Book 8, Question 32
Why Are There Two High Tides a Day, Not One?
Most coasts get two high tides a day because Earth spins through two bulges of ocean water every lunar day.
Most coasts get two high tides a day because the Moon stretches the ocean into two bulges! The Moon pulls hardest on the nearest ocean, less on Earth, and least on the far ocean. That stretches the sea into two bulges.
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Quick answers
How long is a lunar day?
A lunar day lasts 24 hours and 50 minutes, so high tide comes a little later each day.
Do all places get two tides?
Some places have only one high tide and one low tide each day.
Sources: NOAA Ocean Service, NOAA Ocean Service
More fun facts
- Earth spins through two bulges of ocean water every lunar day, so most coasts get two high tides and two low tides.
- A lunar day lasts 24 hours and 50 minutes, so high tide comes a little later each day.
- Some places have only one high tide and one low tide each day.
- Most coasts have two high tides a day that are not the same height.
- If Earth were a perfect ball with no big continents, every place would get two equal high tides a day.
Sources: NOAA Ocean Service, NOAA Ocean Service
Questions kids ask
Does every beach have two high tides a day?
Most do, but some places have only one high and one low tide each day.