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A comparison for the size of the wave

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A comparison for the size of the wave

Frequency range

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A comparison for the size of the wave

Frequency range

Use for radiation?

Harmful to life?

Visual Examples

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A comparison for the size of the wave

Frequency range

Use for radiation?

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Visual examples

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A comparison for the size of the wave

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The basic building block of radio communications is a radio wave. Like waves on a pond, a radio wave is a series of repeating peaks and valleys.

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A radio tuner receives radio waves and converts them to mechanical vibrations in the speaker to create sound waves that can be heard.

Credit: Ensuper | Shutterstock

Radio waves are a type of electromagnetic radiation best-known for their use in communication technologies, such as television, mobile phones and radios. These devices receive radio waves and convert them to mechanical vibrations in the speaker to create sound waves.

The radio-frequency spectrum is a relatively small part of the electromagnetic (EM) spectrum. The EM spectrum is generally divided into seven regions in order of decreasing wavelength and increasing energy and frequency, according to the University of Rochester. The common designations are radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays.

Radio waves have the longest wavelengths in the EM spectrum, according to NASA, ranging from about 0.04 inches (1 millimeter) to more than 62 miles (100 kilometers). They also have the lowest frequencies, from about 3,000 cycles per second, or 3 kilohertz, up to about 300 billion hertz, or 300 gigahertz.

The radio spectrum is a limited resource and is often compared to farmland. Just as farmers must organize their land to achieve the best harvest regarding quantity and variety, the radio spectrum must be split among users in the most efficient way, according to the British Broadcasting Corp. (BBC). In the U.S., the National Telecommunications and Information Administration within the United States Department of Commerce manages the frequency allocations along the radio spectrum.

Scottish physicist James Clerk Maxwell, who developed a unified theory of electromagnetism in the 1870s, predicted the existence of radio waves, according to the National Library of Scotland. In 1886, Heinrich Hertz, a German physicist, applied Maxwell's theories to the production and reception of radio waves. Hertz used simple homemade tools, including an induction coil and a Leyden jar (an early type of capacitor consisting of a glass jar with foil layers both inside and out) to create electromagnetic waves. Hertz became the first person to transmit and receive controlled radio waves. The unit of frequency of an EM wave - one cycle per second - is called a hertz, in his honor, according to the American Association for the Advancement of Science.

The National Telecommunications and Information Administration generally divides the radio spectrum into nine bands:

ELF radio waves, the lowest of all radio frequencies, have a long range and are useful in penetrating water and rock for communication with submarines and inside mines and caves. The most powerful natural source of ELF/VLF waves is lightning, according to the Stanford VLF Group. Waves produced by lightning strikes can bounce back and forth between Earth and the ionosphere (the atmosphere layer with a high concentration of ions and free electrons), according to Phys.org. These lightning disturbances can distort important radio signals traveling to satellites.

LF and MF radio bands include marine and aviation radio, as well as commercial AM (amplitude modulation) radio, according to RF Page. AM radio frequency bands fall between 535 kilohertz to 1.7 megahertz, according to How Stuff Works. AM radio has a long range, particularly at night when the ionosphere is better at refracting the waves back to earth, but it is subject to interference that affects the sound quality. When a signal is partially blocked - for example, by a metal-walled building such as a skyscraper - the volume of the sound is reduced accordingly.

HF, VHF and UHF bands include FM radio, broadcast television sound, public service radio, cellphones and GPS (global positioning system). These bands typically use "frequency modulation" (FM) to encode, or impress, an audio or data signal onto the carrier wave. In frequency modulation, the amplitude (maximum extent) of the signal remains constant while the frequency is varied higher or lower at a rate and magnitude corresponding to the audio or data signal.

FM results in better signal quality than AM because environmental factors do not affect the frequency the way they affect amplitude, and the receiver ignores variations in amplitude as long as the signal remains above a minimum threshold. FM radio frequencies fall between 88 megahertz and 108 megahertz, according to How Stuff Works.

Shortwave radio uses frequencies in the HF band, from about 1.7 megahertz to 30 megahertz, according to the National Association of Shortwave Broadcasters (NASB). Within that range, the shortwave spectrum is divided into several segments, some of which are dedicated to regular broadcasting stations, such as the Voice of America, the British Broadcasting Corp. and the Voice of Russia. Throughout the world, there are hundreds of shortwave stations, according to the NASB. Shortwave stations can be heard for thousands of miles because the signals bounce off the ionosphere, and rebound back hundreds or thousands of miles from their point of origin.

