Solar eclipses | The Earth-sun-moon system | Middle school Earth and space science | Khan Academy
Have you ever been minding your own business, enjoying the sun, when someone steps in front of you and blocks your sunlight? This is pretty much what happens during a solar eclipse, except on a planetary scale. As Earth revolves around the sun, the moon revolves around Earth too. Once in a while, the sun, the moon, and Earth all line up, so the moon's shadow falls onto Earth, causing a solar eclipse.
During a solar eclipse, the moon blocks the sun's light and energy from reaching part of Earth. So, how does a solar eclipse appear from Earth? Well, if you're standing in the center of the moon's shadow, you'd see the moon appear to completely cover the sun's disk. This is called a total solar eclipse. There are other types of solar eclipses, but we're going to focus on total solar eclipses in this video.
During a total solar eclipse, the outermost layer of the sun's atmosphere, called its corona, is visible. On a non-solar eclipse day, the corona is invisible to us because we can't see past the bright light from the sun's surface. Remember to never stare or look at the sun with your naked eye, binoculars, or a telescope. Looking, even for a few seconds, can cause severe and permanent eye damage.
Just because you can't look directly at the sun doesn't mean that you can't enjoy watching a solar eclipse, though. You can watch the eclipse in action through a pinhole viewer or ultraviolet ray-blocking solar eclipse glasses. If you're in the moon's shadow during a total solar eclipse, you might also notice a drop in temperature. On average, the temperature drops about 5.5 degrees Celsius during a total solar eclipse. This is because the moon blocks solar energy from reaching Earth.
Total solar eclipses last only a few minutes. This is because the moon is always revolving around Earth. As the moon keeps on moving, the sun starts to reappear around the moon, and eventually, the sun returns to its usual round and sunny self. But how is it even possible for the moon to appear to block the sun in the first place? The sun and the moon aren't the same size. In fact, the sun is so big that 64.3 million moons could fit inside of it.
However, coincidentally, the sun is far enough away that the moon and the sun appear to us Earthlings to be the same size in the sky. So, when the moon moves between the sun and Earth during a total solar eclipse, it appears from Earth to cover the disk of the sun almost exactly. Total solar eclipses, like all solar eclipses, happen only during a new moon, which is the only time in the moon's orbit where the moon is located between the sun and Earth.
Solar eclipses don't happen every new moon, though. Most of the time, the moon, Earth, and the sun are not lined up. This is because the plane of the moon's orbit around Earth is at a different angle than the plane of Earth's orbit around the sun. This means that the moon's shadow is usually too high or too low to hit Earth and cause an eclipse.
Total solar eclipses won't be visible from Earth in about 600 million years. This is because the moon's orbit is gradually getting bigger, with the moon moving about four centimeters away from Earth each year. So, one day, the moon will appear to be too small in the sky to entirely block the sun's light. Total solar eclipses take place on Earth every 18 months or so, but sometimes they're only visible from the middle of an ocean or a desert.
If you're curious about when the next total solar eclipse will happen near you, look it up online. Scientists are able to calculate when solar eclipses will happen centuries in advance, so you can start planning far ahead. Personally, I'll need to travel if I want to see a total solar eclipse anytime soon because the next one visible in my hometown is on September 14, 2099.