1. Chapter 6 Astronomical Instruments

2. Ch. 3: Why do we need telescopes?
Humans can only see 6000 stars at night and cannot resolve (discern) the detail of objects in the sky if they are too close together.
Humans also cannot see anything but visible light.
We also need some way to record images, like in photography.

3. A Reflecting Mirror brings light to a focus

4. A Refracting Lens can form an image by using the principle of the refraction of light see this link for a marching band analogy

5. A Refracting Lens can be thought of as being built up from a collection of prisms that deviate the light, so that it comes to a focus.

6. Refraction of light occurs when light passes from one type of material into another, in which the speed of light is different.

7. Image Formation can also occur with a concave mirror

8. Two types of Telescope: Reflectors and Refractors

9. Refractors are no longer used for much research
The Yerkes observatory
(near Chicago) has the
largest-ever refractor,
with a 40 inch diameter
lens. See their web site.

10. Types of Reflecting Telescopes

11. The Palomar Telescope was the largest for many years

12. Palomar Telescope (notice the person near the focus)

13. Telescopes should be large to give lots of sensitivity to dim light
Longer exposures also
produce better images.
But you have to quit
before dawn, so the
exposure time of the photo
is obviously limited.

14. Mauna Kea Observatory in Hawaii

15. Keck telescopes on Mauna Kea, Hawaii

16. Keck telescopes – cutaway view (website)

17. Very Large Telescopes Observatory in Chile

18. Telescopes on the Canary Islands (Atlantic Ocean)

19. Telescopes on Kitt Peak (near Tucson, AZ)

20. Reflectors can have larger apertures than Refractors

21. Types of Reflecting Telescopes

22. Resolution is critical for seeing image detail

23. Diffraction is an effect that limits resolution in images

24. Atmospheric Turbulence is reduced at high altitudes

25. CCD Chips are used, similar to those in your digital camera

26. Image processing can sharpen an image, though not quite like you see in some of the spy shows on TV

27. Active Optics are used in the Keck telescopes and VLT (web)
Without active optics With active optics

28. Adaptive Optics use a laser beam as a “guide star” and continually change the shape of the mirror to compensate for atmospheric turbulence and distortion.

29. The Hubble Space Telescope

30. The Hubble Space Telescope has several cameras

31. Telescopes are available for most of the Electromagnetic Spectrum
Radio (and microwave), infrared, visible, ultraviolet, X-ray, Gamma ray

32. Electromagnetic Waves
Waves are characterized by their
Wavelength – distance between crests
Frequency – number of cycles per second
Amplitude – displacement from equilibrium
Type – transverse, longitudinal, etc.
Polarization – direction of electric field in an electromagnetic wave
Dan Russell demos here for class discussion

33. Zoom in
next slide

35. Frequency f (in Hz) Wavelength l

36. Radio telescopes usually “look” at microwave signals
Frequencies of some radio waves used in commercial service in the US (you don’t need to know these):
AM radio: 535 kHz to 1610 kHz
FM radio: 88 MHz to 108 MHz
TV channels 2-6 are MHz (before the digital era)
TV channels 7-13 are MHz
TV channels are MHz (these are changing)
Microwave oven: GHz
Cell phone: MHz or MHz (PCS)
Most radio astronomy uses much higher frequencies
Parabolic reflectors are often used for higher frequencies

37. Radio Telescope at Green Bank, West Virginia

38. Radio Telescope at Green Bank, West Virginia

39. Radio Telescope at Green Bank, West Virginia

40. Arecibo Observatory (Puerto Rico)

41. Radio “image” of a Radio Galaxy, along with the visible image

42. Very Large Array Interferometer, near Socorro, New Mexico

43. Very Large Array Interferometer, near Socorro, New Mexico

44. Very Large Array Interferometer, near Socorro, New Mexico

45. ALMA = Atacama Large Millimeter Array These are somewhat more compact, and will study millimeter waves, which require a precise surface. Now installed in the Atacama desert, Chile, South America

46. The National Radio Astronomy Observatory https://public. nrao
The National Radio Astronomy Observatory has more detail on some of the newer radio telescopes This picture shows an ALMA telescope being moved up to the high desert in the Atacama desert of Chile, S. America.

47. Comparison of radio image (left) and optical image (right)

48. Infrared Telescopes are hoisted by balloons or put in orbit

49. Spitzer Infrared Telescope (Spitzer web site)

50. Infrared Image of the constellation Orion, compared to the visible image on the right

51. The Hubble Space Telescope can obtain ultraviolet pictures
The Hubble Space Telescope can obtain ultraviolet pictures. Ultraviolet images are shown using false color.

52. X-ray Telescopes are made of mirrors of special layered metal

53. Chandra Observatory, being prepared for launch

54. Chandra Observatory, mounted in the shuttle Columbia (Eileen Collins, commander) (Harvard web site) (NASA web site)

55. X-ray Image

57. Compton Gamma Ray Observatory, during deployment from the space shuttle

58. Gamma-ray Image

59. Multiple Wavelengths give us a fuller picture of the cosmos

65. The great orbiting observatories of the late 20th century: Hubble Space Telescope Spitzer Space Infrared Telescope Chandra X-ray Observatory Compton Gamma Ray Observatory XMM-Newton X-Ray Observatory (ESA) Far Ultraviolet Spectroscopic Explorer links to websites of these observatories