SHF and EHF represent the highest frequencies in the radio band and are sometimes considered to be part of the microwave band. Molecules in the air tend to absorb these frequencies, which limits their range and applications. However, their short wavelengths allow signals to be directed in narrow beams by parabolic dish antennas (satellite dish antennas). This allows for short-range high-bandwidth communications to occur between fixed locations.

SHF, which is affected less by the air than EHF, is used for short-range applications such as Wi-Fi, Bluetooth and wireless USB (universal serial bus). SHF can work only in line-of-sight paths as the waves tend to bounce off objects like cars, boats and aircraft, according to the RF Page. And because the waves bounce off objects, SHF can also be used for radar.

Outer space is teeming with sources of radio waves: planets, stars, gas and dust clouds, galaxies, pulsars and even black holes. By studying these, astronomers can learn about the motion and chemical composition of these cosmic sources as well as the processes that cause these emissions.

A radio telescope "sees" the sky very differently than it appears in visible light. Instead of seeing point-like stars, a radio telescope picks up distant pulsars, star-forming regions and supernova remnants. Radio telescopes can also detect quasars, which is short for quasi-stellar radio source. A quasar is an incredibly bright galactic core powered by a supermassive black hole. Quasars radiate energy broadly across the EM spectrum, but the name comes from the fact that the first quasars to be identified emit mostly radio energy. Quasars are highly energetic; some emit 1,000 times as much energy as the entire Milky Way.

Radio astronomers often combine several smaller telescopes, or receiving dishes, into an array in order to make a clearer, or higher-resolution, radio image, according to the University of Vienna. For example, the Very Large Array (VLA) radio telescope in New Mexico consists of 27 antennas arranged in a huge "Y" pattern that's 22 miles (36 kilometers) across.

Additional resources:

This article was updated on Feb. 27, 2019 by Live Science contributor Traci Pedersen.

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Radio waves are a type of electromagnetic radiation best-known for their use in communication technologies, such as television, mobile phones and radios. These devices receive radio waves and convert them to mechanical vibrations in the speaker to create sound waves. The radio-frequency spectrum is a relatively small part of the electromagnetic (EM) spectrum.

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(Image credit: ESA and the Planck Collaboration)

Microwaves are a type of electromagnetic radiation, as are radio waves, ultraviolet radiation, X-rays and gamma-rays. Microwaves have a range of applications, including communications, radar and, perhaps best known by most people, cooking.

Electromagnetic radiation is transmitted in waves or particles at different wavelengths and frequencies. This broad range of wavelengths is known as the electromagnetic spectrum EM spectrum). The spectrum is generally divided into seven regions in order of decreasing wavelength and increasing energy and frequency. The common designations are radio waves, microwaves, infrared (IR), visible light, ultraviolet (UV), X-rays and gamma-rays. Microwaves fall in the range of the EM spectrum between radio and infrared light.

(Image credit: Shutterstock)

Microwaves have frequencies ranging from about 1 billion cycles per second, or 1 gigahertz (GHz), up to about 300 gigahertz and wavelengths of about 30 centimeters (12 inches) to 1 millimeter (0.04 inches), according to the Encyclopedia Britannica. This region is further divided into a number of bands, with designations such as L, S, C, X and K, according to Ginger Butcher's book "Tour of the Electromagnetic Spectrum."

Communications & radar

Microwaves are used mostly for point-to-point communications systems to convey all types of information, including voice, data and video in both analog and digital formats, according to the Federal Communications Commission (FCC). They are also used for supervisory control and data acquisition (SCADA) for remote machinery, switches, valves and signals.

Another important application of microwaves is radar. The word "radar" was originally an acronym for RAdio Detection And Ranging. Prior to World War II, British radio engineers found that short-wavelength radio waves could be bounced off distant objects like ships and aircraft, and the returning signal could be detected with highly sensitive directional antennas so the presence and locations of those objects could be determined. Usage of the term "radar" has become so common that it is now a word in and of itself, and can refer to systems that use microwaves or radio waves.

A little-known historical fact is that an early radar installation was built atop Kahuku Point on Oahu's northernmost tip. According to the state of Hawaii's website, the station actually detected the first wave of Japanese aircraft on their way to attack Pearl Harbor when the planes were 132 miles (212 kilometers) out. However, because the system had been in operation for only two weeks, it was considered unreliable, and the warning was ignored. Over the course of the war, radar was improved and refined, and it has since become an essential element of national defense and civilian air-traffic control.

