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Modern Physics
ULTRAVIOLET LIGHT FROM OUR SUN
Bees, along with some birds, reptiles and other insects, can see near-ultraviolet light reflecting off of plants. Bug zappers attract insects with ultraviolet light to lure them to the trap.
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.
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.
Ultraviolet Radiation
Ultraviolet Light
Ultraviolet light is a form of radiation which is not visible to the human eye. It's in an invisible part of the "electromagnetic spectrum".
Radiated energy, or radiation, is given off by many objects: a light bulb, a crackling fire, and stars are some examples of objects which emit radiation. The type of radiation being emitted depends on the temperature of the object. A coal glowing red in a barbecue is cooler than our Sun, which appears yellow, which is cooler still than some stars which appear bright white.
If a prism is used to break-up the radiated light from an object into it's component colors, the "visible light" which our eyes can see makes up only a small part of the total spectrum. Visible light runs from the familiar blue to green to yellow to orange to red. Red light is the least energetic of the colors of visible light, and blue is the most energetic. Beyond the red end of the visible part of the spectrum lies the infrared and radio radiation. Infrared "light" is familiar to us as heat, while radio waves are used for TV and radio broadcasts.
Beyond the blue end of the visible spectrum lies ultraviolet light, X-rays and gamma-rays. All of the X-rays, gamma-rays and ultraviolet light emitted by stars are absorbed by the Earth's atmosphere. That is why we need to send our telescopes into space (such as Astro-2 !) in order to measure the ultraviolet light from stars and galaxies. Many scientists are interested in studying the invisible universe of ultraviolet light, since the hottest and most active objects in the universe give off large amounts of ultraviolet energy.
What is an Angstrom?
Radiation travels in waves. Scientists use the length of the wave (the distance between peaks) to define the energy of the radiation. Astronomers measure this length in "angstroms," a unit of measure equal to 1 hundred-millionth of a centimeter. It's a convenient shorthand to avoid writing lots of zeroes when talking about the wavelengths of light. In everyday terms, a sheet of paper is approximately 1,000,000 angstroms thick. The ultraviolet portion of the spectrum being studied by Astro-2 covers the portion of the spectrum from about 900 angstroms to about 3,000 angstroms. Visible light, on the other hand, covers the range from 4,000 to 8,000 angstroms.
What is Radiation
Electromagnetic Spectrum
Scientists have found that many types of wave can be arranged together like the notes on a piano keyboard, to form a scale.
The 'low notes' have a low frequency and a long wavelength.
The 'high notes' have a high frequency and a short wavelength.
When we say "wave", you might think of a wave on the sea. There, it's nice and obvious what's going on - the surface of the sea is vibrating up and down.
With a sound wave, it's the air particles that are vibrating.
So what's vibrating when an electromagnetic wave passes by?
That's not so easy.
Electromagnetic waves are vibrations of magnetic and electric fields. So they don't need air in order to travel. They don't need anything to be there at all.
The Electromagnetic Spectrum
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.
The electromagnetic spectrum from lowest energy/longest wavelength (at the top) to highest energy/shortest wavelength (at the bottom). (Credit: NASA's Imagine the Universe)
Radio: Your radio captures radio waves emitted by radio stations, bringing your favorite tunes. Radio waves are also emitted by stars and gases in space.
Microwave: Microwave radiation will cook your popcorn in just a few minutes, but is also used byastronomers to learn about the structure of nearby galaxies.
Infrared: Night vision goggles pick up the infrared light emitted by our skin and objects with heat. In space, infrared light helps us map thedust between stars.
Visible: Our eyes detect visible light. Fireflies, light bulbs, and stars all emit visible light.
Ultraviolet: Ultraviolet radiation is emitted by the Sun and are the reason skin tans and burns. "Hot" objects in space emit UV radiation as well.
X-ray: A dentist uses X-rays to image your teeth, and airport security uses them to see through your bag. Hot gases in the Universe also emit X-rays.
Gamma ray: Doctors use gamma-ray imaging to see inside your body. The biggest gamma-ray generator of all is the Universe.
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, calledphotons, 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.
Properties of Electromagnetic Waves
Quantum Mechanics-Light Spectrum
Background Radiation
Cosmic background radiation is electromagnetic radiation from the sky with no discernible source. The origin of this radiation depends on the region of the spectrum that is observed. One component is the cosmic microwave background radiation. This component is redshifted photons that have freely streamed from an epoch when the Universe became transparent for the first time to radiation.
The natural radiation that is always present in the environment. It includes cosmic radiation which comes from the sun and stars, terrestrial radiation which comes from the Earth, and internal radiation which exists in all living things. The typical average individual exposure in the United States from natural background sources is about 300 millirems per year.