Fig. 1

Variation in tide heights during a lunar month. Spring tides occur shortly after new and full moon, twice during a lunar month. During spring tides the Sun and Moon are aligned and their combined gravitational forces lead to the largest difference between high and low tide resulting in particularly high water lines at high tides. In contrast, neap tides occur shortly after the first and third quarter of the Moon. During neap tides, the gravitational forces are at minimum leading to the smallest difference between high and low tide