A solar eclipse occurs as the moon passes in front of the sun, resulting in the earth falling into the shadow of the moon. This lesson explains how and why solar eclipses occur.
Solar Eclipse Definition
A solar eclipse occurs when the moon passes in front of the sun, blocking it out partially or completely. The eclipse results in parts of the earth being covered in the shadow of the moon.
Before we get into the details of a solar eclipse, it is worth noting that we are in the exact point in history that allows for solar eclipses happen. Millions of years ago, the moon was much closer to the earth and, therefore, appeared large in the sky. Since its formation, the moon has gradually been moving away from Earth. Eventually the moon will be much farther away from Earth and will appear smaller. For this brief time, the moon is just the right distance away so that it appears to be the same size as the sun. It’s this phenomenon that provides us with the beauty of solar eclipses.
The Moon Eclipses the Sun
An eclipse of the Sun happens when the New Moon moves between the Sun and Earth, blocking out the Sun’s rays and casting a shadow on parts of Earth.
The Moon’s shadow is not big enough to engulf the entire planet, so the shadow is always limited to a certain area (see map illustrations below). This area changes during the course of the eclipse because the Moon and Earth are in constant motion: Earth continuously rotates around its axis while it orbits the Sun, and the Moon orbits Earth. This is why solar eclipses seem to travel from one place to another
How It Works
Every year, between two and five solar eclipses occur. When the moon passes in front of the sun, the moon will block the sun’s light toward Earth, causing the moon’s shadow to fall onto Earth. In the direct shadow of the moon, the sky on Earth will darken in what is known as the umbra.
Due to the rate of movement of the sun, the moon, and the earth, the duration of a total solar eclipse never lasts more than 7 minutes and 31 seconds. It takes the moon about one month to orbit the earth, but there is not an eclipse every month. This is because the orbital plane of the moon around the earth is slightly different than the orbital plane of the earth around the sun. Therefore, a solar eclipse only occurs when the moon is in front of the sun AND the orbital planes intersect.
Types of Solar Eclipses
There are 4 different types of solar eclipses. How much of the Sun’s disk is eclipsed, the eclipse magnitude, depends on which part of the Moon’s shadow falls on Earth.
- Partial solar eclipses occur when the Moon only partly obscures the Sun’s disk and casts only its penumbra on Earth.
- Annular solar eclipses take place when the Moon’s disk is not big enough to cover the entire disk of the Sun, and the Sun’s outer edges remain visible to form a ring of fire in the sky. An annular eclipse of the Sun takes place when the Moon is near apogee, and the Moon’s antumbra falls on Earth.
- Total solar eclipses happen when the Moon completely covers the Sun, and it can only take place when the Moon is near perigee, the point of the Moon’s orbit closest to Earth. You can only see a total solar eclipse if you’re in the path where the Moon’s casts its darkest shadow, the umbra.
- Hybrid Solar Eclipses, also known as annular-total eclipses, are the rarest type. They occur when the same eclipse changes from an annular to a total solar eclipse, and/or vice versa, along the eclipse’s path.