Radar has found many other uses, some of which exploit the Doppler effect. An example of the Doppler effect can be demonstrated by an approaching ambulance: As it nears, the sound of the siren seems to rise in pitch, until it wails by. Then, as it recedes into the distance, the siren seems to lower in pitch.

Robert Mayanovic, a professor of physics at Missouri State University, said that Doppler radar, which often employs microwaves, is used for air-traffic control and vehicular speed-limit enforcement. When an object is approaching the antenna, the returning microwaves are compressed and thus have a shorter wavelength and higher frequency. Conversely, return waves from objects moving away are elongated and have a longer wavelength and lower frequency. By measuring this frequency shift, the speed of an object toward or away from the antenna can be determined.

Common applications of this principle include simple motion detectors, radar guns for speed-limit enforcement, radar altimeters and weather radar that can track the 3D motion of water droplets in the atmosphere. These applications are called active sensing, because microwaves are transmitted, and the reflected signals are received and analyzed. In passive sensing, natural sources of microwaves are observed and analyzed. Many of these observations are conducted

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Microwaves are a type of electromagnetic radiation, and are useful in communications, radar and cooking.

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MICROWAVES

You may be familiar with microwave images as they are used on TV weather news and you can even use microwaves to cook your food. Microwave ovens work by using microwave about 12 centimeters in length to force water and fat molecules in food to rotate. The interaction of these molecules undergoing forced rotation creates heat, and the food is cooked.

MICROWAVE BANDS

Microwaves are a portion or "band" found at the higher frequency end of the radio spectrum, but they are commonly distinguished from radio waves because of the technologies used to access them. Different wavelengths of microwaves (grouped into "sub-bands") provide different information to scientists. Medium-length (C-band) microwaves penetrate through clouds, dust, smoke, snow, and rain to reveal the Earth's surface. L-band microwaves, like those used by a Global Positioning System (GPS) receiver in your car, can also penetrate the canopy cover of forests to measure the soil moisture of rain forests. Most communication satellites use C-, X-, and Ku-bands to send signals to a ground station.

Microwaves that penetrate haze, light rain and snow, clouds, and smoke are beneficial for satellite communication and studying the Earth from space. The SeaWinds instrument onboard the Quick Scatterometer (QuikSCAT) satellite uses radar pulses in the Ku-band of the microwave spectrum. This scatterometer measures changes in the energy of the microwave pulses and can determine speed and direction of wind near the ocean surface. The ability of microwaves to pass through clouds enables scientists to monitor conditions underneath a hurricane.

ACTIVE REMOTE SENSING

Radar technology is considered an active remote sensing system because it actively sends a microwave pulse and senses the energy reflected back. Doppler Radar, Scatterometers, and Radar Altimeters are examples of active remote sensing instruments that use microwave frequencies.

The radar altimeter onboard the joint NASA/CNES (French space agency) Ocean Surface Topography Mission (OSTM)/Jason-2 satellite can determine the height of the sea surface. This radar altimeter beams microwaves at two different frequencies (13.6 and 5.3 GHz) at the sea surface and measures the time it takes the pulses to return to the spacecraft. Combining data from other instruments that calculate the spacecraft's precise altitude and correct for the effect of water vapor on the pulse can determine the sea surface height within just a few centimeters!

PASSIVE REMOTE SENSING

Passive remote sensing refers to the sensing of electromagnetic waves that did not originate from the satellite or instrument itself. The sensor is merely a passive observer collecting electromagnetic radiation. Passive remote sensing instruments onboard satellites have revolutionized weather forecasting by providing a global view of weather patterns and surface temperatures. A microwave imager onboard NASA's Tropical Rainfall Measuring Mission (TRMM) can capture data from underneath storm clouds to reveal the underlying rain structure.

CLUES TO THE BIG BANG

In 1965, using long, L-band microwaves, Arno Penzias and Robert Wilson, scientists at Bell Labs, made an incredible discovery quite by accident: they detected background noise using a special low-noise antenna. The strange thing about the noise was that it was coming from every direction and did not seem to vary in intensity much at all. If this static were from something on our planet, such as radio transmissions from a nearby airport control tower, it would come only from one direction, not everywhere. The Bell Lab scientists soon realized that they had serendipitously discovered the cosmic microwave background radiation. This radiation, which fills the entire universe, is a clue to its beginning, known as the Big Bang.

