The Moon's Orbit

Now, you may be wondering, if a solar eclipse happens when the Moon, the Sun, and Earth align during the new Moon phase, why isn’t there a solar eclipse every month?

The reason that eclipses are relatively rare is because the orbit of the Moon is not on the same plane as Earth’s orbit around the Sun (called the ecliptic plane). The Moon’s orbit is tilted about 5 degrees relative to the ecliptic plane. This means that most of the time, the Moon is above or below the plane of the Sun and Earth. Eclipses only occur when all three objects align, which can only happen when the Moon’s orbit crosses the ecliptic plane.

Eclipses are somewhat rare to see; however, there are actually at least two solar and two lunar eclipses each year that are visible from somewhere on Earth.

Watch this animation to see how the tilt of the Moon’s orbit affects the positions of the Moon, the Sun, and Earth.

Keyboard Shortcut	Action
Space	Pause/Play video playback
Enter	Pause/Play video playback
m	Mute/Unmute video volume
Up and Down arrows	Increase and decrease volume by 10%
Right and Left arrows	Seek forward or backward by 5 seconds
0-9	Fast seek to x% of the video.
f	Enter or exit fullscreen. (Note: To exit fullscreen in flash press the Esc key.
c	Press c to toggle captions on or off

Use Infograph It to label these screenshots of the animated model. Label the models to explain why one results in a solar eclipse and the other does not.

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The Moon's Orbit

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