How long does it take the earth to complete one revolution around the sun?
1 Earth year.
A year is
A planet's orbit is quite complex and there are several different ways to describe how long it takes a planet to orbit the Sun. We use the word year to describe the duration of a complete orbit of the Earth around the Sun. A year is about 365.25 days long, but there are four different definitions of a year, each is slightly different in length.
A sidereal year is 365.256363004 days long. It describes the duration of one orbit with respect to the fixed stars.
The vernal equinox is the moment in time when the Sun crosses the equator heading north which occurs around 20 March.
A tropical year is 365.24219 days and is the time from one vernal equinox to the next.
A calendar year is 365.2425 days where the .2425 fraction is because of leap years and leap centuries.
An anomalistic year is 365.259636 days and is the time from perihelion to perihelion.
The reason for the difference in the year lengths of the different years is due to the fact that the Earth's orbit is constantly changing due to precession and the gravitational pull of the other planets.
In fact none of the planets orbit around the Sun. Actually the Sun and all of the planets orbit around the centre of mass of the solar system which is constantly moving and usually above the Sun's surface.
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