Chapter 3 Book Notes

What is light • nuclear fusion converts a bit of

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Unformatted text preview: What is light? • Nuclear fusion converts a bit of the mass in hydrogen nuclei into light that ultimately flies through space until it hits something • Light is an electromagnetic wave, that is, a wave that can cause charged particles (such as electrons) to move up and down • Light is characterized by a wavelength and a related frequency • Light travels through empty space at the same speed • Light has properties that make it act like lots of individual particles called photons, that can exert pressure, knock individual electrons out of atoms, or cause molecules to start rotating and vibrating • Electromagnetic spectrum • Visible light • Infrared – light with wavelengths somewhat longer than red light • Radio waves – longest-wavelength light • Region near border between infrared and radio waves, where wavelengths range from micrometers to centimeters are called microwaves • Ultraviolet – shorter than blue light • Shorter wavelengths – X rays • Shortest-wavelengths – gamma rays • Spectroscopy – involves collecting light through a telescope, then dispersing it into a spectrum in much the same way a prism disperses white light into a rainbow of color • Spectral lines – bright or dark lines • Conclusion: Spectroscopy has therefore allowed us to determine the composition of planets, stars, and even very distant galaxies. How did the nebular model win out over competing models? • Orderly motions of large bodies • Two major types of planets • Small bodies • Exceptions to the rules • Close-counter hypothesis did not work • Conclusion: If the close encounter hypothesis had been correct, then other planetary systems would have been exceedingly rare. Why isn’t the nebular model set in stone? • There are the extrasolar planets with their surprising orbits • There are new observations of young star systems • Conclusion: The nebular theory explains so much so well that the basic concept stands on extremely solid ground. However, much remains to be learned about its details, and that makes it an exciting and ongoing topic of scientific research....
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What is light • Nuclear fusion converts a bit of the mass...

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