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Solar Eclipses

Solar Eclipses

Introduction: A total solar eclipse is perhaps one of the most dramatic astronomical events we may witness during our lifetimes. For a few short minutes during a total solar eclipse, day seems to turn to night. The sky darkens. The air cools. The nighttime stars become visible. It is no wonder people travel around the world to see such a spectacular sight!

A solar eclipse only occurs when the new moon passes between Earth and the Sun and the three are in perfect alignment. Since the Moon's orbit around Earth is slightly tilted compared to Earth's orbit, this alignment doesn't happen every month. However, when perfectly aligned, the Moon covers the Sun and its shadow falls on Earth, blocking our view of the Sun. Interestingly, although the diameter of the Sun is much larger than the diameter of the Moon, from Earth, they appear to be the same size. The Moon is much closer to Earth and is located at the exact distance needed to completely block the Sun during a total eclipse.

The diagram below shows the alignment of the Sun, Moon, and Earth during a solar eclipse.
Solar Eclipse Diagram
diagram not shown to scale

There are three main types of solar eclipses: total, partial, and annular.
  1. Total Solar Eclipses - During a total solar eclipse, the Sun appears to be completely blocked by the Moon. The darkest part of the Moon's shadow, called the umbra, traces a narrow path across Earth. Only those located in the umbra's path will experience a total solar eclipse. The few minutes when the Sun's light is completely blocked is called totality. Total solar eclipses only occur once every year or two.
  2. Partial Solar Eclipses - During a partial solar eclipse, part of the Sun appears to be blocked by the Moon. Partial solar eclipses occur when the larger and less dark part of the Moon's shadow, called the penumbra, falls on Earth. Partial solar eclipses happen at least a couple times a year. The penumbra shadow is larger than the umbra, so partial solar eclipses can be seen from more locations than total solar eclipses.
  3. Annular Solar Eclipses - During annular solar eclipses the Moon is farther from Earth than during a total solar eclipse. It is too small to completely cover the Sun. A ring of sunlight shines around the Moon during an annular solar eclipse.

Caution! Never look directly at the Sun! Looking directly at the Sun can cause permanent damage to your eyes. Normal sunglasses will not protect your eyes! Consider using a simple pinhole camera to enjoy a solar eclipse safely.

Directions for This Lesson: After reading the introduction, answer the practice questions. Then apply what you learned by trying the activity.  


Explore what happens during a solar eclipse by changing variables with this interactive. Be sure to select "Solar Eclipse" before starting. Visit here to find when to watch for the next solar eclipse.

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