The image below from the Wilkinson Microwave Anisotropy Probe (WMAP) shows a detailed, all-sky picture of the infant universe at 380,000 years of age. This light, emitted 13.7 billon-years ago, is ∼2.7 Kelvin today. The observed +/-200 microKelvin temperature fluctuations, shown as color differences in the image, are the seeds that grew to become clusters of galaxies.

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Citation

APA

National Aeronautics and Space Administration, Science Mission Directorate. (2010). Microwaves. Retrieved [insert date - e.g. August 10, 2016], from NASA Science website: http://science.nasa.gov/ems/06_microwaves

MLA

Science Mission Directorate. "Microwaves" NASA Science. 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov/ems/06_microwaves

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This Doppler-radar image seen on TV weather news uses microwaves for local weather forecasting. Shown here is Hurricane Claudette's eye-wall making landfall. Credit: NOAA MICROWAVES You may be familiar with microwave images as they are used on TV weather news and you can even use microwaves to cook your food.

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What are Infrared Waves?

Infrared waves, or infrared light, are part of the electromagnetic spectrum. People encounter Infrared waves every day; the human eye cannot see it, but humans can detect it as heat.

A remote control uses light waves just beyond the visible spectrum of light-infrared light waves-to change channels on your TV. This region of the spectrum is divided into near-, mid-, and far-infrared. The region from 8 to 15 microns (µm) is referred to by Earth scientists as thermal infrared since these wavelengths are best for studying the longwave thermal energy radiating from our planet.

DISCOVERY OF INFRARED

In 1800, William Herschel conducted an experiment measuring the difference in temperature between the colors in the visible spectrum. He placed thermometers within each color of the visible spectrum. The results showed an increase in temperature from blue to red. When he noticed an even warmer temperature measurement just beyond the red end of the visible spectrum, Herschel had discovered infrared light!

THERMAL IMAGING

We can sense some infrared energy as heat. Some objects are so hot they also emit visible light-such as a fire does. Other objects, such as humans, are not as hot and only emit only infrared waves. Our eyes cannot see these infrared waves but instruments that can sense infrared energy-such as night-vision goggles or infrared cameras-allow us to "see" the infrared waves emitting from warm objects such as humans and animals. The temperatures for the images below are in degrees Fahrenheit.

COOL ASTRONOMY

Many objects in the universe are too cool and faint to be detected in visible light but can be detected in the infrared. Scientists are beginning to unlock the mysteries of cooler objects across the universe such as planets, cool stars, nebulae, and many more, by studying the infrared waves they emit.

The Cassini spacecraft captured this image of Saturn's aurora using infrared waves. The aurora is shown in blue, and the underlying clouds are shown in red. These aurorae are unique because they can cover the entire pole, whereas aurorae around Earth and Jupiter are typically confined by magnetic fields to rings surrounding the magnetic poles. The large and variable nature of these aurorae indicates that charged particles streaming in from the Sun are experiencing some type of magnetism above Saturn that was previously unexpected.

SEEING THROUGH DUST

Infrared waves have longer wavelengths than visible light and can pass through dense regions of gas and dust in space with less scattering and absorption. Thus, infrared energy can also reveal objects in the universe that cannot be seen in visible light using optical telescopes. The James Webb Space Telescope (JWST) has three infrared instruments to help study the origins of the universe and the formation of galaxies, stars, and planets.

A pillar composed of gas and dust in the Carina Nebula is illuminated by the glow from nearby massive stars shown below in the visible light image from the Hubble Space Telescope. Intense radiation and fast streams of charged particles from these stars are causing new stars to form within the pillar. Most of the new stars cannot be seen in the visible-light image (left) because dense gas clouds block their light. However, when the pillar is viewed using the infrared portion of the spectrum (right), it practically disappears, revealing the baby stars behind the column of gas and dust.

MONITORING THE EARTH

To astrophysicists studying the universe, infrared sources such as planets are relatively cool compared to the energy emitted from hot stars and other celestial objects. Earth scientists study infrared as the thermal emission (or heat) from our planet. As incident solar radiation hits Earth, some of this energy is absorbed by the atmosphere and the surface, thereby warming the planet. This heat is emitted from Earth in the form of infrared radiation. Instruments onboard Earth observing satellites can sense this emitted infrared radiation and use the resulting measurements to study changes in land and sea surface temperatures.

