How high is the sky?


The sky is all around us. When you look up at the sky, it can be blue or grey or sometimes pinky orange, and there may be clouds floating along. You might also see birds or insects flying, or aeroplanes or helicopters! But where does the sky start and where does it end?

When we talk about the ‘sky’, we mean the gases that surround our planet. So, the sky actually starts from the Earth’s surface and it goes all the way up and out into space!

The proper name for the layer of gases wrapped around the Earth is the ‘atmosphere’ and is mostly made up of nitrogen, oxygen and water vapour. You can find out more about air in my answer to what is air made of?.

According to the United States National Aeronautics and Space Administration (NASA), the Earth’s atmosphere is about 60 miles thick and is made up of five layers:

  • The troposphere is the layer just above the Earth’s surface. This is where all of our planet’s weather happens.
  • The next layer, the stratosphere, is a warmer part of the atmosphere because it contains a gas called ozone, which absorbs heat energy from the Sun.
  • Next is the mesosphere, which is cooler and is where many of the meteors that come too close to the Earth get burned up.
  • The next layer is the thermosphere, which is hotter again because it absorbs lost of heat from the Sun.
  • Finally, the exosphere is the outermost layer, where our atmosphere starts to blend into space.

So, while we’re thinking about the sky, can you remember why the sky looks blue? If you look at my post about how to make a rainbow, light waves from the Sun get scattered as they bump into gas molecules and tiny particles in the air. Light waves at the blue end of the rainbow are scattered more than those at the red end because they have shorter wavelengths. Our eyes see the scattered blue light waves and that is why the sky looks blue to us.

At night time, when the Sun is shining on a different part of the Earth to where we live, the sky looks much darker and we are able to see the Moon, stars and other planets out in space.

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