I understand what high tides and low tides are in the ocean. But what are “spring tides” and “neap tides”?
Ocean tides follow the moon’s pull, but the sun also pulls on Earth’s oceans. Gravity depends on both mass and distance. The sun’s mass is 27 million times greater than that of the moon, but the sun is 390 times farther from Earth than the moon. So, although the sun’s gravity affects earthly tides, the moon’s gravity has more of an effect because of the moon’s nearness to Earth. The influence of the sun on earthly tides is about 45 per cent that of the moon. Still, the pull of both the sun and moon throughout the month determines the varying height of the tides. As the moon moves in its orbit around Earth, the sun and moon either work together – or work at cross purposes – to determine the height of the tides. When the moon is at first quarter or last quarter, it’s located at right angles to the sun. Then the gravity of the sun and moon pull at cross-purposes, and the range between high and low tides is at its least. These are neap tides, and at such times the difference between high a
