Astronomy

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Video

Materials

• 1 flashlight
• 1 coin

Short explanation

In this demonstration, the flashlight is the Sun, the coin is the Moon and you are Earth. When the Moon is between the Sun and Earth, a solar eclipse occurs.

Long explanation

The Moon orbits Earth, while Earth (with its moon orbiting it) orbits the Sun. This means that the Moon sometimes ends up in between the Sun and Earth. Seen from the Earth, the Moon and the Sun are almost exactly the same size, which means that the Moon then covers the entire Sun in the sky. No direct sunlight reaches Earth's surface and a solar eclipse occurs. You can also think of it as the Moon casting its shadow on Earth.

One might think that a solar eclipse should happen very often, since the Moon makes one orbit around Earth in just 29.5 days. In fact, a solar eclipse would occur once every 29.5 days if the Moon orbited Earth in the same plane as Earth's orbit around the Sun. But the Moon's orbit is inclined 5 degrees relative to Earth's orbit around the Sun. Therefore, Earth, the Moon and the Sun only end up in line with each other between two and five times a year. Most of these times there is also no total eclipse, as only part of the Moon passes in front of the Sun. In addition, the Moon's orbit is elliptical ("oval"), which means that it's usually too far away from Earth at these times to cover the entire Sun.

Experiment

You can turn this model and demonstration into an experiment. This will make it a better science project. To do that, try answering one of the following questions. The answer to the question will be your hypothesis. Then test the hypothesis by doing the experiment.

• What happens to solar eclipses if the Moon's distance to Earth changes?
• What happens to solar eclipses if the Moon's size changes?
• What happens to solar eclipses if the Sun's size changes?

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