Earth-Moon System to Scale

The illustration below shows the Earth-Moon system to scale, with the same scale used for size and distance. I’ve seen a physical model of this once, with the Earth and the Moon in opposite corners of a room, and found it striking how far away (relative to its size) the Moon is from the Earth.

Earth-Moon system to scale

The diameter of the Earth is 12742 km, while the diameter of the Moon is 3475 km. So, to draw the Earth-Moon system to scale on a screen, there have to be 3.67 “Earth”-pixels for each “Moon”-pixel. This ratio of 3.67 is actually quite small compared to the ratio of the sizes of other planets and their moons in our solar system. In other words, the Earth has a large moon. The (average) distance between both is 384400 km. This distance translates into 111 “Moon”-pixels between (the center of) both objects.

Showing the Sun-Earth system to scale in the same way is not reasonably possible on this page. The diameter of the Sun is 1391000 km. Hence, there have to be 109 “Sun”-pixels for each “Earth”-pixel, which is manageable. However, since the distance to the Sun is 149597900 km, the distance between the Earth and the Sun to the same scale would be 11741 “Earth”-pixels.

The enormous size of the Sun becomes apparent in the following illustration, which shows the Sun with the Earth-Moon system to the same scale (all sizes and the distance between the Earth and the Moon). Drawn with the Earth in its center, the Sun is so large that it extends beyond the orbit of the Moon.

Sun, Earth, and Moon, all to scale [Sun photo: Thomas Bresson]

I’ve written a practical follow-up article on the Earth-Moon system, which uses a basketball and a tennis ball to represent the Earth and the Moon. You can find more numbers on the Solar System on NASA’s Solar System Exploration site.