Light (Electromagnetic Spectrum) and Telescopes [week 2 and 3]

1. Light (Electromagnetic Spectrum) andTelescopes[week 2 and 3]

2. A Telescope is a tool used to gather light from objects in the universe

3. Our Objective OBJECTIVES • Treat the telescopes as an instrument • Learn telescope parameters • What makes a telescope useful? • Telescope operation • Different telescope types

4. There are two different types of telescopes • A refracting telescope uses a glass lens to concentrate incoming light • A reflecting telescope uses mirrors to concentrate incoming starlight

5. Telescope Optics

6. Objective (lens) eyepiece 40” Refractor 2.4” Amateur Refractor The Refractor • Common as small telescopes • $$$ in large apertures • Superb image quality

7. 6” Amateur Newtonian • Common as amateur telescopes • Lower cost • Simple optical design • Good image quality • Central obstruction The Newtonian Reflector

8. The Cassegrain Reflector • Large f-number in small package • F/10 in a 24” long tube • Good imagery for large f/# • Design used in large telescopes

9. Spherical primary mirror Corrector plate The Schmidt Cassegrain 8” Schmidt Cassegrain • Large f-number in small package • F/10 in a 24” long tube • Good imagery for large f/# • Better spherical aberration control

10. Chromatic AberrationThe Problem

11. Chromatic AberrationThe Solution

12. Spherical Aberration

13. Spherical Aberration

14. A ____________ telescope uses a lens to concentrate incoming light

15. Reflecting telescopes use mirrors to concentrate incoming starlight

16. Three main functions (Powers) of a Telescope Most important!! • Light Gathering Power: bigger aperture is better making objects appear brighter followed by • Resolving Power:to see fine detail and least important, • Magnifying Power: magnification = M

17. SENSITIVITY HOW MUCH LIGHT CAN THE TELESCOPE GATHER DEPENDS ON THE -APERTURE- SIZE OF THE MIRROR OR LENS

18. eye Eye behind telescope Light Gathering Power“The Power of a Telescope”

19. Telescope Resolving Power Star Double Star

20. DIFFRACTION

22. RESOLUTION AND THE AIRY DISC

23. RESOLUTION  = 4.56 / D • is the separation in arc seconds D is the diameter of lens/mirror in inches

24. A larger objective lens provides a brighter (not bigger) image

25. 2000 mm ÷ 76 mm = 78 X 2000 mm ÷ 10 mm = 200 X 2000 mm ