A calendar year is roughly the time the Earth takes to travel once around the Sun — 365 days.
The Earth actually takes 365.24219 days to orbit the Sun. This is called a solar year.
To compensate for the missing 0.242 days, the western calendar adds an extra day in February every fourth (leap) year, but misses out three leap years every four centuries (century years).
Measured by the stars not the Sun, Earth takes 365.25636 days to go round the Sun, because the Sun also moves a little relative to the stars. This is called the sidereal year.
Earth’s perihelion is the day its orbit brings it closest to the Sun, 3 January.
Earth’s aphelion is the day it is furthest from the Sun, 4 July.
The planet with the shortest year is Mercury, which whizzes around the Sun in just 88 days.
The planet with the longest year is Pluto, which takes 249 years to orbit the Sun.
The planet with the year closest to Earth’s in length is Venus, whose year lasts 225 days.
We get our year from the time the Sun takes to return to the same height in the sky at noon.
Our years come from the time the Earth takes to go once round the Sun, so that the Sun appears at the same height in the sky again. But this journey actually takes not an exact number of days but 365 and a fraction. So the calendar gives a year as 365 days, and compensates with leap years and century years.