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If science weren't around to tell you what it is, would an eclipse scare you?

Ancient people could not predict eclipses and didn't know when one would end or even that it would end. Rituals to persuade the Sun or Moon to return to its normal state were developed. And they worked! The heavens always return to normal after an eclipse.

Solar Eclipses

A solar eclipse occurs when the new Moon passes directly between the Earth and the Sun (Figure below). This casts a shadow on the Earth and blocks Earth’s view of the Sun.

A solar eclipse, not to scale.

A total solar eclipse occurs when the Moon’s shadow completely blocks the Sun (Figure below). When only a portion of the Sun is out of view, it is called a partial solar eclipse.

A solar eclipse shown as a series of photos.

Solar eclipses are rare and usually only last a few minutes because the Moon casts only a small shadow (Figure below).

A BBC video of a solar eclipse is seen here: http://www.youtube.com/watch?v=eOvWioz4PoQ.

The Moon’s shadow in a solar eclipse covers a very small area.

As the Sun is covered by the moon’s shadow, it will actually get cooler outside. Birds may begin to sing, and stars will become visible in the sky. During a solar eclipse, the corona and solar prominences can be seen.

A solar eclipse occurs when the Moon passes between Earth and the Sun in such a way that the Sun is either partially or totally hidden from view. Some people, including some scientists, chase eclipses all over the world to learn or just observe this amazing phenomenon.

See more at http://www.kqed.org/quest/television/eclipse-chasers.

Lunar Eclipse

A lunar eclipse occurs when the full moon moves through Earth’s shadow, which only happens when Earth is between the Moon and the Sun and all three are lined up in the same plane, called the ecliptic (Figure below). In an eclipse, Earth’s shadow has two distinct parts: the umbra and the penumbra. The umbra is the inner, cone-shaped part of the shadow, in which all of the light has been blocked. The penumbra is the outer part of Earth’s shadow where only part of the light is blocked. In the penumbra, the light is dimmed but not totally absent.

A lunar eclipse.

A total lunar eclipse occurs when the Moon travels completely in Earth’s umbra. During a partial lunar eclipse, only a portion of the Moon enters Earth’s umbra. Earth’s shadow is large enough that a lunar eclipse lasts for hours and can be seen by any part of Earth with a view of the Moon at the time of the eclipse (Figure below). A lunar eclipse does not occur every month because Moon's orbit is inclined 5-degrees to Earth's orbit, so the two bodies are not in the same plane every month.

Partial lunar eclipses occur at least twice a year, but total lunar eclipses are less common.

The moon glows with a dull red coloring during a total lunar eclipse, which you can see in this video of a lunar eclipse over Hawaii: http://www.youtube.com/watch?v=2dk--lPAi04

Summary

  • During a solar eclipse, the new Moon passes between Earth and Sun.
  • During a lunar eclipse, the full Moon moves through Earth's shadow.
  • The umbra is the part of the shadow in which light is completely blocked and the penumbra is the part of the shadow that is partially lit.

Practice

Use these resources to answer the questions that follow.

http://www.teachersdomain.org/asset/ess05_vid_totaleclipse/

1. Why do the moon and sun seem to be the same size from Earth?

2. What causes a solar eclipse?

3. What is first contact?

4. What can be seen at totality?

5. How often do solar eclipses occur?

6. What are the phases of the moon?

7. How often do lunar eclipses occur?

8. Describe a lunar eclipse.

9. What is the penumbra?

10. What is the umbra?

11. How long does a lunar eclipse last?

Review

1. What happens during a solar eclipse?

2. What happens during a lunar eclipse?

3. Why do we not see lunar eclipses every month?

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