04_Light_Matter - GEL36 SOLAR SYSTEM Lecture 4"Light Matter...

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1 GEL36 SOLAR SYSTEM Lecture 4: "Light, Matter & Spectra" (Ch. 6, 7 – read selectively! ) Goal of the Lecture: To provide explanatory context to the previous lecture on the characteristics of the sun. The principles and concepts outlined here provide the underlying fundamentals for many of the instruments used to determine the composition, temperature, density and motion of astronomical bodies. Information from this lecture will be used throughout the rest of the course. I: Electromagnetic Spectrum Newton recognized that when focused light from the sun passed through a prism, it split into the spectrum of colors that we see in a rainbow. - all prisms do is cause the different wavelengths of light to bend at different angles - the blue light is bent more than the yellow, which in turn is bent more than the red, resulting in separation of the constituent colors - a spectrum. - when he used a second prism to recombine the colors, he produced a beam of white light . Newton recognized that white light (like we get from the sun) was made up of a mixture of all the colors of the rainbow. - this revolutionized the field of astronomy. Almost everything known about the universe is derived from analyzing the light gathered by telescopes. But visible light is just one form of radiation called electromagnetic radiation . - EM radiation encompasses a spectrum of waves: gamma rays, x-rays, ultraviolet rays, visible light, infrared, microwaves, radio waves - all of these rays can be considered as waves that travel at the speed of light = 300,000 km/sec (186,000 mi/sec). - ("Speed of light" can also be called the "speed of EM radiation in a vacuum") EM waves grade into one another along a continuous spectrum of frequency and wavelength which are just ways to describe waves. - wavelength is the distance between successive peaks in a wave (measured in units of distance per cycle; ranges from <10 -12 to >10 4 meters). - frequency is the number of cycles that pass in one second (measured in cycles per second).
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2 Frequency is inversely related to wavelength, so that long wavelengths have low frequencies and short wavelengths have high frequencies - radio waves (UHF TV, VHF TV, FM & AM radio) have wavelengths measured in meters to kilometers ( radar is just a shorter wavelength form of TV & radio waves) When you use the term ‘wireless’, you’re really refering to the radio end of the EM spectrum. (don’t confuse radio waves of the EM spectrum (long wavelength light energy) with sound waves emanating from your radio – radio waves transmit the information (music, words) as EM energy through the air where it’s intercepted by antenna and converted inside the black box we call our radio into sound waves) - microwaves are EM radiation measured in mm to cm - infrared waves
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04_Light_Matter - GEL36 SOLAR SYSTEM Lecture 4"Light Matter...

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