CHAPTER 3 (p. 62- 68) Light
Jan 11, 2016
CHAPTER 3 (p. 62-68)Light
Only a very small range of wavelengths, 400nm to 700nm, are visible to humans.
Wavelengths are very small so astronomers use nanometers 10 -9 m or angstroms 10 -10 m
Electromagnetic Radiation
CRAB NEBULA
Optical Ultra Violet
X-Ray Radio
Multiwavelength Universe
The transparency of a material depends on the wavelength of light. Earth’s atmosphere is relatively transparent to visible light and radio waves, which are referred to as “windows” through which we can view space from a ground-based telescope.
Gamma-rays more than 108 (K) accretion disks around black
holes
X-rays 106-108 K gas in clusters of galaxies, supernova
remnants; stellar corona
Ultraviolet 104-106 K supernova remnants; very hot stars
Visible 103-104 K planets, stars, some satellites
Infrared 10-103 K cool clouds of dust and gas; planets
Radio less than 10 K radio emission produced by electrons moving in magnetic
fields
Radiation Type Temp. Source
Electromagnetic radiation • Oscillations of electric and magnetic fields• Inseparable – move in same direction• Move through empty space at the speed light (c)• c= 3.0 x 108 m/s
Models of Light
Wave Model Behaves as a transverse
wave Described by
wavelength, frequency and amplitude
Explains how light waves interfere with each other
The Doppler Effect
Sources moving toward the observer squeeze light waves in front of them, causing them to be shorter. We call this a
blueshift.
Sources moving away from the observer stretch the light waves behind them, causing them to be longer. We call this a
redshift.
Models of Light
Particle Model Energy in light is
contained in individual particles called photons
Different colors have different energy
No mass, just energy