Light and Telescopes

1. Light and Telescopes

2. Topics • The Doppler Effect • Extending Our Senses • Summary

3. The Doppler Effect

4. Fig. 2-14, p. 30

5. Doppler Effect Fig. 2-14, p. 30

6. Discovery of Extrasolar Planets Fig. 2-16, p. 31

7. Extending Our Senses

8. Early Milestones • 1608 – Hans Lippershey • First telescope patent • 1609 – Galileo’s observations of celestial objects • Craters on the Moon • Sunspots • Phases of Venus • Moons of Jupiter • 1610 – Wrote 17th century best-seller: Sidereus Nuncius (The Starry Messenger)

9. Galileo’s drawing of the Moon Fig 3-1a, p.36

10. Galileo’s Observations of Jupiter Fig 3-2b, p.36

11. On the 7th day of January…..1610,….when I was viewing the constellations of the heavens through a telescope, the planet Jupiter presented itself to my view, and….I noticed a circumstance which I had never been able to notice before…..namely, that three little stars….were near the planet; and although I believed them to belong to the….fixed stars, yet they made me somewhat wonder, because they seemed to be arranged exactly in a straight line.. Galileo’s CommandmentEdited by Edmund Blair Bolles Sidereus Nuncius, G. Galileo

12. Phases of Venus Galileo’s discovery of the phases of Venus convinced him that Venus orbits the Sun and not the Earth Fig 3-3, p.37

13. Broadening Our Vision Technology now exists that can record radiation spanning wavelengths from about 1 meter to 1 trillionth of a meter Fig 3-27, p.45

14. Optical Telescopes

15. Characteristics of a Telescope • A telescope is a device to “see far as if near” • To “see far as if near” a telescope must • Gather radiation from an object (light, radio, x-rays, etc.). • How well this is done is called the telescope’s Light-Gathering Power. • Resolve details of the object. • How well this is done is called the Angular Resolution.

16. Light-Gathering Power Hubble Telescope Mirror • The amount of light gathered by a telescope is proportional to the area of the collector. • A1 is the area of device 1 • A2 is the area of device 2 • If A2 > A1, then the light-gathering power of device 2 is A2 / A1 times greater than that of device 1. 2.4 m mirror

17. Light-Gathering Power: Example pupil of human eye Hubble A1 A2 D1 = 6 x 10-3 m A1 = p (D1 / 2)2 D2 = 2.4 m A2 / A1= (D2 / D1)2 = (2.4 / 6 x 10-3)2 = 1.6 x 105 A2 = p (D2 / 2)2

18. Angular Resolution

19. Fig 3-5, p.37

20. Yerkes Observatory Fig 3-12, p.39

21. Fig 3-11, p.39

22. Fig 3-21b, p.43

23. Fig 3-13, p.40

24. Fig 3-16, p.41

25. Hubble Space Telescope (HST) p.34

27. Radio and X-Ray Telescopes

28. Karl Jansky Fig 3-33a1, p.47

29. The Very Large Array (VLA) Fig 3-36, p.49

30. Fig 3-29, p.45

31. Fig 3-30, p.46

32. Summary • Doppler Effect • Wavelengths increase, if separation between source and receiver is increasing • Wavelengths decrease, if separation between source and receiver is decreasing • Telescopes • Gather as much radiation as possible • Resolve as much detail as possible • Now span the entire spectrum from gamma-rays to radio-waves