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Observatories and Telescopes Mauna Kea, Hawaii (14,000 ft)

Observatories and Telescopes Mauna Kea, Hawaii (14,000 ft). Why do telescopes need to be located at high altitude and dry climate ?. Telescopes – Mirrors and Lenses. Telescopes are basically a large mirror ( reflecting ) or a lens ( refracting ) Consider the human eye as ‘ telescope ’

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Observatories and Telescopes Mauna Kea, Hawaii (14,000 ft)

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  1. Observatories and TelescopesMauna Kea, Hawaii (14,000 ft) Why do telescopes need to be located at high altitude and dry climate ?

  2. Telescopes – Mirrors and Lenses • Telescopes are basically a large mirror (reflecting) or a lens (refracting) • Consider the human eye as ‘telescope’ • What determines the “power” of a telescope ?

  3. Collecting Area Retina Lens Eye could be a “refracting” telescope, but the size is very small

  4. Collecting Area = Power • A = p ( d / 2)2 ; d – diameter • Diameter of the telescope indicates its power • Largest optical telescope: Keck 1 and 2, each with a mirror of 10 m diameter • Large Binocular Telescope (LBT): Ohio State, Arizona, Germany, Italy  Two 8.4 m mirrors in a binocular shaped mount • HST – Only 2.4 m, but with a huge advantage • How much more powerful than HST is the Keck (neglecting that advantage) ? • New 30m telescope on the drawing board

  5. Large Binocular TelescopeMount Graham, Arizona

  6. Large Telescopes Thirty-meter class telescopes (TMT) under construction

  7. Objective and eyepiece

  8. Telescope  Objective and Eyepiece • The main function of a telescope is to collect as much light as possible from the source, NOT to magnify an image • Need bigger and bigger telescopes! • The main mirror or lens of a telescope is called the OBJECTIVE • The Eye-Piece (small lens or mirror) is to magnify the image after it is formed from the light collected by the objective (simply change the eyepiece to magnify image)

  9. Properties of Light and Telescopes • Reflection  Mirrors • Refraction  Lenses

  10. Focus Simple Refracting Telescope Convex lens Secondary Lens (Eyepiece) Objective Lens

  11. Spheres of light from distant source  parallel rays at the observer

  12. Different speeds in different media Bending or Refraction

  13. Refraction of light beam Normal (Perpendicular) Light bends towards the perpendicular going into denser medium, and vice-versa

  14. Refraction by prism and lens

  15. Refractive Index • Speed of light slows down in a medium ! • The ratio of the speed of light in vacuum to the speed in a medium c / v = m ‘mu’ is called the Refractive Index • Material R.I. Water 1.33 Glass 2.6 • Bending of light (diffraction) depends on R.I of the medium and wavelength of light l

  16. Chromatic Aberration:Different colors at different focus Chromatic aberration affects refracting telescopes; therefore use reflecting telescopes in modern observatories

  17. Law of Reflection: Angle i = Angle r

  18. REFLECTING TELESCOPES Prime Focus Secondary Mirror Cassegrain Focus Primary Mirror

  19. Reflecting Concave Mirror

  20. Telescopic Configurations

  21. Spherical and Parabolic Mirrors

  22. Wavelength range of observatories and telescopes • Ground based telescopes can measure - Visible (4000-7000 A), - Near-IR (0.7-2 microns), 1 mm = 10000 A - Radio ( ~ 1 mm or greater) All other wavelengths blocked out by the atmosphere • Space based observatories for Gamma ray, X-ray, UV, and Far-IR astronomy

  23. Visible (Optical) and Radio “Windows” in the Atmosphere

  24. Radar and Radio Astronomy Radio telescopes (like huge satellite dish) collect radio waves from astronomical objects Radar telescope = Transmitter + Radio Telescope Doppler Radar Transmits radio waves towards an object and collects reflected radio waves; spread in signal shows distance and velocity Largest radio telescope is the Arecibo, 1000 ft diameter, in Puerto Rico No longer! 1600 ft diameter in China

  25. Radio Telescope

  26. Aracebo Radio Telescope(Puerto Rico)

  27. Rotational Speed and Doppler Shift(Line profile broadens on both the blue and red side) Doppler Radar

  28. Hubble Space Telescope

  29. Ground and HST images Resolved Unresolved

  30. Visible and IR images of Saturn

  31. Gamma-Ray View of the Sky Each wavelength band presents a different and mutually complementary view

  32. Telescope and Instruments

  33. Intensities of Lines in Absorption Spectra: Atoms absorb energy Emission spectra are a set of bright lines: atoms emit energy

  34. Observing Planets and Moons

  35. Spectra of Titan (Moon of Saturn):Methane (CH4)

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