ELECTROMAGNETIC ENERGY When you tune your radio, watch TV, send a text message, or pop popcorn in a microwave oven, you are using electromagnetic energy. You depend on this energy every hour of every day. Without it, the world you know could not exist. Electromagnetic energy travels in waves and spans a broad spectrum from very long radio waves to very short gamma rays. The human eye can only detect only a small portion of this spectrum called visible light. A radio detects a different portion of the spectrum, and an x-ray machine uses yet another portion. NASAs scientific instruments use the full range of the electromagnetic spectrum to study the Earth, the solar system, and the universe beyond. A diagram (on the right ) of the electromagnetic spectrum showing the 7 regions of the spectrum (from longest to shortest wavelength): radio waves, microwave, infrared, visible, ultraviolet, x-ray, and gamma rays. Examples of radio waves include fm & am radio frequencies. Mircrowaves are used in microwave ovens and their lengths are about the size of a baseball. Infrared waves are much shorter – about the size of a thickness of paper. The heat energy that radiates off human and other animals is in the infrared region. Television remote controls use infrared light to communicate with the television. Visible light is the only region of the spectrum that our eyes can sense. Ultraviolet light is the higher energy radiation that can cause sunburn. Smaller than the size of a water molecule is the length of an x-ray. An x-ray image of a broken bone is actually the shadow cast by x-rays on a piece of x-ray sensitive film. Gamma rays are the shortest and highest energy wavelengths in the electromagnetic spectrum. These waves can be smaller than atomic nuclei. OUR PROTECTIVE ATMOSPHERE Our Sun is a source of energy across the full spectrum, and its electromagnetic radiation bombards our atmosphere constantly. However, the Earths atmosphere protects us from exposure to a range of higher energy waves that can be harmful to life. Gamma rays, x-rays, and some ultraviolet waves are ionizing, meaning these waves have such a high energy that they can knock electrons out of atoms. Exposure to these high-energy waves can alter atoms and molecules and cause damage to cells in organic matter. These changes to cells can sometimes be helpful, as when radiation is used to kill cancer cells, and other times not, as when we get sunburned. ATMOSPHERIC WINDOWS Image of NASA Spacecraft RHESSI (on the left ) Seeing Beyond our Atmosphere. NASA spacecraft, such as RHESSI, provide scientists with a unique vantage point, helping them see at higher-energy wavelengths that are blocked by the Earths protective atmosphere. Electromagnetic radiation is reflected or absorbed mainly by several gases in the Earths atmosphere, among the most important being water vapor, carbon dioxide, and ozone. Some radiation, such as visible light, largely passes (is transmitted) through the atmosphere. These regions of the spectrum with wavelengths that can pass through the atmosphere are referred to as atmospheric windows. Some microwaves can even pass through clouds, which make them the best wavelength for transmitting satellite communication signals. While our atmosphere is essential to protecting life on Earth and keeping the planet habitable, it is not very helpful when it comes to studying sources of high-energy radiation in space. Instruments have to be positioned above Earths energy-absorbing atmosphere to see higher energy and even some lower energy light sources such as quasars.
Posted on: Thu, 18 Dec 2014 23:15:21 +0000
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