There are other sources of heat on the Earth's surface, such as lava flows and forest fires. The Moderate Resolution Imaging Spectroradiometer (MODIS) instrument onboard the Aqua and Terra satellites uses infrared data to monitor smoke and pinpoint sources of forest fires. This information can be essential to firefighting efforts when fire reconnaissance planes are unable to fly through the thick smoke. Infrared data can also enable scientists to distinguish flaming fires from still-smoldering burn scars.

The global image on the right is an infrared image of the Earth taken by the GOES 6 satellite in 1986. A scientist used temperatures to determine which parts of the image were from clouds and which were land and sea. Based on these temperature differences, he colored each separately using 256 colors, giving the image a realistic appearance.

Why use the infrared to image the Earth? While it is easier to distinguish clouds from land in the visible range, there is more detail in the clouds in the infrared. This is great for studying cloud structure. For instance, note that darker clouds are warmer, while lighter clouds are cooler. Southeast of the Galapagos, just west of the coast of South America, there is a place where you can distinctly see multiple layers of clouds, with the warmer clouds at lower altitudes, closer to the ocean that's warming them.

We know, from looking at an infrared image of a cat, that many things emit infrared light. But many things also reflect infrared light, particularly near infrared light. Learn more about REFLECTED Near-infrared radiation.

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Citation

APA

National Aeronautics and Space Administration, Science Mission Directorate. (2010). Infrared Waves. Retrieved [insert date - e.g. August 10, 2016], from NASA Science website: http://science.nasa.gov/ems/07_infraredwaves

MLA

Science Mission Directorate. "Infrared Waves" NASA Science. 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov /ems/07_infraredwaves

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What are Infrared Waves? Infrared waves, or infrared light, are part of the electromagnetic spectrum. People encounter Infrared waves every day; the human eye cannot see it, but humans can detect it as heat. A remote control uses light waves just beyond the visible spectrum of light-infrared light waves-to change channels on your TV.

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NASA explores the unknown in air and space, innovates for the benefit of humanity, and inspires the world through discovery.

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A comparison for the size of the wave
Frequency Wave
Use for the radiation?
Harmful to life?
Visual examples

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Handout
Book
Links

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What is UV Light?

Ultraviolet (UV) light has shorter wavelengths than visible light. Although UV waves are invisible to the human eye, some insects, such as bumblebees, can see them. This is similar to how a dog can hear the sound of a whistle just outside the hearing range of humans.

ULTRAVIOLET LIGHT FROM OUR SUN

The Sun is a source of the full spectrum of ultraviolet radiation, which is commonly subdivided into UV-A, UV-B, and UV-C. These are the classifications most often used in Earth sciences. UV-C rays are the most harmful and are almost completely absorbed by our atmosphere. UV-B rays are the harmful rays that cause sunburn. Exposure to UV-B rays increases the risk of DNA and other cellular damage in living organisms. Fortunately, about 95 percent UV-B rays are absorbed by ozone in the Earth's atmosphere.

Scientists studying astronomical objects commonly refer to different subdivisions of ultraviolet radiation: near ultraviolet (NUV), middle ultraviolet (MUV), far ultraviolet (FUV), and extreme ultraviolet (EUV). NASA's SDO spacecraft captured the image below in multiple wavelengths of extreme ultraviolet (EUV) radiation. The false-color composite reveals different gas temperatures. Reds are relatively cool (about 60,000 Celsius) while blues and greens are hotter (greater than one million Celsius).

DISCOVERY OF ULTRAVIOLET

In 1801, Johann Ritter conducted an experiment to investigate the existence of energy beyond the violet end of the visible spectrum. Knowing that photographic paper would turn black more rapidly in blue light than in red light, he exposed the paper to light beyond violet. Sure enough, the paper turned black, proving the existence of ultraviolet light.

ULTRAVIOLET ASTRONOMY

Since the Earth's atmosphere absorbs much of the high-energy ultraviolet radiation, scientists use data from satellites positioned above the atmosphere, in orbit around the Earth, to sense UV radiation coming from our Sun and other astronomical objects. Scientists can study the formation of stars in ultraviolet since young stars shine most of their light at these wavelengths. This image from NASA's Galaxy Evolution Explorer (GALEX) spacecraft reveals new young stars in the spiral arms of galaxy M81.

