Our Solar System
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17. The tides

Tides simulation
Tides are the periodic rise and fall of the ocean levels. They are caused by the gravitational pull of the Sun and Moon as well as the rotation of the Earth.


The Moon exerts different attraction on different parts of Earth. This is because all parts are not equally distant from the Moon, nor are they all in exactly the same direction from the Moon.

The actual tides we experience are a combination of the larger effect of the Moon and the smaller effect of the Sun. Actual ocean tides are complicated by the additional effects of the Sun and by the shape of the coasts and ocean basins.

When the Sun and Moon are lined up (at new moon or full moon), the tides produced reinforce each other and so are greater than normal. These are called spring tides (the name is connected not to the season but to the idea that higher tides “spring up”).

Spring tides are approximately the same, whether the Sun and Moon are on the same or opposite sides of Earth, because tidal bulges occur on both sides.

When the Moon is at first quarter or last quarter (at right angles to the Sun’s direction), the tides produced by the Sun partially cancel the tides of the Moon, making them lower than usual. These are called neap tides.

Click on the image to run a simulation to better understand this phenomenon.

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