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Table of Contents

Enchanted Learning All About Astronomy

Site Index

Our Solar System							Stars	Glossary	Printables, Worksheets, and Activities
The Sun	The Planets	The Moon	Asteroids	Kuiper Belt	Comets	Meteors		Astronomers

The Moon

General Description	Inside the Moon	Craters	Phases of the Moon	Why Do We See Only One Side of the Moon?	Tides	Activities, Web Links
		Map			Lunar Eclipses

TIDES

Tides are periodic rises and falls of large bodies of water. Tides are caused by the gravitational interaction between the Earth and the Moon. The gravitational attraction of the moon causes the oceans to bulge out in the direction of the moon. Another bulge occurs on the opposite side, since the Earth is also being pulled toward the moon (and away from the water on the far side). Since the earth is rotating while this is happening, two tides occur each day.

Isaac Newton (1642 -1727) was the first person to explain tides scientifically. His explanation of the tides (and many other phenomena) was published in 1686, in the second volume of the Principia.

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The Sun's Interaction with the Tides

Spring Tides
Spring tides are especially strong tides (they do not have anything to do with the season Spring). They occur when the Earth, the Sun, and the Moon are in a line. The gravitational forces of the Moon and the Sun both contribute to the tides. Spring tides occur during the full moon and the new moon.

The eccentricity of the orbit of the moon in this illustration is greatly exaggerated.

The Proxigean Spring Tide is a rare, unusually high tide. This very high tide occurs when the moon is both unusually close to the Earth (at its closest perigee, called the proxigee) and in the New Moon phase (when the Moon is between the Sun and the Earth). The proxigean spring tide occurs at most once every 1.5 years.

Neap Tides
Neap tides are especially weak tides. They occur when the gravitational forces of the Moon and the Sun are perpendicular to one another (with respect to the Earth). Neap tides occur during quarter moons.

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The Earth's Oceans
For information on the Earth's oceans, click here.

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