The Electromagnetic Spectrum

Where optical light fits into the EM Spectrum
Credit: NSO

This light that we see is just one small chunk of light which is made by stars. We often call this small range of light, optical, or visible light.

The full range of light is called the electromagnetic spectrum.

As you move through the spectrum we go from low-energy to high energy. At the low energy end of the spectrum we find radio waves. Other types of light which are lower energy than optical light are microwaves and infra-red. Light which is higher energy than optical include ultra-violet light and x-rays. The highest energy type of light is called gamma-ray.

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.

verything 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.

You can read more about the spectrum of light and learn how it is used in astronomy.