What Is a Solar Eclipse, Anyway?

Mar 25, 2024

On April 8, there will be a total eclipse of the sun visible in some parts of North America, from Mexico through the U.S. and up to Canada. On average, a total solar eclipse happens every 18 months somewhere on earth. The last one visible in North America was seven years ago.

So, what causes this phenomenon? A total eclipse of the sun occurs when the sun, the moon and the earth line up so that the moon appears to cover the sun. A reminder: The sun is the center of our solar system and the earth takes a year to circle around the sun while the moon takes a month to circle around the earth. The earth is also spinning. It takes one day to make a complete rotation. These planetary motions allow eclipses to happen. In fact, eclipses happen on other planets with moons in our solar system.

But how is it that the moon which is about 400 times smaller than the sun can appear to block the sun? The moon is also about 400 times closer to the earth. This causes the moon and sun to appear to be the same size.

When the eclipse reaches totality, the sky darkens and the temperature drops like it does at night. The event takes about 2 hours while the moon slowly covers up the sun. How long the sun is totally blocked by the moon depends on your location—somewhere between 1 and 4 minutes of totality. The sun’s outer atmosphere, called the corona, will suddenly be visible (looks like strings and swirls of light).

While the path of the eclipse is only about 50 miles wide, people outside that range will still experience a partial eclipse. It is important when viewing an eclipse to use protective eyewear—not sunglasses! Paper solar viewers and glasses are available to order on line. When using binoculars or a camera, use a filter. The paper glasses aren’t sufficient. Never look directly at the sun. It only takes seconds for eye damage to occur.