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Use this resource to read about and take notes on the STEM NIGHT project

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Start at the smallest size in this scale simulation. As you scroll through, note the scale of each wavelength of the EM spectrum. For example, a gamma ray is somewhat smaller than a hydrogen atom. What is the size range for a gamma ray?

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Scale of the Universe: Discover the vast ranges of our visible and invisible world.

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Scale of Universe is an interactive experience to inspire people to learn about the vast ranges of the visible and invisible world.

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How do you discover light that your eyes can't see? Serendipity. In the year 1800, Sir William Herschel was exploring the question of how much heat was contained by the different colors of visible light. He devised and experiment where he used a glass prism to separate sunlight into it's rainbow of colors. Then, he placed a thermometer under each color, with one extra thermometer just beyond the red light of the spectrum. He found that the thermometer that was seemingly out of the light had the highest temperature. Thus, he discovered infrared light.

A year later, Johann Wilhelm Ritter was inspired by Herschel's discovery to see if there might be light just beyond the purple end of the spectrum. Indeed, there was, and Ritter discovered ultraviolet light. In 1867, James Clerk Maxwell predicted that there should be light with even longer wavelengths than infrared light. In 1887 Heinrich Hertz demonstrated the existence of the waves predicted by Maxwell by producing radio waves in his laboratory.

It took a bit longer for scientists to discover the higher-energy (shorter wavelength) light in the electromagnetic spectrum.

X-rays were first observed and documented in 1895 by Wilhelm Conrad Röntgen, a German scientist who found them quite by accident when experimenting with vacuum tubes. A week after he first observed them, he took an X-ray photograph of his wife's hand, which clearly revealed her wedding ring and her bones. The photograph electrified the general public and aroused great scientific interest in the new form of radiation. Röntgen called it "X" to indicate it was an unknown type of radiation. The name stuck, although many of his colleagues suggested calling them Röntgen rays.

While Röntgen first observed the effects of X-rays in 1895, it wasn't until 1912 that scientists were able to conclude that they were, indeed, another form of light."

Gamma-rays were first observed in 1900 by Paul Villard when he was investigating radiation from radium. A few years later, Ernest Rutherford proposed the name "gamma-rays," for this new radiation, and the name stuck. Like X-rays, the exact nature of gamma-rays took a little while for scientists to work out. In 1914, when Rutherford observed that they could be reflected off the layers of a crystal, it was clear that they were akin to X-rays (in other words another form of light), but with much shorter wavelengths.

Updated: September 2013

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How do you discover light that your eyes can't see? Serendipity. In the year 1800, Sir William Herschel was exploring the question of how much heat was contained by the different colors of visible light. He devised and experiment where he used a glass prism to separate sunlight into it's rainbow of colors.

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A NASA site

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The electromagnetic (EM) spectrum is the range of all types of EM radiation. Radiation is energy that travels and spreads out as it goes – the visible light that comes from a lamp in your house and the radio waves that come from a radio station are two types of electromagnetic radiation. The other types of EM radiation that make up the electromagnetic spectrum are microwaves, infrared light, ultraviolet light, X-rays and gamma-rays.

You know more about the electromagnetic spectrum than you may think. The image below shows where you might encounter each portion of the EM spectrum in your day-to-day life.

Is a radio wave the same as a gamma ray?

Are radio waves completely different physical objects than gamma-rays? They are produced in different processes and are detected in different ways, but they are not fundamentally different. Radio waves, gamma-rays, visible light, and all the other parts of the electromagnetic spectrum are electromagnetic radiation.

Electromagnetic radiation can be described in terms of a stream of mass-less particles, called photons, each traveling in a wave-like pattern at the speed of light. Each photon contains a certain amount of energy. The different types of radiation are defined by the the amount of energy found in the photons. Radio waves have photons with low energies, microwave photons have a little more energy than radio waves, infrared photons have still more, then visible, ultraviolet, X-rays, and, the most energetic of all, gamma-rays.

Measuring electromagnetic radiation

Electromagnetic radiation can be expressed in terms of energy, wavelength, or frequency. Frequency is measured in cycles per second, or Hertz. Wavelength is measured in meters. Energy is measured in electron volts. Each of these three quantities for describing EM radiation are related to each other in a precise mathematical way. But why have three ways of describing things, each with a different set of physical units?

