Lecture 13

2. Lecture 13 ASTR 111 – Section 002

3. Optics and Telescopes

4. If it is before 9 am, please do not sit in the last two rows.

5. Outline • Quiz Discussion • Finish a few slides from last lecture • Optics (Reading is Chapter 6)

6. Quiz Discussion • 75% Computing your grade – will not cover in class • 66% Photons through a hole – will cover in class • Can we finish going over lecture 12 in class? • Are you going to post the answers to lecture 12? • When is the next exam scheduled? • What acts as a nature's prism to create a rainbow in the sky?   • If enacted, will clickers be mandatory?   • I think we should use iclickers. Wouldn't it be easier than texting? • How many pets do you really have? • Can you review fully before the next exam? • Does it bother you when people come 45 minutes late to lecture and slam there stuff around and make a lot of noise? Because it really bothers me.   • Why is this class getting exponentially more difficult?

7. Next Exam • Next Tuesday. • Same format as before. I will review on Tuesday and you can take it on Tues. or Wed. • There will be a quiz due on Tuesday at 9am. The quiz will cover material covered last lecture and today’s lecture (lecture 12 and lecture 13 slides).

8. Why are there so many telescopes in Hawaii? Why is our best most famous telescope orbiting Earth and not in Hawaii? What is the difference between optical and digital magnification (zoom)? How and when (but not why) does light (and other forms of electromagnetic radiation) bend? How does a telescope work? What is the difference between magnification and light-gathering power? Key Questions

9. side note: What is the difference between optical and digital zoom?

10. side note: What is the difference between optical and digital zoom? Same amount of information if I just expand the original T

11. Practical note: What is the difference between optical and digital zoom? Much more information (detail) T

12. Therefore • You can create a digital zoom effect by taking a digital picture and expanding it (with photoshop, etc.) • You can’t squeeze out more detail from the image (that is, increase the optical resolution), contrary to what you see on TV

13. How much larger is a raw image of 800x800 pixels than one with 1600x1600 pixels?

14. 1600x1600 = 2,560,000 versus • 800x800 = 640,000 4x 1600 800

15. Which sounds better in an advertisement: • 1600 x 1600 or over two million megapixels?

16. Can explain lots about telescopes and other devices with only three optics principles

19. Principle 1 • Light rays from distant object are nearly parallel

20. Principle 1 • Light rays from distant object are nearly parallel Collector

21. Principle 2 • Light reflects off a flat mirror in the same way a basket ball would bounce on the floor (angle of incidence, i = angle of reflection, r)

22. Principle 3 prep

23. What happens, a, b, or c? Axle and wheel from toy car or wagon Sidewalk • As a beam of light passes from one transparent medium into another—say, from air into glass, or from glass back into air—the direction of the light can change • This phenomenon, called refraction, is caused by the change in the speed of light Grass

24. What happens, a, b, or c? Axle and wheel from toy car or wagon Sidewalk • As a beam of light passes from one transparent medium into another—say, from air into glass, or from glass back into air—the direction of the light can change • This phenomenon, called refraction, is caused by the change in the speed of light Grass

25. Principle 3 • Light changes direction when it moves from one media to another (refraction). Use wheel analogy to remember which direction normal 90o Low index (e.g., air) Higher index (e.g. water)

26. Principle 3a • Light changes direction when it moves from one media to another (refraction). Use wheel analogy to remember which direction normal 90o Low index (e.g., air) Higher index (e.g. water)

27. Principle 3b • Same principle applies when going in opposite direction normal 90o Low index (e.g., air) Higher index (e.g. water)

28. Which normal does it bend towards/away from? • Draw un-bent path and then bend a little towards or away from the nearest normal line.

29. Principle 3c • At interface light diffracts and reflects (you can see your reflection in a lake and someone in lake can see you) These angles are equal i r Low index (e.g., air) Higher index (e.g. water)

30. What happens to each beam? A B C A B C A B C

31. What happens? zoom box ? ? ?

32. nearly flat when zoomed in zoom box contents zoom box contents

33. 90o normal To figure out path, draw normal and un-bent path. zoom box contents zoom box contents

34. 90o normal Bends toward the normal. nearly flat when zoomed in zoom box contents zoom box contents

35. What happens? ? ? ? zoom box

36. zoom box contents

37. 90o zoom box contents

38. 90o zoom box contents

40. The Lines Converge F Input parallel lines converge to focal point

41. What happens to the beams here? F

42. F And parallel lines go out when source at focal point

43. But you said different colors bend different amounts!?

44. But you said different colors bend different amounts!? This is chromatic aberration

45. How I remember red bends less

46. How my optometrist remembers Red light bends only a little Red light has little energy (compared to blue)

47. What happens? ?

50. ?