1. Telescopes Amateur and Professional

2. Galileo 1609

3. The Moon as a World

4. Jupiter has Moons

6. Refracting telescopes

8. Long focus refractors were awkward but suffered less from chromatic aberration

9. Isaac Newton’s reflecting telescope Mirrors do not have chromatic aberration

10. Reflecting telescope Objective mirrors instead of lenses

11. Three Powers Magnifying Resolving Light Gathering

12. Magnifying Power Ability to make objects appear larger in angular size One can change the magnifying power of a telescope by changing the eyepiece used with it Mag Power = focal length of objective divided by the focal length of the eyepiece

13. Resolving Power Ability to see fine detail Depends on the diameter of the objective lens or mirror

14. Light Gathering Power The ability to make faint objects look brighter Depends on the area of the objective lens or mirror Thus a telescope with an objective lens 2 inches in diameter has 4 times the light gathering power of a telescope with a lens 1 inch in diameter

15. Herschel & Lord Rosse

16. 19 th century: epoch of the large refractors

17. Refracting telescopes Vienna Lick

18. Yerkes Observatory Largest refracting telescope with a one meter objective

19. 20 th century Large Reflectors Come of Age Mount Wilson Observatory 1.5m (1908) and 2.5m (1918)

20. Palomar 5-m (entered operation in 1948)

21. 4 meter Reflecting telescope

22. Objective Mirror

23. Dome of 4 meter Kitt Peak

24. Keck Telescopes

25. SOAR Telescope 4.1 meter

26. SOAR Telescope -- Cerro Pachon

27. SOAR Observing Room

28. SOAR Image of the planetary nebula NGC 2440

29. MSU Campus Observatory

30. Boller & Chivens reflecting telescope with a 24- inch objective mirror

31. More on resolution Eagle-eyed Dawes The Dawes Limit R = 4.56/D Where R = resolution in seconds of arc D = diameter of objective in inches More appropriate for visible light and small telescopes

32. A more general expression for the theoretical resolving power Imagine that star images look like Airy disks

33. Minimum Angle that can be resolved R = 1.22 x 206,265 / d R = resolution in seconds of arc  = wavelength of light d = diameter of the objective lens or mirror Note that the wavelength of light and the diameter of the objective should be in the same units

34. Examples For Visible light around 500nm Our 24-inch telescope R = 0.20 seconds This may be compared with the Dawes limit of 0.19 seconds But with large ground-based telescopes it is difficult to achieve this

35. Astronomical “seeing” Blurring effect of looking through air Causes stars to twinkle and planetary detail to blur –At the SOAR site: good seeing means stellar images better than about 0.7 seconds of arc –In Michigan, good seeing means better than about 3 seconds of arc –Not to be confused with good transparency

36. Bad seeing on this side Good seeing on this side

37. Electromagnetic Spectrum

38. Radio Telescopes Arecibo

39. Very Large Array

40. Radio telescope resolution = 1m d = 100m R = 2500 seconds = 42 minutes! Even though radio telescopes are much bigger, their resolving power is much worse than for optical telescopes Interferometric arrays get around this

41. Very Large Array

42. Interferometry Size of array = 10 km for a VLA This becomes the effective d Now R becomes 25 secsec for a 1-m wavelength For VLBI (very long baseline interfeormetry) the d = 10,000km and R = 0.025 seconds

43. Observing from space No clouds Perfect seeing Can see wavelengths of light blocked by the earth’s atmosphere

44. Hubble Space Telescope

48. Rooftop telescopes