Light Basics Types of Light Light Gallery The EM Spectrum

DID YOU find all seven types of light in the PUZZLE? 
If YOU DID, CONGRATULATIONS!  By now you know that different types of light have different wavelengths.  But what does this mean in nature?  What objects emit what types of light? READ ON...

While the atmosphere protects us from harmful radiation, it also limits the amount of information reaching astronomers on the ground. As you go through the information below, see if you can figure out which light types have trouble getting through the Earth's atmosphere.

Radio Waves

  • How Large are Radio Waves? Of all types of light, radio waves have the longest wavelengths. Radio waves are longer than 1 mm and can be very long.
  • In fact, the most common radio emission in the galaxy is at 21 cm, (about the length of the average forearm). This radiation is produced by hydrogen atoms.
  • Astronomers use the 21 cm radio radiation to probe the gas and dust located between stars.
  • Good Sources of Radio Waves: Hydrogen atoms, like we mentioned, are good sources of radio waves. Other sources of radio emission are from stars like our Sun. Distant galaxies or quasars (luminous objects at the center of some galaxies) can also be bright radio sources.
  • Radio telescopes have to be large in order to capture these long waves. Scientists and engineers sometimes build several antenna dishes that they hook up together to capture or record radio waves with more detail than single dishes can provide. These are called "arrays."
  • The Very Large Array located in Socorro, New Mexico is one of the world's premiere astronomical radio observatories. The VLA consists of 27 antennas arranged in a huge Y pattern up to 36km (22 miles) across -- roughly one and a half times the size of Washington, D.C.


  • Sources of Microwaves: The universe is glowing in microwaves
  • These microwaves are thought to be the leftover radiation from the big bang at the beginning of the universe.
  • The universal microwave glow was discovered by accident--as a source of "noise" in a backyard telescope!
  • In 1998, the COsmic Background Explorer satellite, COBE, gave us the first map of the intensity of the microwave background in every direction. Today, NASA is preparing to launch MAP, the Microwave Anisotropy Probe, to make  detailed studies of the microwave background.


  • What Causes Infrared? A lot of the infrared radiation we detect in the Universe is caused by dust. Dust particles are heated by higher energy radiation (like visible and ultraviolet light) and then re-emit the heat as infrared light.
  • Good Places to Find Infrared Sources: Infrared images show the distribution of heat. All warm objects give off infrared. Infrared light emission is found in regions of space where large amounts of gas and dust are condensing to form new stars, so called "stellar nurseries."
  • Infrared is absorbed almost completely in the lower layers of the Earth's atmosphere. For this reason, infrared astronomy has to be conducted from the highest mountain tops, airplanes, or satellites.
  • Unlike visible light, infrared shows through dust clouds in our Galaxy. So objects like the center of our galaxy, which we can't see in visible light because dust clouds are in the way, can be "seen" by looking at the infrared light given off.


  • What Your Eyes See: Our Sun produces a lot of visible light, so that is what human eyes evolved to see. Sometimes scientists call this the optical range of light. This has been the most studied wavelength range. Astronomers will often work in the shorter wavelength "blue end" if they are interested in slightly hotter stars or the longer wavelength "red end" for cooler ones.
  • What are Good Sources of Visible Light? When a star ages, its outer envelope can expand to 50 times its normal size. When it expands, it cools and looks red. It is then called a "red-giant" star. You can see that stars have different colors by looking at the constellation Orion this Fall. The star to the north is the red-giant Betelgeuse, compare how it looks to the star in the lower right corner of Orion, which is Rigel a hotter younger star. Other objects frequently observed in visible light are the Moon, solar system objects (Mars, Venus, our Sun, etc.), stars, and other galaxies.
  • Of course, we see all sorts of things on Earth. The Sun's light we see reflected off of objects on Earth is visible light. Because visible light reaches us, we can observe objects like the Sun, the Moon, planets, and stars from ground-based telescopes. Some famous visible light telescopes are, Keck Telescope in Hawaii, Kitt Peak National Observatory in Arizona, and Cerro Tololo Inter-American Observatory in Chile
  • Here's Some Easy-To-Do Visible Light Activities at the Exploratorium. (Will appear in your second window)
  • Keck Observatory domesKeck Observatory atop Mauna Kea on the Big Island of Hawaii. The Keck Telescope is eight stories tall and weighs 300 tons.

