Annular Eclipse: The Changing Size of the Moon

An error occurred trying to load this video.

Try refreshing the page, or contact customer support.

Coming up next: How Can We Predict An Eclipse?

You're on a roll. Keep up the good work!

Take Quiz Watch Next Lesson
Your next lesson will play in 10 seconds
  • 0:01 Comparing the Size of…
  • 0:40 The Types of Solar Eclipses
  • 2:05 Why Does an Annular…
  • 3:39 Lesson Summary
Save Save Save

Want to watch this again later?

Log in or sign up to add this lesson to a Custom Course.

Log in or Sign up

Speed Speed

Recommended Lessons and Courses for You

Lesson Transcript
Instructor: Artem Cheprasov
This lesson will explain what an annular eclipse is and why it occurs with respect to the sizes of the Moon, the Sun, and the position of the Moon during its orbit.

Comparing the Size of the Moon and Sun

Did you know that the Moon is about the same size as the Sun? Well, it is, but only when viewed from the Earth. In reality, the Sun is actually about 400 times bigger than the Moon.

But because the bigger Sun is much farther away from us than the Moon, it appears to be as big as our Moon in the sky. This is what allows for a total solar eclipse to occur on Earth in the first place.

However, these sizes are only a rule of thumb as viewed from Earth. This lesson will explain why and how that influences the kind of solar eclipse you can see, namely the annular eclipse.

The Types of Solar Eclipses

There are three different types of solar eclipses. To demonstrate them, get a round piece of black cardboard paper and a flashlight. The paper should be the same diameter as the flashlight's round end, where the light is coming out of.

Turn the flashlight on and turn it towards you, but be careful not to look directly into the flashlight. You are like the Earth, the flashlight is like the Sun, and the round cardboard paper is like the Moon. If you take the cardboard paper and move it slightly over the flashlight's lit end, it will represent a partial solar eclipse.

If you take the piece of paper, the Moon, and move it so it completely covers the flashlight, that's a total solar eclipse. During a solar eclipse, the period in which the Sun's photosphere is entirely hidden by the Moon is known as totality, and the photosphere is the visible surface of the sun. Those are the two types of solar eclipses you have surely heard of before.

But, did you know there's another kind of solar eclipse? It's called the annular eclipse. The annular eclipse is a kind of solar eclipse where the Sun's photosphere is visible around the edge of the Moon as a bright ring.

This is like taking a cardboard circle that is smaller than the diameter of a flashlight and centering it on the flashlight. You'll be able to see a lot of light protruding around the edge of the cardboard.

Why Does an Annular Eclipse Occur?

The answer to why the annular eclipse occurs is pretty interesting. To explain why, you need to know that there's something called the angular diameter, which is the angle that's made by two lines starting at an observer and ending on the opposite sides of an object. The Moon's angular diameter is about half a degree. This angular diameter, or apparent size of the Moon on our sky, will change depending on where the Moon is located in its slightly elliptical orbit.

To unlock this lesson you must be a Member.
Create your account

Register to view this lesson

Are you a student or a teacher?

Unlock Your Education

See for yourself why 30 million people use

Become a member and start learning now.
Become a Member  Back
What teachers are saying about
Try it risk-free for 30 days

Earning College Credit

Did you know… We have over 200 college courses that prepare you to earn credit by exam that is accepted by over 1,500 colleges and universities. You can test out of the first two years of college and save thousands off your degree. Anyone can earn credit-by-exam regardless of age or education level.

To learn more, visit our Earning Credit Page

Transferring credit to the school of your choice

Not sure what college you want to attend yet? has thousands of articles about every imaginable degree, area of study and career path that can help you find the school that's right for you.

Create an account to start this course today
Try it risk-free for 30 days!
Create an account