Tides in the Earth's oceans are caused primarily by the gravitational pull of the moon and, to a lesser extent, the sun. The moon's gravity creates bulges in the ocean's surface, leading to high tides in areas where the bulge occurs. As the Earth rotates, different areas of the coastline pass through these bulges, creating the cyclic rise and fall of sea levels known as tides. The alignment of the moon and sun affects the magnitude of tides, with spring tides occurring during full and new moons and neap tides during the first and third quarters of the moon.