Telescopes

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Telescopes
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Telescopes

• Two kind of telescopes
• Reflector
• Mirrors
• Refractor
• lenses

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Telescopes

• Reflectors are used more than refractors.
• Refractors have chromatic aberrations.
• Reflectors and refractors both have spherical
  aberrations.

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Telescopes

• Disadvantages of refractors
• Chromatic aberration
• Absorption of IR and UV is severe
• Large lens-heavy and deforms under own weight
• Two surfaces must be machined and polished

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Telescopes

• Limits to size of reflectors
• cost
• Slow process
• Imperfection possible
• Weight
• Sagging due to weight
• Cools and heats unevenly

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Telescopes

• Solutions for reflectors
• Active optics
• Computer controlled hexagon segments
• interferometry

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Telescopes

• Computer controlled telescopes
• CCD cameras (charged coupled device)

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Visible wavelength telescopes

• European Southern Observatory
• Chile
• 16-m effective diameter
• 4 (8-m) diameter mirrors

• McDonald Observatory (Hobby-Eberly)
• Mt. Fowlkes, Texas
• 11-m diameter, 9-m effective dia.
• 91 hexagon segments

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Visible wavelength telescopes

• KECK
• Mauna Kea, Hi
• 2 (10-m) effective diameter
• 36 hexagon segments each 1.8-m wide

• NOAO
• Mauna Kea, Hi Cerro Tololo, Chile
• 8 meter effective diameter

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Radio Telescopes

• Karl Jansky at Bell Labs in 1931
• Father of Radio Astronomy

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Space Telescopes

• Some radiation is absorbed by the atmosphere.
• We need to place telescopes in space for these
  wavelengths.
• We have telescopes that can see the entire
  electromagnetic spectrum.

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Space telescopes(Microwave)

• COBE cosmic background explorer
• Can learn about
• Temperature of space
• Cool dark dust clouds

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Space Telescopes (Infrared)

• Infrared Astronomical Satellite
• Can learn about
• Planets
• Comets
• Forming stars

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Space telescopes(visible)

• Hubble Space telescope (HST)
• 2.4 m diameter mirror
• Unique in space
• Not affected by atmosphere

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Space Telescopes (Ultraviolet)

• Can learn about
• Hot stars
• Hot gas

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Space Telescopes (X-ray)

• Can learn about
• Very hot regions in stars
• Violent events such as matter smashing onto a
  neutron star

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Space Telescopes (Gamma-ray)

• Compton Gamma Ray Observatory
• Can learn about
• Hottest and most violent events
• Exploding stars
• Erupting galaxies
• Neutron stars
• Black holes

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Radio Telescopes

• Value of Radio Astronomy
• Observe 24 hours a day
• Can see through cloudy skies
• Opens up a whole new window on the universe
• Clouds of cool hydrogen
• Active galaxies
• Can be placed anywhere where space is available

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Radio Telescopes

• One disadvantage
• Weak signals
• Need large telescopes
• Or need interferometers

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Radio Telescopes

• Largest steerable
• Green Bank, West Virginia
• Diameter 100m stands higher than Statue of
  Liberty

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Radio Telescopes

• Arecibo, Puerto Rico

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Radio Telescopes

• Very Large Array (VLA)
• New Mexico desert
• 27 Radio dishes
• Y-shaped set of tracks