Ultraviolet (UV)

  • Good Sources of UV: Ultraviolet radiation comes from hotter objects, including bright young stars, white dwarfs, and binary stars, which are two stars orbiting around one another. Ultraviolet astronomy has been used to show that practically all stars, including even some white dwarfs (stars at the end of their lives), lose matter in the form of stellar winds.
  • Ultraviolet light has a difficult time getting through the Earth's atmosphere, so much of ultraviolet astronomy is done from satellites.

Extreme Ultraviolet (EUV)

  • Good Sources of EUV: EUV tends to come from objects that are really hot. For instance, white dwarf stars, which are typically ten of thousands of degrees. White dwarfs are stars near the end of their lives. Once the nuclear energy production has stopped, gravity can squeeze a star the size of our Sun down to the size of the Earth. The "burnt-out" Earth-sized star then cools for millions of years like a brick out of an oven.
  • The outer envelopes of stars, typically hundreds of thousands of degrees, produce EUV light. The Sun, whose outer corona is about 1 million degrees, emits a lot of EUV radiation.  This makes it hard to do EUV astronomy without some sort of "sun shade." 
  • Like most ultraviolet light, extreme ultraviolet light does not go through the Earth's atmosphere, so much of extreme ultraviolet astronomy is done from satellites. The  Extreme Ultraviolet Explorer,  pictured below, was one such satellite.

  • Artist's conception of the EUVE satellite in orbit.Extreme Ultraviolet Explorer Satellite




  • What Causes X-Rays? X-rays are produced by very energetic events such as the falling of material ("accretion") onto the surface of a compact object like a white dwarf star or neutron star. 
  •  A neutron star is a dead star in which gravity has squeezed all of the matter into the size of a small city. One tablespoon of a neutron star would weigh as much as the entire human race. A black-hole is the extreme case of a compact object, where gravity is so strong not even light can escape from its surface. 
  • When a neutron star and an ordinary star are rotating around one another in a binary system, the neutron star's tremendous gravity attracts material from the normal star.  As the material "falls" toward the neutron star, it is heated to millions of degrees and emits X-rays. This is similar to a rock  falling from a great height and releasing its energy as shock and noise on impact with the ground, but much more energetic!  
  • Matter falling into a black hole will undergo the same heating as it spirals inward, generating many x-rays.  Since the black hole emits no radiation of its own (no light can escape), the only way scientists can determine the locations of black holes is by looking for the x-rays from the surrounding matter. 
  • X-rays also come from acceleration of particles in outer parts of a star's atmosphere or corona. Our Sun is a bright source of X-rays. X-rays are also produced in distant galaxies or Quasars where it thought that a very massive black hole (billion times more massive than our Sun) is accreting matter in the center.
  • No X-rays from space can get through the Earth's atmosphere to the ground, so all X-ray astronomy is carried out with instruments on rockets or satellites.

Gamma Rays

  • Where Do Gamma Rays Come From? Gamma Rays are caused by some of the most energetic events in the Universe. Gamma rays are often produced in regions of extremely high temperature. Gamma rays come from solar flares, or eruptions on the sun's surface,  pulsars (rotating magnetic objects which emit jets of radiation), The nova and super nova explosions that cause stars to become extremely bright before they collapse also produce gamma rays.  Material falling onto black holes,  known as accretion, causes gamma rays as well as x-rays.

  • The Compton Gamma Ray Observatory was launched by the Space Shuttle Atlantis of 1991 into a near Earth circular orbit.


Did you notice that scientists use orbiting spacecraft and satellites to go above the atmosphere to collect data from the shorter light wavelengths such as gamma rays, X-Rays, ultraviolet and extreme ultraviolet? Take a look at this image to see how the atmosphere protects us from harmful radiation but limits the amount of information reaching astronomers.


Now go on to your final challenge- picture the entire electromagnetic spectrum.

Light Basics Types of Light Light Gallery The EM Spectrum

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