How we observe the Universe

Astronomers have moved from looking with the naked eye to using telescopes, cameras, computers and telescopes in space that detect every part of the EM spectrum.

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From eyes to telescopes

For thousands of years people observed the sky with the naked eye.
From 1609, Galileo used a telescope, discovering moons orbiting Jupiter.
Larger telescopes collect more light, so they can see fainter and more distant objects, and give more detail.
Photography and then digital cameras recorded images that could be studied later, and computers process huge amounts of data.

Seeing in other wavelengths

Objects in space give out radiation across the whole EM spectrum, not just visible light.
Radio telescopes detect radio waves (the CMB was found with one). Infrared telescopes see through dust clouds. X-ray telescopes detect very hot objects, such as gas around black holes.
Using different wavelengths reveals objects and processes that are invisible in visible light.

Telescopes in space

The atmosphere absorbs many wavelengths (such as X-rays, most ultraviolet and much infrared), so these telescopes must be in space.
In space there is also no distortion from moving air and no light pollution, so images are sharper. The Hubble Space Telescope was launched in 1990.
But space telescopes are very expensive and hard to repair.
Worked example

Explain why an X-ray telescope must be placed in space.

  1. The Earth's atmosphere absorbs X-rays.
  2. So X-rays from space do not reach the ground.

Answer: The atmosphere absorbs X-rays, so they can only be detected from above the atmosphere.

Key idea

Telescopes, photography and computers have transformed astronomy. Telescopes for radio, infrared and X-rays show things that visible light cannot. Space telescopes avoid absorption, distortion and light pollution from the atmosphere, but are expensive.

Quick check

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Extra practice

2 more questions

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  1. Why must gamma-ray telescopes be placed in space?

    1. Gamma rays travel faster in space
    2. The atmosphere absorbs gamma rays
    3. There is no gravity in space
    4. Gamma rays are too bright on Earth
    Show the answer

    Answer: The atmosphere absorbs gamma rays

    Gamma rays from space do not reach the ground.

  2. Why are radio telescopes often built very large?

    1. To make radio waves faster
    2. So they can see in daylight only
    3. Larger dishes collect more radio waves and give more detailed images
    4. Because radio waves are very short
    Show the answer

    Answer: Larger dishes collect more radio waves and give more detailed images

    A bigger collecting area gathers more signal and improves resolution.

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Sources and references

Checked by the GCSE-ready editorial team, 16 October 2026. Last updated 2 October 2026. Spotted a mistake? Tell us and we will fix it.

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