Train Your Brain – The Sky Below Us

The Sky Below Us

Physical Astronomy by Daniel Cummings

In this exercise called “The Sky Below Us” you will learn to see the Earth as a giant ball and understand that the Earth is floating in space. This will allow you to see the sky below us.

Go outside on a clear day.

Look down. What do you see?

Your feet. The floor. The ground.

Look up. What do you see?

Trees. Buildings. The blue sky.

Look down again, but this time… imagine that there is a hole through to the other side of the Earth. Imagine that you can see clear through to the other side. Imagine that you can see the sky below at the “bottom” of that hole. If it is daytime where you are then the other side of the Earth is in night… you should even be able to see some stars in the sky below.

A hole in the ground to the other side of the Earth.

Antipodes (an-TIP-ode-ees)- the other side of Earth

Now, imagine somebody thousands of miles away at the “bottom” of that hole on the exact opposite side of the Earth – at the antipodes. They are standing up straight just like you are.

When they look up they see their own sky and when they look down, they see a hole in the ground and they see your sky. Both of you have sky “below” you.

The sky below us - Earth with a hole through to the antipodes

We tend to see up and down as fixed properties of being on the Earth, but as you can tell from this simple exercise, they are not fixed properties – up and down are relative to the nearest gravitational object.

Earth as a ball

Now, close the hole and look down at your feet again. Imagine that when you look down at your feet instead of standing on flat ground you are standing on a soccer ball that is the shape of the Earth. Imagine that you can see the edge of the Earth curling under you – blue oceans, white clouds, green and brown landforms, the icy poles. Imagine what it would look like if the horizon gathered in under your feet and you are standing on top that big ball. Maybe the ball changes size until it is as big as a house or an elephant. Maybe the ball is as small as a tennis ball.

Beyond the ball and below the ball now is all “sky” (let’s imagine the sky stays blue). Behind the blue sky is a field of stars in every direction. If the Sun were to go dark for a time, the sky would go black and the stars would shine intensely all around.

Summary

This exercise should help you envision the sky below us. At the end of this Train your Brain exercise you should be able to imagine the Earth as a giant ball floating in space.

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