The short answer is that scientists don't like to use numbers any bigger or smaller than they have to. It is much easier to say or write "two kilometers" than "two thousand meters." Generally, scientists use whatever units are easiest for the type of EM radiation they work with.

Astronomers who study radio waves tend to use wavelengths or frequencies. Most of the radio part of the EM spectrum falls in the range from about 1 cm to 1 km, which is 30 gigahertz (GHz) to 300 kilohertz (kHz) in frequencies. The radio is a very broad part of the EM spectrum.

Infrared and optical astronomers generally use wavelength. Infrared astronomers use microns (millionths of a meter) for wavelengths, so their part of the EM spectrum falls in the range of 1 to 100 microns. Optical astronomers use both angstroms (0.00000001 cm, or ) and nanometers (0.0000001 cm, or ). Using nanometers, violet, blue, green, yellow, orange, and red light have wavelengths between 400 and 700 nanometers. (This range is just a tiny part of the entire EM spectrum, so the light our eyes can see is just a little fraction of all the EM radiation around us.)

The wavelengths of ultraviolet, X-ray, and gamma-ray regions of the EM spectrum are very small. Instead of using wavelengths, astronomers that study these portions of the EM spectrum usually refer to these photons by their energies, measured in electron volts (eV). Ultraviolet radiation falls in the range from a few electron volts to about 100 eV. X-ray photons have energies in the range 100 eV to 100,000 eV (or 100 keV). Gamma-rays then are all the photons with energies greater than 100 keV.

Show me a chart of the wavelength, frequency, and energy regimes of the spectrum

Why do we put telescopes in orbit?

Most electromagnetic radiation from space is unable to reach the surface of the Earth. Radio frequencies, visible light and some ultraviolet light makes it to sea level. Astronomers can observe some infrared wavelengths by putting telescopes on mountain tops. Balloon experiments can reach 35 km above the surface and can operate for months. Rocket flights can take instruments all the way above the Earth's atmosphere, but only for a few minutes before they fall back to Earth.

For long-term observations, however, it is best to have your detector on an orbiting satellite and get above it all!

Updated: March 2013

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The electromagnetic (EM) spectrum is the range of all types of EM radiation. Radiation is energy that travels and spreads out as it goes - the visible light that comes from a lamp in your house and the radio waves that come from a radio station are two types of electromagnetic radiation.

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by Chris Woodford. Last updated: May 7, 2018.

You might think the world is essentially what you can see in front of you, but think for a moment and you'll realize this isn't true. When you close your eyes, the world doesn't cease to exist just because there's no light to see by. If you were a rattlesnake or an owl, you could see perfectly well by night. Thinking more laterally, what if you were a radar set mounted on an airplane? Then you could help pilots see in darkness or bad weather by detecting reflected radio waves. And if you were a camera sensitive to X rays, you could even see through bodies or buildings! The light we can see is only one part of all the electrical and magnetic energy buzzing around our world. Radio waves, X rays, gamma rays, and microwaves work in a very similar way. All together, this energy is called the electromagnetic spectrum. Let's take a closer look at what that means!

Photo: Water drops bend (or refract) short wavelength blue light more than long-wavelength red light, which is why rainbows arc across the sky when sunlight streams through rain, making a rainbow and revealing the spectrum "hidden" inside white light.

What is electromagnetic radiation?

Light waves and other types of energy that radiate (travel out) from where they're produced are called electromagnetic radiation. Together, they make up what's known as the electromagnetic spectrum. Our eyes can see only a limited part of the electromagnetic spectrum-the colorful rainbow we see on sunny-rainy days, which is an incredibly tiny part of all the electromagnetic radiation that zaps through our world. We call the energy we can see visible light (we discuss it in detail in our main article on light) and, like radio waves, microwaves, and all the rest, it's made up of electromagnetic waves. These are up-and-down, wave-shaped patterns of electricity and magnetism that race along at right angles to one another, at the speed of light (300,000 km per second or 186,000 miles per second, which is fast enough to go 400 times round the world in a minute!). The light we can see stretches in a spectrum from red (the lowest frequency and longest wavelength of light our eyes can register) through orange, yellow, green, blue, and indigo to violet (the highest frequency and shortest wavelength we can see).

