Chapter 3 -- The Universe

Chapter 3 -- The Universe - GEO 1013 THE THIRD PLANET E. R....

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GEO 1013 – THE THIRD PLANET E. R. SWANSON – SPRING 2009 THE UNIVERSE STARS & TELESCOPES The Electromagnetic Spectrum Why do we know more about some distant stars than we do about parts of our own solar system? It is because stars, unlike some of the dark corners of our solar system, radiate energy that can be received through telescopes. Stars and other celestial objects radiate energy of a wide variety of types, necessitating a wide variety of telescopes. Various stars emit electromagnetic energy from all parts of what is known as the electromagnetic spectrum . Toward the end of the 19 th century physicists realized that energy could be transmitted in waves through a vacuum. These waves did not require a transmitting medium like waves in water, sound waves through air or earthquake waves through rock. They could travel through the void of space, and at a tremendous velocity. The conceptual model for these waves shows them to consist of both electric and magnetic fields (electromagnetism – get it?) arranged in two waves at right angles to each other with a wave motion that moves back and forth perpendicular to the direction in which the energy is being transmitted. Electromagnetic waves also come in a wide variety of wave lengths. Light is just that part of the electromagnetic spectrum sensed by the eye and even light consists of a range of wavelengths from longer wavelength red to shorter wavelength violet. The light spectrum includes red-orange-yellow-green-blue-violet (if you are from the old school and looking for indigo between blue and violet, it has been deleted). Yellow, the color most intensely emitted by the Sun, is conveniently located right in the middle of what the eye can see (a coincidence? I don’t think so.). Next to red on the longer wavelength side of the spectrum and no longer visible to humans is the infrared, the waves given off as heat. Some animals that hunt prey at night can see into the infrared as can the police in surveillance helicopters using instruments to locate criminals in the bushes at night. Microwaves are slightly longer, 1 meter to 1 millimeter in wavelength. Microwaves are transmitted by radar and the common microwave oven. Their energy is readily absorbed by water and transformed into heat. Radio waves have the longest wavelength. Radio stations produce these kinds of waves by accelerating an electron up and down their tall metal towers producing a long, tall wave. Ultraviolet is found next to light (violet light) on the shorter wavelength side of the visible spectrum. These energetic electromagnetic waves are found in the tanning and burning rays of the sun. Some objects, like the mineral fluorite, can absorb ultraviolet radiation produced by the so-called black lights and then re-radiate longer wavelength energy (light) in the visible part of the spectrum. X-rays have even shorter wavelengths and are capable of penetrating soft body tissue while gamma rays have wavelengths the size of an atom or less. Gamma rays are emitted during nuclear
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This note was uploaded on 09/09/2009 for the course GEO 301 taught by Professor Long during the Spring '07 term at University of Texas at Austin.

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Chapter 3 -- The Universe - GEO 1013 THE THIRD PLANET E. R....

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