The image to the right shows three different galaxies taken in visible light (bottom three images) and ultraviolet light (top row) taken by NASA's Ultraviolet Imaging Telescope (UIT) on the Astro-2 mission.

The difference in how the galaxies appear is due to which type of stars shine brightest in the optical and ultraviolet wavelengths. Ultraviolet images of galaxies show mainly clouds of gas containing newly formed stars that are many times more massive than the Sun and glow strongly in ultraviolet light. In contrast, visible light images of galaxies show mostly the yellow and red light of older stars. By comparing these types of data, astronomers can learn about the structure and evolution of galaxies.

THE OZONE "HOLE"

Chemical processes in the upper atmosphere can affect the amount of atmospheric ozone that shields life at the surface from most of the Sun's harmful UV radiation. Each year, a "hole" of thinning atmospheric ozone expands over Antarctica, sometimes extending over populated areas of South America and exposing them to increased levels of harmful UV rays. The Dutch Ozone Monitoring Instrument (OMI) onboard NASA's Aura satellite measures amounts of trace gases important to ozone chemistry and air quality. The image above shows the amount of atmospheric ozone in Dobson Units-the common unit for measuring ozone concentration. These data enable scientists to estimate the amount of UV radiation reaching the Earth's surface and forecast high-UV-index days for public health awareness.

ULTRAVIOLET LIGHT FROM STARS

The Lyman-Alpha Mapping Project (LAMP) onboard the Lunar Reconnaissance Orbiter can peer into permanently shaded craters on the moon by sensing the faint reflections of UV light coming from distant stars.

AURORAE

Aurorae are caused by high-energy waves that travel along a planet's magnetic poles, where they excite atmospheric gases and cause them to glow. Photons in this high-energy radiation bump into atoms of gases in the atmosphere causing electrons in the atoms to excite, or move to the atom's upper shells. When the electrons move back down to a lower shell, the energy is released as light, and the atom returns to a relaxed state. The color of this light can reveal what type of atom was excited. Green light indicates oxygen at lower altitudes. Red light can be from oxygen molecules at a higher altitude or from nitrogen. On Earth, aurorae around the north pole are called the Northern Lights.

JUPITER'S AURORA

The Hubble Space Telescope captured this image of Jupiter's aurora in ultraviolet wrapping around Jupiter's north pole like a lasso.

This unusual false-color image shows how the Earth glows in ultraviolet (UV) light. The Far UV Camera/Spectrograph deployed and left on the Moon by the crew of Apollo 16 captured this image. The part of the Earth facing the Sun reflects much UV light and bands of UV emission are also apparent on the side facing away from the Sun. These bands are the result of aurora caused by charged particles given off by the Sun. They spiral towards the Earth along Earth's magnetic field lines.

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Citation

APA

National Aeronautics and Space Administration, Science Mission Directorate. (2010). Ultraviolet Waves. Retrieved [insert date - e.g. August 10, 2016], from NASA Science website: http://science.nasa.gov/ems/10_ultravioletwaves

MLA

Science Mission Directorate. "Ultraviolet Waves" NASA Science. 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov/ems/10_ultravioletwaves

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Bees, along with some birds, reptiles andother insects, can see near-ultraviolet lightreflecting off of plants. Bug zappers attractinsects with ultraviolet light to lure themto the trap. What is UV Light? Ultraviolet (UV) light has shorter wavelengths than visible light. Although UV waves are invisible to the human eye, some insects, such as bumblebees, can see them.

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Ultraviolet Radiation: How It Affects Life on Earth : Feature Articles

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Stratospheric ozone depletion due to human activities has resulted in an increase of ultraviolet radiation on the Earth's surface. The article describes some effects on human health, aquatic ecosystems, agricultural plants and other living things, and explains how much ultraviolet radiation we are currently getting and how we measure it.

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SOURCES OF GAMMA RAYS

Gamma rays have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum. They are produced by the hottest and most energetic objects in the universe, such as neutron stars and pulsars, supernova explosions, and regions around black holes. On Earth, gamma waves are generated by nuclear explosions, lightning, and the less dramatic activity of radioactive decay.

