1 Light and Telescopes

2 Topics l The Doppler Effect l Extending Our Senses l Summary

3 The Doppler Effect

4 Fig. 2-14, p. 30

5 Doppler Effect

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

7 Extending Our Senses

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

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

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

11 Sidereus Nuncius, G. Galileo On the 7 th 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 Commandment Edited by Edmund Blair Bolles

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

13 Fig 3-27, p.45 Broadening Our Vision 1 meter1 trillionth of a meter Technology now exists that can record radiation spanning wavelengths from about 1 meter to 1 trillionth of a meter

14 Optical Telescopes

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

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

17 Light-Gathering Power: Example D 2 = 2.4 m A1A1 A2A2 D 1 = 6 x m A 1 =  (D 1 / 2) 2 A 2 =  (D 2 / 2) 2 pupil of human eye Hubble A 2 / A 1 (D 2 / D 1 ) 2 A 2 / A 1 = (D 2 / D 1 ) 2 = (2.4 / 6 x ) 2 = 1.6 x 10 5

18 Angular Resolution

19 Fig 3-5, p.37

20 Fig 3-12, p.39 Yerkes Observatory

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 p.34 Hubble Space Telescope (HST)

26

27 Radio and X-Ray Telescopes

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

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

30 Fig 3-29, p.45

31 Fig 3-30, p.46

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