The Electromagnetic Spectrum

This light that we see is just one small chunk of light which is made by stars. We often call the small range of wavelengths our eyes can detect, optical, or visible light.

The full range of light is called the electromagnetic spectrum. Optical light only covers a range of wavelengths from around 400 – 700 nanometres. 

As you move through the spectrum from short wavelengths to long wavelengths the frequency of the waves decreases. We go from high-energy to low-energy to high energy. 

At the high-energy end of the spectrum we find gammas-rays,  x-rays and ultra-violet rays. Other types of light which are lower energy than optical light are microwaves and infra-red

Where optical light fits into the EM Spectrum
Credit: Philip Ronan

All light travels at the same speed, known as the speed of light and given the letter c. In space, which is a vacuum (meaning there is no air or gas, or anything...) this speed is 300,000 km/s! Light is the fastest thing in the Universe. Nothing can travel faster, and in astronomy we sometimes use its speed to measure distances. We use the term light year to mean how far light could travel in 1 year.

Everything we know about the Universe comes from looking at all of these types of light. Light is one of the few signals that we get from space. It can travel through vacuum of space where there is no air or even particles. Until 2015 when gravitational waves were found, light was the only thing we could measure from space.