How Does An Eclipse Occur?

Have you ever watched an eclipse? This spectacular phenomenon is like a painting in the sky. It's breathtaking, like watching the mysteries of the sky unfold before you. Well, I like to think of it as a Shadow Puppet Show interwoven with the play of light and shadow, because that's what it is.

Wait a second... what do I mean? 

Let's start with the basics.

What is an Eclipse?

So let's picture the solar system as a group of kids running round in circles or 'orbits'. There is one in the center, holding a torch, surrounded by eight others. Some of these kids have other kids circling them. 

Am I sending you in circles?

Okay, let's break it down. Let's call the child with the torch in the center the 'Sun'. One of the children orbiting the Sun is the 'Earth'. Like the other planets of the solar system, even the Earth has a moon. Except, it doesn't have a fancy name like each of Jupiter's 95 moons. This one's simply the Moon, and let's suppose that is the child orbiting the Earth. 

So when you're going in circles, there's going to be a point in time when the Sun's light is blocked either by the Moon or the Earth. Suppose you come in the way of light. You will cast a shadow. Well, in this case, one of these bodies (Moon/Earth) casts a shadow on the other. 

That is basically what an eclipse is.

The Types

1. SOLAR ECLIPSE

In the image above, you can see, that the Moon comes in between the Sun and the Earth, blocking some light and casting a shadow on the Earth. To us, it would look somewhat like this:

As the Moon is a relatively small body, this is seen in a restricted region. The shadow is divided into 2 parts:

1. The Umbra: The sun is totally blocked so a total eclipse is seen

2. The Penumbra: The sun is partially blocked so a partial eclipse is seen

There's also an Annular Solar Eclipse. Here, the Moon is at the farthest point from the Earth. Being the farthest, from Earth it would also be seen as the smallest. Hence, you would be able to see a ring of sunlight around the moon. 

2. LUNAR ECLIPSE

Here, as the image shows, the Earth moves between the Sun and the Moon. This can only happen when the Moon is on the far side of the Earth, away from the Sun. Here, the view from the sky would look somewhat like this:

Here, what happens is that light that would normally be reflected from the Moon is blocked by the Earth. The Earth's shadow falls on the moon causing a Lunar Eclipse. But why would the Moon appear red? Well, the Earth's atmosphere is like a filter. It removes most of the blue light, hence it makes the Moon appear red. 

Again there are 2 types of this eclipse:

1. Total Lunar Eclipse: the Earth, Sun and Moon are perfectly aligned 

2. Partial Lunar Eclipse: the three bodies are not perfectly aligned, so only part of the Earth's shadow (the umbra: the darker region) is cast on the Moon

There's also a Penumbral Lunar Eclipse where the shadow cast by the Earth is the fainter, lighter region (the penumbra). 

How is this helpful?

Well, for scientists, eclipses help to determine the nature of the Moon's surface - the rougher areas and the flatter regions both.

Conclusion

So next time you look at an eclipse, think what actually must be happening behind the scenes, behind the curtains, in this shadow puppet show.