Earth Wavelengths (Electromagnetic Spectrum)

- Demonstrate an understanding that the Earth's atmosphere is transparent to visible light, microwaves and some radio waves
- Interpret data on the effect of the Earth's atmosphere on infrared, ultra-violet and X-rays

The light that we see from stars is just one form of observing we can do. 'Invisible' astronomy or 'non-optical' astronomy tells us a lot about space.

Visible light is a form of radiation travelling at a wavelength millionths of a metre wide. The light travels as a wave and the wavelength determines the colour seen.

'Invisible' astronomy is doing the same but at wavelengths that we cannot detect from Earth or see with our eyes. Imagine you switch on an electric fire. Before you see the bars glow you will feel some heat as infrared radiation.

Special observing techniques have been produced in order to study bodies best at different parts of the spectrum as our atmosphere is good at deflecting or blocking these waves, which is a good thing or the rays would kill us!

The atmosphere lets us see visible light and radio waves. It allows in a very small amount of infrared and ultra violet radiation - enough for you to get a sun tan.


Most infrared radiation is blocked by our lower atmosphere by water vapour. We need to fly quite high in airborne observatories or launch space telescopes to view objects in infrared adequately.

Most objects that produce heat are visible in the infrared spectrum.

Infrared lets us detect the presence of chemicals such as water and nitrogen on nearby planets and moons. We can see stars through dust, and infrared allow us to see objects clearer than visible light.

It also allows us to see objects at long distances. The James Webb Space Telescope will let astronomers view the oldest objects in the Universe, and helps us to understand its formation.

Ultra Violet

A very small amount of ultra violet radiation penetrates our atmosphere; plants and life forms rely on it, although large amounts are harmful. The rest is blocked by the atmosphere, and we rely on space telescopes and satellites to observe it.

Ultra violet is useful in spectroscopy to measure the composition of stars, planets, comets and galaxies.


We are familiar with X-rays to look at the inside of our bodies. Many objects in space radiate X-rays. We find it difficult to observe these as our atmosphere blocks the rays, which is good as they are harmful – to see them, we rely on space telescopes and satellites.
We know that most stars emit X-rays. The Sun's corona produces them as well as the remnants of supernova, quasars and galaxies.


See also...

Why are some types of light and radiation visible to us (e.g radio waves) from Earth and not others (e.g. X-rays)?


Electromagnetic Spectrum


Ultra Violet


Space Telescope Links