Artwork: Above: How an electromagnetic wave travels: If we could peer inside a light ray (or other electromagnetic wave), this is what we'd see: an electrical wave vibrating in one direction (blue in this case, and vibrating up-and-down) and a magnetic wave vibrating at right angles to it (red in this case, and vibrating from side to side). The two waves vibrate in perfect step, at right angles to the direction they're traveling in. This diagram shows us something scientists only really understood in the 19th century: electricity and magnetism are equal partners that work together closely at all times. Below: An animated version of the same artwork.

What kinds of energy make up the electromagnetic spectrum?

What are the other kinds of electromagnetic radiation that objects give off? Here are a few of them, ranged in order from the longest wavelength to the shortest. Note that these are not really definite bands with hard edges: they blur into one another with some overlap between them.

Radio waves: If our eyes could see radio waves, we could (in theory) watchTV programs just by staring at the sky! Well not really, but it's a nice idea. Typical size: 30cm-500m. Radio waves cover a huge band of frequencies, and their wavelengths vary from tens of centimeters for high-frequency waves to hundreds of meters (the length of an athletics track) for lower-frequency ones. That's simply because any electromagnetic wave longer than a microwave is called a radio wave.

Microwaves: Obviously used for cooking in microwave ovens, but also for transmitting information in radar equipment. Microwaves are like short-wavelength radio waves. Typical size: 15cm (the length of a pencil).

Infrared: Just beyond the reddest light we can see, with a slightly shorter frequency, there's a kind of invisible "hot light" called infrared. Although we can't see it, we can feel it warming our skin when it hits our face-it's what we think of as radiated heat. If, like rattlesnakes, we could see infrared radiation, it would be a bit like havingnight-vision lenses built into our heads. Typical size: 0.01mm (the length of a cell).

Visible light: The light we can actually see is just a tiny slice in the middle of the spectrum.

Ultraviolet: This is a kind of blue-ish light just beyond the highest-frequency violet light our eyes can detect. The Sun transmits powerful ultraviolet radiation that we can't see: that's why you can get sunburned even when you're swimming in the sea or on cloudy days-and why sunscreen is so important. Typical size: 500 nanometers (the width of a typical bacteria).

X rays: A very useful type of high-energy wave widely used in medicine and security. Find out more in our main article on X rays. Typical size: 0.1 nanometers (the width of an atom).

Gamma rays: These are the most energetic and dangerous form of electromagnetic waves. Gamma rays are a type of harmful radiation. Typical size: 0.000001 nanometers (the width of an atomic nucleus).

The electromagnetic spectrum

Photo: Diagram of electromagnetic spectrum courtesy of NASA.

All the different kinds of electromagnetic radiation are essentially the same "stuff" as light: they're forms of energy that travel in straight lines, at the speed of light (300,000 km or 186,000 miles per second), when electrical and magnetic vibrations wiggle from side to side. Together, we refer to these forms of energy as the electromagnetic spectrum. You can think of it as a kind of super-big spectrum that stretches either side of the smaller spectrum we can actually see (the rainbow of light colors).

There are lots of images of the electromagnetic spectrum available online, so we won't bothering drawing it out for you again. Click the small image on the right to see quite a nice diagram of the spectrum from NASA.

Who discovered the electromagnetic spectrum?

Photo: James Clerk Maxwell: the father of electromagnetism. Photo courtesy of Wikimedia Commons.

Up until the 19th century, scientists thought electricity and magnetism were completely separate things. Then, following a series of amazing experiments, it became clear that they were linked together very closely. Electricity could cause magnetism and vice-versa! Around 1819/1820, a Danish physicist called Hans Christian Oersted (1777-1851) showed that an electric wire would create a pattern of magnetism around it. About a decade later, English chemist Michael Faraday (1791-1867) proved that the opposite could happen too-you could use magnetism to generate electricity-and that led him to develop the electric motors and electricity generators that now power our world.

Thanks to the pioneering work of people like this, another great scientist, James Clerk Maxwell (1831-1879) was able to come up with a single theory that explained both electricity and magnetism. Maxwell summed up everything people had discovered in four simple equations to produce a superb theory of electromagnetism, which he published in 1873. He realized that electromagnetism could travel in the form of waves, at the speed of light, and concluded that light itself had to be a kind of electromagnetic wave. About a decade after Maxwell's death, a brilliant German physicist named Heinrich Hertz (1857-1894) became the first person to produce electromagnetic waves in a laboratory. That piece of work led to the development of radio, television, and-much more recently-things like wireless Internet.

