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The Electromagnetic Spectrum

Visual light seen by the human eye is only one type of energy found in the universe and represents the smallest part of the electromagnetic spectrum.

Units of electromagnetic radiation are particles known as photons that travel along wavelengths at varying frequencies, providing heat and both visible and invisible light. A wave is characterized by two things: frequency, the number of waves that occur during an interval of time, and wavelength, the length of a single wave. Frequency and wavelength are inversely proportional – the faster the frequency the shorter the wavelength.

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  • Radio waves have the longest wavelength. Stars, planets, and galaxies, as well as Sagittarius A* at the center of the Milky Way galaxy, all emit radio waves. Here on earth, this part of the electromagnetic spectrum has practical uses in communication and broadcasting. Waves with either modulated amplitudes (AM) or modulated frequencies (FM) are generated by telecommunication stations. These waves of sound energy are captured with a radio antenna and then “tuned” into on a specific frequency.
  • Microwaves range in size from a meter to a millimeter. This smaller wavelength is used in satellite, computer, and radar communication systems, including GPS navigation around the world and into space. On a practical basis, microwaves are a safe and effective way to cook food since they’re a non-ionizing form of radiation.
  • Infrared light was discovered as heat energy in the year 1800 when astronomer William Herschel observed that an invisible part of a refracted light source reacted with a thermometer. Thermal heat is everywhere in the environment and can be detected with infrared sensors such as night vision goggles. In the subzero vacuum of outer space, astronomers can identify objects within dense molecular clouds as they absorb thermal energy from nearby stars.
  • Visible light is the only part of the electromagnetic spectrum that can be seen by the human eye. When white light is refracted through a prism, it diffuses into a rainbow of bright colors, each with a different wavelength. Everything in the environment interacts with light and either emits, absorbs, or reflects it. Most of the light around us is from thermal sources like the sun, electric light bulbs, or candle flames.
  • Ultraviolet light is emitted from the sun and absorbed in the outer layers of the earth’s atmosphere. This type of energy is radiated at a higher frequency and is considered a dangerous type of ionizing radiation. On earth, UV light has practical uses and health benefits that have to be cautiously balanced against potential dangers. For instance, sunlight is necessary for good health as it activates the chemical reaction that generates Vitamin D. Too much exposure, however, could cause sunburns, premature aging, and skin cancer.
  • X-rays have revolutionalized the field of medicine. Photons of radiation traveling at this speed pass through soft tissue while being absorbed by denser objects such as bone, allowing doctors to cautiously and non-invasively diagnose and treat many types of injuries. X-rays were discovered in the 19th century and resulted in painful side effects and fatal injuries until scientists better understood this type of radiation. Targeted exposure to high levels of x-rays results in damage to cell structures and to DNA. Today, these properties are used in a beneficial way to kill cancer cells and shrink tumors.
  • Gamma rays are a deadly form of ionizing radiation. They’re emitted by the sun during dangerous solar flares, detected in lightning storms, and they’re found in massive high energy explosions such as supernovas. A photon of light at such a high frequency has enough energy to change the molecular structure of objects in its way, including live tissue, which begins to decompose as a result of cellular damage.