Tides & Lunar Gravity

How the Moon and Sun create tidal bulges on Earth

Tides result from the differential gravitational pull across Earth's diameter. The Moon pulls the near side of Earth more strongly than the center, and the center more than the far side. This creates two tidal bulges: one facing the Moon (direct gravitational pull) and one on the opposite side (where the center is pulled away from the water). As Earth rotates, coastal locations pass through both bulges, experiencing two high tides per day (semidiurnal tide). When Sun and Moon align (new/full moon), their tidal forces add up — producing extra-large spring tides. When they're at 90° (quarter moons), forces partially cancel — producing smaller neap tides. The tidal range varies from ~1 m (open ocean) to >15 m in funnel-shaped bays (Bay of Fundy). Tidal friction is gradually slowing Earth's rotation (~2.3 ms/century) and pushing the Moon farther away (~3.8 cm/year).