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The Solar System

The Solar System. Optics and Telescopes. Refraction of Light. Light refracts twice but does not change in direction when passing through a ‘flat glass’. Light refracts twice but converges to a focus when passing through a curved glass. Refracting Telescope. f e. f o.

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The Solar System

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  1. The Solar System Optics and Telescopes

  2. Refraction of Light • Light refracts twice but does not change in direction when passing through a ‘flat glass’. • Light refracts twice but converges to a focus when passing through a curved glass.

  3. Refracting Telescope fe fo Magnification = fo / fe

  4. Question The magnification of any telescope can easily be increased by Using a larger objective. Using a larger eyepiece. Changing the objective to one with a shorter focal length. Changing the eyepiece to one with a shorter focal length.

  5. The Yerkes 40” Refractor (1897) The telescope tube is 19.5 meters long!

  6. Chromatic Aberration Different colors are not brought to a common focal point! • (c) Better solution: • Use mirrors instead of lenses!

  7. Question A defect in refracting telescopes caused by the inability a lens to bring light of all colors to a common focus is called 1) spherical aberration. 2) curvature of field. 3) chromatic aberration. 4) stellar aberration.

  8. Newtonian Telescope

  9. Other Reflecting Telescopes Does the presence of a secondary mirror cause a “hole” in the image?

  10. Spherical Aberration Parabolic mirror produces a point focus — but is expensive to make! Schmidt-Cassegrain Telescope

  11. 8.1 m Gemini North Cassegrain How much light does the secondary mirror “block”? 1 m Secondary 8.1 m Objective Hole in the Objective

  12. How to Buy a Pizza!

  13. … but we have a special today … two 12” pizzas for $20 ! A 16” pizza costs $15 12” 12” A1 = πR12 A1 = πR12 16” A2 = πR22 Great deal … 12.5% more pizza for 25% more cost! You just got #%&#* ‘ ed!

  14. Question A Cassegrain Telescope has a 8 m primary mirror and a 1 m secondary mirror. How much light is blocked by the secondary? 1) 1/4 2) 1/16 3) 1/64 4) none … it’s transparent

  15. Which Bucket Collects the Most Rain? 2D D How much more?

  16. Light Gathering Power The light gathering power (LGP) of a telescope is proportional to the Area of the primary mirror for a reflecting telescope or lens objective if it is a refracting telescope. • Remember: Area of a circle • in terms of Radius = πR2 • in terms of Diameter = πD2 / 4 R D LGP ~ A ~ D2

  17. Telescopes on Mauna Kea

  18. Keck Telescope (10 m) TMT (30 m)

  19. Question The diameter of the TMT currently being planned for the next decade is 30 meters. The diameter of the Keck telescope on Mauna Kea, currently the world’s largest, is 10 meters. How much more light will the TMT collect when viewing a distant object? 1) 1/3 as much. 2) 3 x as much. 3) 9 x as much. 4) the same amount.

  20. Equatorial Mounts Why use equatorial mounts? Once you point the telescope towards a star, the telescope only has to be moved about the polar axis to track the star as the Earth rotates about its axis.

  21. Diffraction of Light (a) Diameter of Aperture >> λ Rings are present but very small compared to central image (b) Diameter of Aperture ~ λ Rings are large compared to central image Size of rings ~ λ / D

  22. Angular Resolution ΔΘ Large D λ and D in meters Δθ in arcsec Small D

  23. Image of Binary Stars • Light undergoes ‘diffraction’ when it passes through an ‘aperture’ or around a barrier!

  24. Adaptive Optics • A Better Solution: • Use a ‘segmented’ mirror made of many small mirrors that can be moved by computer-controlled actuators. • Such a telescope quickly changes its shape and focus to remove smearing of image caused by ‘twinkling’.

  25. Imaging With CCD’s

  26. Arecibo Radio Telescope 305 m

  27. The VLA • LGP = 27 x (25 m2) equivalent to single dish 130 m diameter. • Operates as interferometer to achieve an angular resolution of … • Δθ = 0.04 arcsec, equivalent to single dish 36 km diameter!

  28. Transparency of Atmosphere

  29. Spitzer Space Telescope • 0.85 m Objective • Largest infrared telescope deployed in space. • Instruments cooled by 360 Liters of liquid helium. • Background is false color image of Milky Way at 100 μm.

  30. Hubble Space Telescope What follows Hubble …. 2.4 m objective – sensors for Visible, ‘near’ IR and UV

  31. James Webb Space Telescope (6.5 m)

  32. Chandra X-Ray Observatory

  33. XMM — Newton

  34. Compton Gamma Ray Observatory • Deployed by Atlantis in 1991. • Mission ended in 2000 … • Disintegrating upon re-entry into atmosphere.

  35. Sky at Visible, Radio, Infrared, X-Ray and γ-Ray Wavelengths

  36. Question Why are the Chandra and Newton x-ray telescopes and the Compton γ-ray telescope deployed in space? To protect us from alien invaders. No country on Earth would take them. Their on-board power sources are radioactive and dangerous. x-rays and γ-raysdo not penetrate Earth’s atmosphere.

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