The Sunˇs gravitational force still plays an important role in the tide phenomenon. When the three celestial objects are alignedthat is, on the days of the full moon and new moonthe gravitational forces of the Sun and the Moon are combined to produce higher-amplitude tides, which are called spring tides. Conversely, the influences of the Sun and the Moon partially cancel each other out during the middle stages of the lunar cycle (first and last quarters), when the two celestial objects exert perpendicular forces on Earth. At these times there are neap tides, and the tidal swell is weak.