- Perihelion is the point in the Earth's orbit where it is nearest to the Sun. This generally occurs around January 3rd each year. - Aphelion is the point in the Earth's orbit where it is farthest from the Sun. This generally occurs around July 4th each year. - The slight eccentricity of the Earth's orbit causes this variation in distance, although it is not the primary reason for the seasons (axial tilt is).