When we look at the world around us we are seeing visible light waves (or visible radiation). However, there are many other forms of radiation that we cannot see with our eyes. These types include gamma rays, x-rays, ultraviolet, infrared, microwaves and radio waves. Together with visible light, all these types of radiation make up what we call the electromagnetic spectrum - the complete spectrum of radiation. Light (or radiation) is made up of vibrating waves of electrical and magnetic fields. This is where the term electromagnetic radiation comes from. Electromagnetic radiation travels in waves which have different wavelengths, energies and frequencies.

Wavelength and Frequency

The wavelength is the distance between individual waves (e.g., from one peak to another). The wavelengths of visible light range between 400 to 700 billionths of a meter. But the entire electromagnetic spectrum extends from one billionth of a meter (for gamma rays) to meters (for some radio waves). The frequency is the number of waves which pass a point in space each second. Visible light frequencies range between 430 trillion waves per second (red) and 750 trillion waves per second (violet). The entire electromagnetic spectrum has frequencies between less than 1 billion waves per second (radio) and greater than 3 billion billion waves per second (gamma rays). Light waves are waves of energy and the amount of energy in a wave is proportional to its frequency. Wavelength increases, while frequency and energy decrease, as we go from gamma rays to radio waves.

All electromagnetic radiation travels at the speed of light (186,000 miles or 300,000,000 meters per second in a vacuum). Objects in space send out electromagnetic radiation at all wavelengths - from gamma rays to radio waves. Each type of radiation (or light) brings us unique information so, to get a complete picture of the Universe, we need to study it in all of its light, using each part of the electromagnetic spectrum! Almost everything we know about the Universe comes from the study of the electromagnetic radiation emitted or reflected by objects in space.