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

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

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

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

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)