Synodic month, illustration. As the Moon orbits the Earth (centre), the Earth moves in its orbit around the Sun (top). The Earth is here moving to the right, so the Sun appears to be moving to the left. The synodic month is the orbit of the Moon with respect to the line joining the Sun and Earth. This is longer (by 2.2 days) than the sidereal month (the Moon's orbit around the Earth with respect to the stars).