How can we "see" other parts of the spectrum?

Our eyes pick up light from just one tiny slice of the spectrum, but the Universe is buzzing with other kinds of radiation. If we want to "see" beyond the electromagnetic limits of our own eyes, we can use telescopes "tuned" to higher or lower wavelengths. Astronomers use all kinds of telescopes-some on Earth, some in space-to glean information about distant objects from the electromagnetic radiation they give off.

Radio waves

Giant satellite-dish antennas pick up long-wavelength, high-frequency radio waves. The biggest radio telescope on Earth is the Five-hundred-meter Aperture Spherical Telescope (FAST) in China, which is getting on for twice the size of the much better known 305m (1000ft) Arecibo Observatory in Puerto Rico. The dish pictured here is about seven times smaller than FAST and four times smaller than Arecibo. It's the 70m (230ft) Canberra deep dish satellite in Australia.

Microwaves

Because cosmic microwaves can't get through the whole of Earth's atmosphere, we have to study them from space. Cosmic Background Explorer (COBE), launched in 1989 and deactivated in 1993, was a space satellite designed to do this. These images of the night sky were taken by COBE using different wavelengths of infrared light.

Infrared

Water in Earth's atmosphere absorbs infrared; studying that kind of electromagnetic radiation is another job for a space-based satellite, such as the Infrared Astronomical Satellite (IRAS), which operated for 10 months during 1983. This is an image of the Andromeda Galaxy taken by IRAS.

Visible light

Visible light shooting in from space is one thing we can easily study from Earth with any conventional, optical telescope. This one is the historic 66cm (26inch) refractor telescope at the U.S. Naval Observatory in Washington, D.C. However, Earth-bound telescopes like this can pick up only so much-hence the need for telescopes (like the Hubble and its replacement, the James Webb) that travel into space.

Ultraviolet light

Ultraviolet light can cause skin cancer, so it's a good job much of it is absorbed by Earth's ozone layer. Unfortunately, the downside of this is that we have to study ultraviolet light coming from space using satellites such as the International Ultraviolet Explorer (IUE), which operated for almost two decades between 1978 and 1996.

X rays

Think of X rays and you probably think of broken bones-but they're whizzing round space too. Earth's atmosphere prevents these dangerous, high-energy rays from reaching telescopes on the ground, but space telescopes, such as the Roentgen Satellite (ROSAT) (which operated between 1990 and 1999), have been able to observe them in space. The Sun looks the way it does because our eyes see only a fraction of the electromagnetic radiation it gives off. If we could see X rays, the Sun might look more like it does in this image taken taken in December 2001 by the Soft X ray Telescope (SXT), an instrument onboard the Yohkoh observatory spacecraft. What does the Sun really look like? We can never know: our eyes can't appreciate it completely!

Photo by courtesy of NASA Goddard Space Flight Center (NASA-GSFC).

Gamma rays

High-energy gamma rays are also blocked by Earth's atmosphere, so we need space-based telescopes to study those too, such as the Compton Gamma-Ray Observatory, which operated from 1991 to 2000. This photo shows the Compton whizzing over Baja California, Mexico in 1991, and was taken from the Space Shuttle that launched it). The Compton was named for US physicist Arthur Holly Compton (1892-1962), one of the first scientists to study cosmic rays.

Find out more

On this website

On other sites

Books for younger readers

NASA: Tour of the Electromagnetic Spectrum by Ginger Butcher. NASA, 2016. A free, colorful 32-page introduction written at a similar level to my own article, but with more detail. You can download it as a PDF by clicking on "Go to resource."

Science Pathways: Electricity by Chris Woodford. Rosen, 2013. One of my books covering the story of electricity, from the ancient Greeks, through James Clerk Maxwell, up to modern-day electronics and computing (suitable for ages 9-12).

Eyewitness: Electricity by Steve Parker. DK, 2005. What is electricity and how does it power our world?

Articles

More to explore on our website...

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Electromagnetic spectrum - Types of electromagnetic waves compared

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by Chris Woodford. Last updated: May 7, 2018. You might think the world is essentially what you can see in front of you, but think for a moment and you'll realize this isn't true. When you close your eyes, the world doesn't cease to exist just because there's no light to see by.