after the first full moon after the Vernal Equinox. If the tropical and calendar years get out of sync then Easter starts to get either too early or too late. In 1582, Pope Gregory XIII created the Gregorian calendar by deleting 10 days from the year to make sure that the Vernal Equinox occurs on 20th or 21st march.

It took 200 years for the Gregorian Calendar to be adopted, by which time 11 days had to be removed. Here is the calendar for 1752 showing a curious month of September:

      September 1752
Su Mo Tu We Th Fr Sa
              1   2   14 15  16
 17  18  19  20 21 22 23
 24 25 26 27 28 29 30

For astronomical calculations the variations in the Earth's orbit make it impossible to use the year as a unit of time for accurate calculations. Astronomer use the Julian Date which is the decimal number of days since I January 4713 12:00:00. A day being exactly 86,400 seconds.