*Astronomers analyze light from objects in space in order to learn about the composition and movement of the objects.

After today’s lecture, you should be able to:

–    Describe the characteristics of electromagnetic radiation.

–    Explain ways of analyzing light in order to get information about stars.

–    Explain the Doppler Effect and how it gives information about the motion of stars.

*Light is a form of electromagnetic radiation, which is energy that travels in waves.

The Electromagnetic Spectrum of Radiation

*There are several different forms of radiation.

-These are arranged on a spectrum by the size of their wavelengths, from longest to shortest

-A wavelength is the distance from 1 wave crest to the next wave crest.

Types of Radiation (from longest to shortest)

  • Radio Waves = longest waves  

*least energy  (1000-1 m)

  • Microwaves (10-1 – 10-4 m)
  • Infrared (Heat) (10-4 – 10-6.5 m)
  • Visible Light = ROYGBIV → Red (longest) to Blue (shortest) (10-6.5 – 10-7 m)
  • Ultraviolet (10-7 – 10-8 m)
  • X-Rays (10-8 – 10-11 m)
  • Gamma Rays = shortest waves

*most energy  (10-11 m and smaller)

*All of these travel at the speed of light!

The Spectroscope

*White light = All colors of visible light

  • Can be broken down into the visible spectrum using a spectroscope– a tool which uses a prism to separate light into its different colors!
    • ROYGBIV = red, orange, yellow, green, blue, indigo, violet
    • Spectrum can be used by astronomers to learn more about distant stars!
  • Spectroscopes break light into 3 types of spectra:

Types of Visible Spectra

1) Continuous Spectrum

  • Shows an unbroken band of the colors of the visible spectrum
  • Indicates that its source is emitting light of all visible wavelengths.
  • Source is a form of glowing solid, liquid, or compressed gas
  • Examples:  hot filament of an electric light; molten iron; compressed gas inside stars

2) Emission Spectrum

  • Shows a series of unevenly spaced lines of different colors & brightnesses
  • Indicates that the source is only emitting light of certain wavelengths.
  • Used to identify elements found in the source object, since:
  • Each element has its own unique emission spectrum! Like a fingerprint!

3) Absorption Spectrum

  • Shows a continuous spectrum crossed by dark lines.
    • This forms when light from a glowing object passes through a cooler gas- (Like that of its atmosphere or outer layers.)
    • The lines represent the composition of the gas (or the star’s outer layers!)
  • Comparing emission and absorption spectra, scientists can determine what elements are present in the cooler gas.

The SUN as an Example:

  • Interior = hot, compressed gases = continuous spectrum
  • Outer Layers = chromosphere & photosphere
  • These are cooler than the interior.
    • Absorb some electromagnetic radiation from the interior.
    • Dark lines = elements in the outer layers!

*Absorption spectrum can also tell us about a planet’s atmospheric composition.

  • Planets shine by reflecting light from the sun.
  • Dark lines NOT found in the star’s (sun’s) spectrum are caused by elements in the planet’s atmosphere!

The Doppler Effect

*Example = A drop in pitch when a car races past.

  • As the car approaches the wavelength of the sound waves decreases (becomes shorter) = higher pitch
  • As the car moves away the wavelength of the sound waves increases (becomes longer) = lower pitch

*The Doppler Effect = works the same way for both sound (as mentioned above) & light

  • Light = Objects (ex.- star) moving toward
  • Wavelengths become shorter =blueshift
    • Light =  Objects (ex.- star) moving away
    • Wavelengths become longer = redshift

*By using this info., we can tell how objects in space are moving in relation to Earth!

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