Why do tides happen twice a day in many places?
Quick Answer
The Moon’s gravity pulls on Earth’s oceans unevenly, creating two tidal bulges on opposite sides of the planet. As Earth rotates, many coasts pass through both bulges each day.
The Full Story
The Moon’s gravitational pull is stronger on the side of Earth facing it and slightly weaker on the far side, producing a stretching effect in the oceans. This creates one bulge toward the Moon and another on the opposite side because Earth and the oceans move together around their common center of mass. As Earth rotates, most coastal locations move through these bulges roughly every 12 hours and 25 minutes. The Sun also contributes to tides, especially during spring and neap tides. Local coast shape and seafloor depth can make the pattern more complicated.
Key Facts
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"Why are there two tidal bulges instead of one?"
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