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Precession Definition: Lesson for Kids

Instructor: Shoshana Yarin

Shoshana has taught all grades with an emphasis in science and has a master's degree in science.

The Earth is a great spinning ball. How does it spin over time, and what is the effect? Read this lesson if you would like to learn about precession of the Earth.

Spinning Things

A spinning top
Top

Have you ever spun a top? If it spins fast, it will stay upright for a long time. It will even stay up for a while as it wobbles, but will eventually fall down.

What causes the top to fall? Gravity! So if gravity pulls it down, why does it stay upright at all? Let's take a look, so we can relate it to the precession of the Earth.

A top has an axis, or a pole running through the middle. If it were not exactly in the middle, one side of the top would have more mass than the other and gravity would pull it down. It's similar to a washing machine that can't spin because the clothes inside are uneven.

The upright (or vertical) axis makes all the mass (or weight) equal on all sides so that gravity pulls evenly and it is able to spin. When it slows down enough, the axis is no longer perfectly upright, and gravity eventually gets the better of it.

How does a spinning top relate to the Earth? Let's find out!

Earth's Spin

Earth has an axis at 23.5 degrees.
Earth Axis

Earth is similar to a spinning top because it also spins around an axis. It is an imaginary axis with North and South Poles, but it has the same affect. Earth is not a top spinning on a surface, but it does have the pull of gravity from the sun. If the Earth sat with its axis in the same upright plane as it orbits the sun, it would be a smooth spinning top.

Of course, it is a little more complicated than that. Earth's axis sits at a slight tilt of about 23.5 degrees. That's like a top with a slight wobble. How does that affect us? Read on!

Effects of Earth's Spin

The Earth is fatter than it is tall. Because of that, the gravity from the sun and moon cause torque, or twisting, similar to gravity pulling on a top and making it wobble.

Path of stars around the North Star
Star Path

Does that mean that the North Pole is not always in the same place? From our view here on Earth, no. But from space, the orientation, or direction, of the North Pole changes slightly, just like a wobbling top. If you could trace a line with the axis of a wobbling top it would make a circle. The axis of a non-wobbling top would only make a point.

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Practice:
Precession Definition: Lesson for Kids Quiz

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The _____ from the sun and moon's gravity causes the Earth to wobble on its axis.

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