DETECTING GAMMA RAYS

Unlike optical light and x-rays, gamma rays cannot be captured and reflected by mirrors. Gamma-ray wavelengths are so short that they can pass through the space within the atoms of a detector. Gamma-ray detectors typically contain densely packed crystal blocks. As gamma rays pass through, they collide with electrons in the crystal. This process is called Compton scattering, wherein a gamma ray strikes an electron and loses energy, similar to what happens when a cue ball strikes an eight ball. These collisions create charged particles that can be detected by the sensor.

GAMMA RAY BURSTS

Gamma-ray bursts are the most energetic and luminous electromagnetic events since the Big Bang and can release more energy in 10 seconds than our Sun will emit in its entire 10-billion-year expected lifetime! Gamma-ray astronomy presents unique opportunities to explore these exotic objects. By exploring the universe at these high energies, scientists can search for new physics, testing theories and performing experiments that are not possible in Earth-bound laboratories.

If we could see gamma rays, the night sky would look strange and unfamiliar. The familiar view of constantly shining constellations would be replaced by ever-changing bursts of high-energy gamma radiation that last fractions of a second to minutes, popping like cosmic flashbulbs, momentarily dominating the gamma-ray sky and then fading.

NASA's Swift satellite recorded the gamma-ray blast caused by a black hole being born 12.8 billion light years away (below). This object is among the most distant objects ever detected.

COMPOSITION OF PLANETS

Scientists can use gamma rays to determine the elements on other planets. The Mercury Surface, Space Environment, Geochemistry, and Ranging (MESSENGER) Gamma-Ray Spectrometer (GRS) can measure gamma rays emitted by the nuclei of atoms on planet Mercury's surface that are struck by cosmic rays. When struck by cosmic rays, chemical elements in soils and rocks emit uniquely identifiable signatures of energy in the form of gamma rays. These data can help scientists look for geologically important elements such as hydrogen, magnesium, silicon, oxygen, iron, titanium, sodium, and calcium.

The gamma-ray spectrometer on NASA's Mars Odyssey Orbiter detects and maps these signatures, such as this map (below) showing hydrogen concentrations of Martian surface soils.

GAMMA RAY SKY

Gamma rays also stream from stars, supernovas, pulsars, and black hole accretion disks to wash our sky with gamma-ray light. These gamma-ray streams were imaged using NASA's Fermi gamma-ray space telescope to map out the Milky Way galaxy by creating a full 360-degree view of the galaxy from our perspective here on Earth.

A FULL-SPECTRUM IMAGE

The composite image below of the Cas A supernova remnant shows the full spectrum in one image. Gamma rays from Fermi are shown in magenta; x-rays from the Chandra Observatory are blue and green. The visible light data captured by the Hubble space telescope are displayed in yellow. Infrared data from the Spitzer space telescope are shown in red; and radio data from the Very Large Array are displayed in orange.

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Citation

APA

National Aeronautics and Space Administration, Science Mission Directorate. (2010). Gamma Rays. Retrieved [insert date - e.g. August 10, 2016], from NASA Science website: http://science.nasa.gov/ems/12_gammarays

MLA

Science Mission Directorate. "Gamma Rays" NASA Science. 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov/ems/12_gammarays

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Brighter colors in the Cygus region indicate greater numbers of gamma rays detected by the Fermi gamma-ray space telescope. Credit: NASA/DOE/International LAT Team SOURCES OF GAMMA RAYS Gamma rays have the smallest wavelengths and the most energy of any wave in the electromagnetic spectrum.

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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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National Aeronautics and Space Administration, Science Mission Directorate. (2010). X-Rays. Retrieved [insert date - e.g. August 10, 2016], from NASA Science website: http://science.nasa.gov/ems/11_xrays

Science Mission Directorate. "X-Rays" NASA Science. 2010. National Aeronautics and Space Administration. [insert date - e.g. 10 Aug. 2016] http://science.nasa.gov/ems/11_xrays

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X-RAYS AND ENERGY X-rays have much higher energy and much shorter wavelengths than ultraviolet light, and scientists usually refer to x-rays in terms of their energy rather than their wavelength. This is partially because x-rays have very small wavelengths, between 0.03 and 3 nanometers, so small that some x-rays are no bigger than a single [...]

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Remember that when you listen to the radio, watch TV, or cook dinner in a microwave oven, you are using electromagnetic waves. Radio waves, television waves, and microwaves are all types of electromagnetic waves. They only differ from each other in wavelength. Waves in the electromagnetic spectrum vary in size from very long radio waves the size of buildings, to very short gamma-rays smaller than the size of the nucleus of an atom. The electromagnetic spectrum includes X-rays.

