Shadows in space

About this video

On 8 April 2024, in the middle of the day, the sky over parts of Mexico, the United States and Canada went dark. Street lights came on, birds stopped singing and stars came out. A few minutes later the daylight came back. Nothing was wrong with the Sun: something got in its way.

Every ball in space has a shadow. The Earth and the Moon are each lit by the Sun on one side and throw a long shadow into space on the other, pointing away from the Sun. Most of the time those shadows fall on nothing. An eclipse happens when the Sun, the Earth and the Moon line up and one of the shadows falls on the Earth or on the Moon. In a solar eclipse the Moon passes between the Sun and the Earth and its shadow falls on a small part of the Earth. That can only happen at new moon. It works because the Sun is about 400 times wider than the Moon but also about 400 times farther away, so the two look almost exactly the same size. Only look at a solar eclipse through special eclipse glasses.

In a lunar eclipse the Earth passes between the Sun and the Moon, and the Moon moves into the Earth's shadow, which can only happen at full moon. The Moon turns a dark copper red, lit by sunlight bent through the Earth's air: all the sunrises and sunsets on the Earth at once. The Moon's path is tilted about 5 degrees, so most months the shadows miss. A total solar eclipse reaches some place about every year and a half, but any one town about once in a few hundred years. This video goes with the lesson Eclipses in Astronomy Level 1 on Knaph.

Transcript

1. 0:00On the 8th of April 2024, in the middle of the day, the sky over Mexico, the United States and Canada went dark. Street lights came on. Stars came out. Nothing was wrong with the Sun.
2. 0:14Every ball in space throws a shadow, away from the Sun. Most of the time it falls on nothing. An eclipse is when one falls on the Earth or the Moon.
3. 0:26Sometimes the Moon passes exactly between the Sun and the Earth. Its shadow falls on a small part of the Earth, and for people standing there, the Moon covers the Sun. A solar eclipse. The Moon is between us and the Sun only at new moon. And look at it only through special eclipse glasses. Sunglasses are not enough.
4. 0:48The Sun is about 400 times wider than the Moon. But it is also about 400 times farther away. So in the sky, the two look almost exactly the same size.
5. 1:01Sometimes the Earth passes between the Sun and the Moon, and the Moon moves into the Earth's shadow. A lunar eclipse, only at full moon. The Moon turns a dark copper red. A little sunlight reaches it through the Earth's air. It is lit by all the sunrises and sunsets on the Earth at once.
6. 1:22So why not two eclipses every month? Because the Moon's path is tilted, about 5 degrees. Most months the shadows pass a little above or below. Only a few times a year do they line up. One town sees a total solar eclipse about once in a few hundred years.
7. 1:42An eclipse is a shadow. The Moon's on the Earth, or the Earth's on the Moon.