Astronomy 123 Basics   Light and Electromagnetic Radiation

revised February 16, 2007, jeb

• We learn about the stars by studying the electromagnetic radiation that they emit.
• Light is one particular type of electromagnetic radiation.
• The other types of electromagnetic radiation are:
• radio
• infrared
• ultraviolet
• X rays
• Gamma rays
• Electromagnetic radiation is a wave with a wavelength and an amplitude.
• The frequency of a wave is related to its velocity and wavelength through the formula
• wavelength x frequency = velocity
• Since electromagnetic radiation (or waves) travel at the speed of light (300,000 kilometers/second) we have a relationship between wavelength and frequency.
• The electromagnetic spectrum ranges from radio waves at one extreme to gamma rays at the other extreme.
• Radiation is composed of "photons" (packets of electromagnetic radiation)
  • the "photons" have energies related to the "color" or wavelength
    • short wavelengths -> higher energies
      • like gamma rays
    • long wavelengths -> lower energies
      • like radio waves
• Visible light can be split into its components by a prism.
  • the bending of light in going through the prism results from REFRACTION
  • long wavelengths (red) are refracted less, than short wavelengths (blue and violet)
• The entire electromagnetic spectrum shows the frequencies and wavelengths of the types of electromagnetic radiation.
• The atmosphere blocks much of the electromagnetic radiation from space.  There are "windows" of transparency in the radio and visible parts of the spectrum.

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