Today the Earth reaches the furthest point in its orbit around the sun. We are about 5m kilometres more distant from our central star than we were in early January.
This happens because Earth’s orbit is mildly elliptical in shape. The point at which Earth is furthest from the sun is known as aphelion, and the precise moment of its occurrence this year is 23.27 BST on 5 July. It may seem illogical to us in the northern hemisphere that we are closer to the sun in mid-winter than we are in the summer, but this is because the tilt of Earth’s axis determines the seasons, not our distance from the sun. During northern summer that hemisphere is tilted sunward, meaning the sun appears higher in the sky, which concentrates the incoming rays.
However, the elliptical shape of Earth’s orbit, known as its eccentricity, changes gradually over hundreds of thousands of years owing to the gravitational influence of the other planets. It has been estimated that Earth’s eccentricity could have been more than three times larger at certain times in the distant past, causing a 24% variation in the strength of the sun’s light at different times of the year. That would have affected the seasons!
