According to Kepler's First Law of Planetary Motion, all planets, comets and asteroids in our solar system have approximately elliptical orbits. (Any single revolution of a body around the Sun is only approximately elliptical, because the phenomenon known as precession of the perihelion prevents the orbit from being a simple closed curve such as an ellipse.) Thus, they all have a closest and a farthest point from the Sun: a perihelion and an aphelion, known collectively as apsides. Orbital eccentricity measures the flatness (departure from a perfect circle) of the orbit.

Earth comes closest to the Sun every year around January 3. It is farthest from the Sun every year around July 4. (For a table of these dates for various years, see Apsis.)

When Earth is closest to the Sun, it is winter in the northern hemisphere and summer in the southern hemisphere.

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