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Sizes and Distances: The Earth-Moon-Sun System

Just how big, and how far, are the Sun and Moon? Compare their sizes and distances, and discover the 400x coincidence behind total solar eclipses.

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What you'll cover

How big, how far? 🌍

The Earth, Moon and Sun are wildly different in **size** and **distance**, yet the Sun and Moon look almost the same size in our sky. This module measures the system and reveals the coincidence that makes **total solar eclipses** possible.

The diameters 🗂️

Learn the approximate diameters (note the powers of ten):

Match each body to its approximate diameter

  • The Sun
  • The Earth
  • The Moon
  • About 1,400,000 km
  • About 12,700 km
  • About 3,500 km

Smallest to largest

An interactive activity.

The distances 📏

Now the distances: - **Earth to Moon**: about 384,000 km. - **Earth to Sun**: about 150,000,000 km (1.5 x 10^8 km), called **1 astronomical unit (AU)**. The Sun is vastly further away than the Moon.

Earth to Sun

An interactive activity.

A 400x coincidence 💡

A remarkable coincidence: the Sun's diameter is about **400 times** the Moon's, and the Sun is also about **400 times further away**. Because both ratios are about 400, the Sun and Moon appear **almost the same size** in our sky, which is why **total solar eclipses** are possible.

How many times bigger?

An interactive activity.

Same size in the sky?

Why do the Sun and Moon look almost the same size from Earth?

  • The Sun is about 400 times bigger but also about 400 times further away
  • They are actually exactly the same size
  • The Moon is really larger than the Sun
  • The Sun is very close to the Earth

True or false

Select the TWO true statements about the Earth-Moon-Sun system.

  • The Sun's diameter is about 1.4 x 10^6 km
  • The Earth is larger than the Moon
  • The Moon is larger than the Sun
  • The Earth-Sun distance is smaller than the Earth-Moon distance

Match each quantity to its value

  • Earth-Moon distance
  • Earth-Sun distance
  • 1 astronomical unit (AU)
  • The Sun's diameter
  • About 384,000 km
  • About 150,000,000 km
  • The mean Earth-Sun distance
  • About 1.4 x 10^6 km

Sizes-and-distances frame

The Sun's diameter is about 1.4 x 10^6 km, far larger than the Earth (_____ km) and the Moon (_____ km). The mean Earth-Sun distance is 1 astronomical _____, about 150 million km. The Sun looks the same size as the Moon because it is about _____ times bigger and 400 times further away.

12,700 3,500 unit 400 1,400,000 384,000 mile 100

Explain the eclipse

An interactive activity.