Why is it useful to observe a celestial object in more than one part of the electromagnetic spectrum

The universe is full of amazing things, but we need help to see most of them. There are many types of light that our eyes cannot see, so we use instruments, such as telescopes, that can detect this hidden light.

About light

Most objects in space give off (radiate) light. This light is given different names, depending on its wavelength and energy – radio waves (long wavelength, low energy), microwaves, infrared, visible light, ultraviolet, X-rays and gamma rays (short wavelength, high energy). Scientists call the whole range of light types the electromagnetic spectrum. They don’t use the word ‘light’ because most of us think of light as just what we can see with our eyes. Get used to using the scientific term electromagnetic spectrum when talking about light.

Our eyes only see a very small part of the electromagnetic spectrum, so we need special instruments to detect the rest. Even though you may not be able to see certain wavelengths, you will have experienced them in one way or the other:

• Radio waves – you can’t see them, but you’ve listened to the radio.
• Microwaves – you may have used them to heat your food.
• UV – can give you sunburn.
• X-rays – reveal broken bones.

Even though you can’t see them with your eyes, they are there, and we use different instruments to make them visible.

Most objects in space give off several types of electromagnetic radiation at the same time. What they radiate depends on many things, such as how hot they are and what they are made of. Astronomers collect information about the radiation from space objects to find out about such things as the births and deaths of stars, how hot objects are, how far away they are, even how the universe was formed.

Telescopes and the electromagnetic spectrum

Astronomers use telescopes that detect different parts of the electromagnetic spectrum. Each type of telescope can only detect one part of the electromagnetic spectrum. There are radio telescopes, infrared telescopes, optical (visible light) telescopes and so on.

We can’t see most of the radiation detected, so computers turn data into images we can see. Many of the images you see of space have amazing colours – these are called false colours because computers have taken the data from wavelengths we can’t see and presented them as colours we can see.

Astronomers have a huge problem detecting radiation from space because the Earth’s atmosphere blocks most of it and stops it from reaching the surface. Visible light and radio waves get through to telescopes on the ground, and some detectors (infrared, UV and gamma) work when they are high up on mountains. The best place to detect most radiation is above the blocking atmosphere, so some telescopes are put in orbit around the Earth. Even visible light is distorted by the atmosphere, so clearer pictures can be got from orbiting telescopes. For example, the Hubble Space Telescope is positioned outside the Earth’s atmosphere and takes very sharp images of very distant objects in space.

The activity Exploring with telescopes uses an interactive and an online or paper-based quiz to learn about different types of telescopes and the types of space objects they are best suited to view.

In the activity, Shrink the Solar System, students create a scale model of the Solar System to help them understand distances in space.

Light carries information in ways you may not realize. Cell phones use light to send and receive calls and messages. Wireless routers use light to send pictures of cats from the internet to your computer. Car radios use light to receive music from nearby radio stations. Even in nature, light carries many kinds of information.  

Telescopes are light collectors, and everything we know from Hubble is because of light. Since we are not able to travel to a star or take samples from a faraway galaxy, we must depend on electromagnetic radiation — light — to carry information to us from distant objects in space.

The Hubble Space Telescope can view objects in more than just visible light, including ultraviolet, visible and infrared light. These observations enable astronomers to determine certain physical characteristics of objects, such as their temperature, composition and velocity.

What Is the Electromagnetic Spectrum?

The electromagnetic spectrum describes all of the kinds of light, including those the human eye cannot see. In fact, most of the light in the universe is invisible to our eyes.

The light we can see, made up of the individual colors of the rainbow, represents only a very small portion of the electromagnetic spectrum. Other types of light include radio waves, microwaves, infrared radiation, ultraviolet rays, X-rays and gamma rays — all of which are imperceptible to human eyes.

All light, or electromagnetic radiation, travels through space at 186,000 miles (300,000 kilometers) per second — the speed of light. That’s about as far as a car will go over its lifetime, traveled by light in a single second! 

How We Measure Light

Your eyes detect electromagnetic waves that are roughly the size of a virus. Your brain interprets the various energies of visible light as different colors, ranging from red to violet. Red has the lowest energy and violet the highest.  

Beyond red and violet are many other kinds of light our human eyes can’t see, much like there are sounds our ears can’t hear. On one end of the electromagnetic spectrum are radio waves, which have wavelengths billions of times longer than those of visible light. On the other end of the spectrum are gamma rays, with wavelengths billions of times smaller than those of visible light.

Scientists use color as a tool to convey information. Read the article

Scientists use different techniques with telescopes to isolate different types of light. For example, although our eyes cannot see ultraviolet light from a star, one way to perceive it is to let the star’s light pass through a filter on a telescope that removes all other kinds of light and fall on a special telescope camera sensitive to ultraviolet light.

What Different Types of Light Tell Us

To study the universe, astronomers employ the entire electromagnetic spectrum. Different types of light tell us different things.  See interactive examples

Radio waves and microwaves, which have the lowest energies, allow scientists to pierce dense, interstellar clouds to see the motion of cold gas.

Infrared light is used to see through cold dust; study warm gas and dust, and relatively cool stars; and detect molecules in the atmospheres of planets and stars.

Most stars emit the bulk of their electromagnetic energy as visible light, that sliver of the spectrum our eyes can see. Hotter stars emit higher energy light, so the color of the star indicates how hot it is. This means that red stars are cool, while blue stars are hot. 

Beyond violet lies ultraviolet (UV) light, whose energies are too high for human eyes to see. UV light traces the hot glow of stellar nurseries and is used to identify the hottest, most energetic stars.

X-rays come from the hottest gas that contains atoms. They are emitted from superheated material spiraling around a black hole, seething neutron stars, or clouds of gas heated to millions of degrees.

Gamma rays have the highest energies and shortest wavelengths on the electromagnetic spectrum. They come from free electrons and stripped atomic nuclei accelerated by powerful magnetic fields in exploding stars, colliding neutron stars, and supermassive black holes.

Last Updated:
May 30, 2019