The aphelion is the point in the orbit of a planet or comet where it is farthest from the Sun. The Earth reaches its aphelion when the Northern Hemisphere is experiencing summer. The point in orbit where a planet or comet is nearest to the sun is called the perihelion. The word aphelion derives from the Greek words, apo meaning away, off, apart and Helios (the Greek god of the sun). Earth's aphelion usually occurs sometime around July 4, when it is around 152.12 million kilometres away from the Sun. This is in contrast to perihelion of the Earth, when it is 141.7 million kilometers away from the Sun.