Chapter 3 Book Notes

# Chapter 3 Book Notes - Astronomy 180 Chapter 3: Light and...

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Astronomy 180 Chapter 3: Light and Telescopes (Pages 62-93) I. The Nature of Light Electromagnetic radiation – radiation consisting of oscillating electric and magnetic fields, namely gamma rays, X rays, visible light, ultraviolet and infrared radiation, and radio waves II. The Nature of Light: Newton discovered that white light is not a fundamental color and debated whether light is composed of particles or waves From the time of Aristotle until the late 17 th century, people believed that white light was basic and colors were produced through a medium Isaac Newton’s experiments in the late 1600s disproved this theory Refraction – the bending of light rays when they pass from one transparent medium to another Spectrum (spectra) – the result of electromagnetic radiation passing through a prism or grating so that different wavelengths are separated White light is a mixture of colors – Isaac Newton Newton – light is composed of tiny particles of energy ; Christiaan Huygens – light travels in the form of waves (both correct) Thomas Young, in 1801, demonstrated that light is composed of waves James Clerk Maxwell unified the basic properties of electricity and magnetism, including light, into 4 equations Newton showed that sunlight is composed of all the colors of the rainbow Different colors have different wavelengths – the distance between two successive peaks in a wave ( λ ) The wavelengths of all colors are extremely small, less than a thousandth of a millimeter ( nanometer; 1 nm = 10 - 9 m) Angstrom ( Å ) 1 Å = .1 nm or 10 -10 m Visible light covers wavelengths between 400 (violet) and 700 (red) nm The shorter the wavelength, the more light that is refracted III. The Nature of Light: Light travels at a finite, but incredibly fast, speed Ole Rømer provided first evidence for the finite speed of light by using Jupiter’s moon’s eclipses It takes light 16½ minutes for visible light to traverse the diameter of Earth’s orbit (2 AU) Maxwell’s equations reveal that light waves of all wavelengths travel at the same speed in a vacuum The speed of light is approximately 299,792.458 or 3.0 x 10 5 km/s in a vacuum; light always travels slower through other mediums In 1999 scientists slowed light to 61km/hr and in 2001 they were able to momentarily stop it completely Christian Doppler pointed out in 1842 that wavelength and color are affected by motion Blueshift – a shift of all spectral features toward shorter wavelengths; the Doppler shift of light from an approaching source Redshift – the shifting to longer wavelengths of the light from remote galaxies and quasars; the Doppler shift of light from any receding source Doppler shift (Doppler effect) – the change in wavelength of radiation due to relative motion between the source and the observer along the line of sight IV. The Nature of Light: Einstein showed that light sometimes behaves as particles that carry energy

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## This note was uploaded on 04/18/2008 for the course AST 180 taught by Professor Barlow during the Fall '08 term at N. Arizona.

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Chapter 3 Book Notes - Astronomy 180 Chapter 3: Light and...

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