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