Earth's Orbit
The elliptical orbits of the moon around the Earth and the Earth around the Sun have a substantial effect on the the Earth's tides.
Once a month, at perigee, when the moon is closest to the Earth, tide-generating forces are higher than usual, producing above average ranges in the tides. About two weeks later, at apogee, when the moon is farthest from the Earth, the lunar tide-raising force is smaller, and the tidal ranges are less than average.
When the Earth is closest to the Sun (perihelion), around January 2, tidal ranges are enhanced. At aphelion, when the Earth is furthest from the Sun, around July 2, tidal ranges are reduced.
