What ‎is an Eclipse and What Should I Know? | Eclipse Glasses

What are Eclipses?

Eclipse 101

What Is an Eclipse?

An eclipse takes place when one heavenly body such as a moon or planet moves into the shadow of another heavenly body. There are two types of eclipses on Earth: an eclipse of the moon and an eclipse of the sun. The term eclipse is most often used to describe either a solar eclipse, when the Moon's shadow crosses the Earth's surface, or a lunar eclipse, when the Moon moves into the Earth's shadow. However, it can also refer to such events beyond the Earth–Moon system: for example, a planet moving into the shadow cast by one of its moons, a moon passing into the shadow cast by its host planet, or a moon passing into the shadow of another moon. 

Check out our on-demand video to learn more!

If you're planning on viewing the much-anticipated 2024 total solar eclipse in the U.S.—or any upcoming solar eclipse—and you'd like to know more about what solar eclipses are, why they're so amazing, and how to view one, this program is for you. First, we'll cover solar eclipse basics. Then we'll take a deep dive into the 2024 total solar eclipse, including how to plan for the eclipse and how to view it safely.

What Is a Solar Eclipse?

The first fact to understand about solar eclipses is that they occur because of a remarkable cosmic coincidence: the Sun is just about the same apparent size in our sky as the Moon. While the Sun is actually about 400 times larger in diameter than the Moon, the Moon is also about 400 times closer than the Sun. Therefore, the Sun and the Moon appear to be about the same size in our sky.

This single fact explains why we see total solar eclipses - the Moon has an apparent size that just barely covers the Sun completely, yet is not too large that the Sun's atmosphere, its corona, is eclipsed as well. We on Earth occupy a celestial sweet spot to witness this sight.

What Is a Solar Eclipse?

If there are intelligent beings in other solar systems, the odds must be quite low that they would enjoy the same circumstance as we on Earth. So we are the beneficiaries of a wonderful cosmic coincidence.

It was not always so. When the Moon first formed around our Earth over 4 billion years ago, it was much closer to the Earth and appeared much larger in our sky. So total solar eclipses in the early epochs of our Earth did block the Sun but also most of the corona. Over the eons, the Moon is gradually receding from the Earth due to the friction from the tides.

There are three types of solar eclipses:

The first is a total solar eclipse. A total solar eclipse is only visible from a small area on Earth. The people who see the total eclipse are in the center of the moon’s shadow when it hits Earth. The sky becomes very dark, as if it were night. For a total eclipse to take place, the sun, moon and Earth must be in a direct line. This amazing event (total solar eclipse) is what the United States will get to experience on April 8th, 2024. This date can't get here soon enough!

The second type of solar eclipse is a partial solar eclipse. This happens when the sun, moon and Earth are not exactly lined up. The sun appears to have a dark shadow on only a small part of its surface. 

The third type is an annular solar eclipse. An annular eclipse happens when the moon is farthest from Earth. Because the moon is farther away from Earth, it seems smaller. It does not block the entire view of the sun. The moon in front of the sun looks like a dark disk on top of a larger sun-colored disk. This creates what looks like a ring around the moon. An annular solar eclipse will occur on June 10, 2021 and will be visible primarily in northern Canada, in Greenland and in north of Russian Far East, in the northeastern United States and Canada, the sun will be partially eclipsed at sunrise, which will be between 5 and 6 A.M.

During a solar eclipse, the moon casts two shadows on Earth. The first shadow is called the umbra (UM bruh). This shadow gets smaller as it reaches Earth. It is the dark center of the moon’s shadow. The second shadow is called the penumbra (pe NUM bruh). The penumbra gets larger as it reaches Earth. People standing in the penumbra will see a partial eclipse. People standing in the umbra will see a total eclipse.

A video that demonstrates/illustrates a solar eclipse:


Never look directly at the sun: It can permanently damage your eyes! You must use proper Eclipse Glasses to look at any type of solar eclipse.