Radio, IR, UV and X-Ray Telescopes

• What is an optical telescope?

  A telescope detecting visible light wavelengths
• What are non-optical telescopes?

  Telescopes detecting other electromagnetic wavelengths
• Name four types of non-optical telescopes.

  Radio, IR, UV, X-ray telescopes
• Why is collecting radiation from all parts of the electromagnetic spectrum important?

  It provides new information for astronomers
• What does the Crab Nebula emit strongly at all wavelengths?

  Different areas of a supernova remnant

  
• Where do radio waves, X-rays, and gamma rays appear to originate in the Crab Nebula?

  From the neutron star at its center
• What do infrared, visible, and ultraviolet wavelengths in the Crab Nebula come from?

  From the nebula surrounding the neutron star
• Why are images of astronomical objects often given 'false colour'?

  To visualize wavelengths the human eye cannot see
• What do the different wavelengths detected in the Crab Nebula indicate?

  They provide information about a star's life cycle

  
• What limits the operating wavelength range of ground-based telescopes?

  Absorption of wavelengths by Earth's atmosphere
• Which wavelengths are best observed from space?

  Gamma-rays, X-rays, ultraviolet, and infrared
• What does the graph of atmospheric opacity against wavelength show?

  Absorption of wavelengths by the atmosphere

  
• What can ground-based telescopes observe?

  All visible wavelengths and some infrared
• What are the main advantages of space-based telescopes?

  No absorption, light pollution, or atmospheric effects
• What is the wavelength range of radio telescopes?

  1 mm to 10 m
• What is the typical resolution of radio telescopes?

  $10^{-3} \text{ rad}$
• What are the main components of a radio telescope?

  A detector and parabolic dish

  
• Compare the structure, positioning, and uses of radio and optical telescopes.

  • Structure:
  • Both use parabolic surfaces
  • Radio uses a single reflector; optical uses two mirrors
  • Positioning:
  • Both can be ground-based
  • Optical must avoid atmospheric distortions
  • Uses:
  • Both detect hydrogen emission lines
  • Radio maps the Milky Way
• How does the resolving power of radio telescopes compare to optical telescopes?

  Radio telescopes have much lower resolving power
• Why do radio telescopes produce brighter images?

  They have greater collecting power due to size
• What is the wavelength range of infrared telescopes?

  700 nm to 1 mm
• What is the typical resolution of ground-based infrared telescopes?

  $10^{-3} \text{ rad}$
• Compare the structure, positioning, and uses of infrared and optical telescopes.

  • Structure:
  • Both use primary concave and secondary convex mirrors
  • IR mirrors must be kept cold
  • Positioning:
  • Ground-based IR telescopes need dry, high-altitude locations
  • Space-based IR telescopes are preferable
  • Uses:
  • Both detect visible and IR radiation
  • IR telescopes detect warm objects not visible in light
• Why are space-based infrared telescopes preferable?

  Atmosphere blocks most IR wavelengths
• What is the wavelength range of ultraviolet telescopes?

  10 to 400 nm
• What is the typical resolution of ultraviolet telescopes?

  $10^{-7} \text{ rad}$
• Compare the structure, positioning, and uses of ultraviolet and optical telescopes.

  • Structure:
  • Both use primary concave and secondary convex mirrors
  • UV mirrors must be smoother
  • Positioning:
  • UV telescopes must be in space
  • Uses:
  • Both determine chemical composition and temperatures
  • UV telescopes detect hot gas clouds and supernovae
• What is the wavelength range of X-ray telescopes?

  0.01 to 10 nm
• What is the typical resolution of X-ray telescopes?

  $10^{-6} \text{ rad}$
• Compare the structure, positioning, and uses of X-ray and optical telescopes.

  • Structure:
  • Both use parabolic mirrors
  • X-ray uses parabolic and hyperbolic mirrors
  • Positioning:
  • Both perform best in space
  • X-ray wavelengths are absorbed by the atmosphere
  • Uses:
  • X-ray telescopes provide information about visible objects
  • They observe non-visible objects and energetic events
• How does the resolving power of X-ray and gamma telescopes compare to optical telescopes?

  They have much higher resolving power
• Why do X-ray and gamma telescopes have lower collecting power than optical telescopes?

  They have smaller objective diameters
• What are the key points to remember for each type of telescope?

  • Structure, positioning, and uses
  • Comparison of resolving and collecting power
  • Importance of wavelength ranges