As the wavelengths of light decrease, they increase in energy. X-rays have smaller wavelengths and therefore higher energy. We usually talk about X-rays in terms of their energy rather than wavelength. This is partially because X-rays have very small wavelengths!

Roentgen's wife's hand

X-rays were first discovered in 1895 by Wilhelm Conrad Roentgen, a German scientist who found them quite by accident.

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. Roentgen called it "X" to indicate it was an unknown type of radiation.

The Earth's atmosphere is thick enough that virtually no X-rays are able to come through from outer space all the way to the Earth's surface. This is good for us but also bad for astronomy - we have to put X-ray telescopes and detectors on satellites! We cannot do X-ray astronomy from the ground.

How do we "see" using X-ray light?

What would it be like to see X-rays? Well, we wouldn't be able to see through people's clothes, no matter what the ads for X-ray glasses tell us! If we could see X-rays, we could see things that either give off X-rays or stop their transmission. Our eyes would be like the X-ray film used in hospitals or dentist's offices. X-ray film "sees" X-rays, like the ones that travel through your skin. It also sees shadows left by things that the X-rays can't travel through (like bones or metal).

When you get an X-ray taken at a hospital, X-ray sensitive film is put on one side of your body, and X-rays are shot through you. At a dentist, the film is put inside your mouth, on one side of your teeth, and X-rays are shot through your jaw, just like in this picture. It doesn't hurt at all - you can't feel X-rays.

X-ray of a tooth

Because your bones and teeth are dense and absorb more X-rays then your skin does, silhouettes of your bones or teeth are left on the X-ray film while your skin appears transparent. Metal absorbs even more X-rays - can you see the filling in the image of the tooth

When the Sun shines on us at a certain angle, our shadow is projected onto the ground. Similarly, when X-ray light shines on us, it goes through our skin, but allows shadows of our bones to be projected onto and captured by film.

This is an X-ray photo of a 1-year-old girl. Can you see the shadow of what she swallowed?

X-ray of 1-year-old showing a pin that she swallowed

We use satellites with X-ray detectors on them to do X-ray astronomy. In astronomy, things that give off X-rays (like black holes) are like the dentist's X-ray machine, and the detector on the satellite is like the X-ray film.

What does X-ray light show us?

Many things in space give off X-rays, among them are black holes, neutron stars, binary star systems, supernova remnants, stars, the Sun, and even some comets!

The Earth glows in many kinds of light, including the energetic X-ray band. Actually, the Earth itself does not glow - only aurora produced high in the Earth's atmosphere. These aurora are caused by charged particles from the Sun.

X-ray image of Earth (Credit: Polar, PIXIE, NASA)

To the left is the first picture of the Earth in X-rays, taken in March, 1996 with the orbiting Polar satellite. The area of brightest X-ray emission is red. The energetic charged particles from the Sun that cause aurora also energize electrons in the Earth's magnetosphere. These electrons move along the Earth's magnetic field and eventually strike the Earth's ionosphere, causing the X-ray emission. These X-rays are not dangerous because they are absorbed by lower parts of the Earth's atmosphere.

Many things in deep space give off X-rays. Many stars are in binary star systems - which means that two stars orbit each other. When one of these stars is a black hole or a neutron star, material is pulled off the normal star. This materials spirals into the black hole or neutron star and heats up to very high temperatures. When something is heated to over a million degrees, it will give off X-rays

Learn more about X-rays!

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NASA - National Aeronautics and Space Administration

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Remember that when you listen to the radio, watch TV, or cook dinner in a microwave oven, you are using electromagnetic waves. Radio waves, television waves, and microwaves are all types of electromagnetic waves. They only differ from each other in wavelength.

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As a group, take a photo add to the schoology discussion on the EM spectrum and write a six word story about you have found so far?

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As a group, take a photo add to the schoology discussion on the EM spectrum and write a six word story about you have found so far?

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As a group, take a photo add to the schoology discussion on the EM spectrum and write a six word story about you have found so far?

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As a group, take a photo add to the schoology discussion on the EM spectrum and write a six word story about you have found so far?

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As a group, take a photo add to the schoology discussion on the EM spectrum and write a six word story about you have found so far?

# data[].attributes.body
As a group, take a photo add to the schoology discussion on the EM spectrum and write a six word story about you have found so far?