What Is Electromagnetic Radiation

All forms of light are forms of electromagnetic radiation. Whether it is visible light the eye can detect, X-rays used by doctors to look at bones, radio waves that transmit music, or microwaves used to cook food, all are forms of electromagnetic radiation.

Radiation is produced throughout the universe when electrons, the tiny charged particles on the outer edges of atoms, make changes in their motion, usually by collisions with other rapidly moving atoms. These swift changes, similar to minuscule vibrations, produce bundles of energy called photons, which vary in energy levels and move across the universe at the speed of light.

Astrophysicists consider electromagnetic radiation to be both waves and photons, each distinct from the other. In all cases, the length of the wave is related to the energy contained in the photons; the shorter the wavelength, the higher the energy of the photons. The only difference between the various types of electromagnetic radiation is their wavelengths and the amount of energy found in their photons. Radio waves, for example, which can occasionally be miles in length, have photons with very low energies, while gamma rays, which rarely exceed one-millionth of an inch, have very high energies. As a point of comparison, the vibration energy required to produce a single gamma ray is billions of times more rapid than the vibration of a radio wave. Although this may sound like a massive amount of energy, the energy from hundreds of trillions of gamma rays would not be enough to light a single lightbulb, even for a second.

The conversion of nonvisible waves into visible pictures is now performed by complex computer software programs. Their job is to take the amplified waves, determine their individual profiles based on several characteristics, assign a numeric value, and then convert their values into dots, called pixels, which are transferred onto photographic paper. Sometimes following hours of capturing distant radio waves, thousands of numeric values are combined by computers to form one dazzling color photograph of tens of thousands of pixels depicting an expansive galaxy swirling in a dense, gaseous region billions of light-years away.

The Big Ear

As the size of radio dishes grew to capture longer electromagnetic wavelengths from deeper space, a consortium of American radio astronomers stumbled across a naturally occurring concave depression in the earth's limestone surface in the mountainous jungle of Arecibo, Puerto Rico. In 1963, recognizing that this depression might be a perfect place to construct an enormous radio observatory, scientists began construction of a dish one thousand feet in diameter that was immediately dubbed "the Big Ear." Besides the natural depression, the surrounding jungle acted as a buffer to keep towns and highways at a safe distance, thereby minimizing terrestrial interference with incoming celestial signals. The giant size of the reflector is what makes the Arecibo Observatory unique. It is the largest telescope on the planet, which means it is also the world's most sensitive radio telescope. Other radio telescopes may require observing times of several hours to collect enough energy and data from a distant radio source, whereas at Arecibo such an observation may require just a few minutes.

Such a massive telescope embedded in the earth's crust has one major flaw: It cannot be aimed by rotating or tipping the dish. To resolve this problem, astrophysicists realized they would need to aim the telescope by moving the feed rather than the dish. The feed at Arecibo, which is suspended 450 feet above the dish, hangs in midair on eighteen cables. It is a bow-shaped structure 328 feet long that can be moved side to side and positioned anywhere up to twenty degrees from the vertical to focus on objects in deep space. Aiming the feed at a certain point above the dish enables radio emissions originating from a very small area of the sky in line with the feed to be accurately focused, thereby producing superb photographs.

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