Chapter 3

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2. Chapter 3 Telescopes The Tools of Astronomy 2

3. Hotel Mauna Kea http://www.youtube.com/watch?v=XPdTlHK1h_0 Charles Hakes Fort Lewis College 3 3

4. Outline • Test Friday • Don’t forget your green/red scantron sheets • #2 pencil(s). • Calculator (no phone calculators) • Optical Telescopes • Refractors • Reflectors • Others • Other Wavelengths 4

5. Drop-in Study Sessions • Thursday 2:30-4:30 • Use it or lose it. • Don’t forget conversion practice page • Review questions on-line also 5

6. Review • What was the most important thing you learned? • the speed of light, x-ray, gamma rays... is all the same. (~= 3.00x108 m/s) • wavelength x frequency = velocity • frequency = 1/period • Electromagnetic waves don’t need anything to move in. • There are far more types of invisible “light” than there are visible 6

7. The Speed of Light 299,792.458 km/sec (~= 3.00x108 m/s) It’s not just a good idea. It’s the law! Charles Hakes Fort Lewis College 7 7

8. History of The Speed of Light Charles Hakes Fort Lewis College 8 8

9. Figure 2.4Charged Particles Charles Hakes Fort Lewis College 9 9

10. Figure 2.5Magnetism Charles Hakes Fort Lewis College 10 10

11. Figure 2.6Electromagnetic Wave Charles Hakes Fort Lewis College 11 11

12. Figure 2.7Visible Spectrum Charles Hakes Fort Lewis College 12 12

13. Figure 2.8Electromagnetic Spectrum Charles Hakes Fort Lewis College 13 13

14. Which is correct A) period * frequency = wavelength B) velocity / period = wavelength C) velocity * frequency = wavelength D) velocity * period = wavelength 14

15. Which is correct A) period * frequency = wavelength B) velocity / period = wavelength C) velocity * frequency = wavelength D) velocity * period = wavelength 15

16. Which list is in the correct order of electromagnetic radiation frequency, going from lowest to highest? A) infrared, ultraviolet, gamma, radio B) gamma, x-ray, ultraviolet, visible C) radio, infrared, visible, ultraviolet D) radio, x-ray, ultraviolet, visible E) red, violet, blue, green 16

17. Which list is in the correct order of electromagnetic radiation frequency, going from lowest to highest? A) infrared, ultraviolet, gamma, radio B) gamma, x-ray, ultraviolet, visible C) radio, infrared, visible, ultraviolet D) radio, x-ray, ultraviolet, visible E) red, violet, blue, green 17

18. Discussion/Exercise • What is the wavelength of a microwave oven at 2.45 GHz? 18

19. What is the wavelength of a microwave oven at 2.45 GHz? A) 7.35x1017 m B) 0.735 m C) 122 m D) 0.122 m 19

20. Chapter 3Hubble Space Telescope and VLT 20

21. Figure 3.6bcPalomar Telescope 21

22. Figure 3.8Mauna Kea Observatory 22

23. Figure 3.9VLT Observatory 23

24. Figure 3.XFLC Observatory 24

25. Figure 3.XFLC Observatory 25

26. Telescopes • What is a telescope? • What does it do for you? 26

27. Telescopes • A telescope is a “light bucket” - it gathers photons. • A telescope is an imaging device - it focuses the photons. • It also magnifies, but this is less important. 27

28. Figure 3.1Reflecting Mirror 28

29. Figure 3.3Image Formation 29

30. Types of Telescopes • Refractor • Galilean • Achromatic • Apochromatic • Reflector • Newtonian • Cassegrain • Catadioptric • Schmidt Cassegrain • Maksutov Cassegrain 30

31. Figure 3.4Reflectors and Refractors 31

32. Refractors 32

33. Figure 3.2Refracting Lens 33

34. Figure 2.7Visible Spectrum 34

35. Refractors • Galilean - • Uses one positive and one negative lens. • No longer made. (except for toys = “pirate” telescope) • Very narrow field of view • Achromatic • Apochromatic 35

36. Refractors • Achromatic • Most common type of small telescope today. • The “objective” lens has two different types of glass. • Red light and green light can focus in the same spot. • Often have a “purple haze” on bright objects. • Apochromatic • Uses exotic glass or more than two lens elements. • Gets three of more colors to focus together - no more purple haze • Expensive. 36

37. Demonstration • Making a refractor telescope • Objective • Eyepiece • Mount 37

38. Reflectors • Newtonian • Parabolic mirror • Several places possible to focus the light. 38

39. Figure 3.5Reflecting Telescopes 39

40. Reflectors • Assembly Demonstration • Advantages • can make mirrors bigger (can support them from the back) • Reflection only on surface (colors focus together) • Only need one optical surface (lenses require at least two) 40

41. Telescopes • Building your own telescope can be very fun and rewarding. • You cannot build a telescope as cheaply as you can buy one. • Be sure to get good eyepieces. Half the imaging device is the eyepiece. Some can be expensive, however. 41

42. Telescopes • No telescope is good at all things. • Know what you want to observe. • The best telescope is the one that gets used the most. 42

43. Useful Parameters • Focal ratio (focal length/diameter) • Magnification (FL/fl) • maximum 50x/inch rule of thumb • or… 300x max (from the atmosphere) • Exit pupil (diameter/magnification) • 7mm max • 0.5mm min 43

44. Figure 3.7Sensitivity • Size does matter • Bigger is better! (diameter, that is) 44

45. Figure 3.6aPalomar Telescope 45

46. Figure 3.6bcPalomar Telescope 46

47. Figure 3.8Mauna Kea Observatory 47

48. Figure 3.9VLT Observatory 48

49. Telescope size • Light gathering ability is proportional to the area of the objective. • This means it is proportional to the diameter squared. • 8” telescope gathers 4 times the light of a 4” telescope. ( 8”x8”=64 sq in, 4”x4”=16 sq in ) • Photographic exposures would be 1/4 as long on the 8” as they would be on the 4” • Similarly, an 8” telescope gathers 1/4 as much light as a 16” telescope. 49

50. Size Example - Binoculars • 10x50 binoculars • “10” means - • “50” means - • How much more light can they gather than your naked eye? • eyes ~7mm diameter 50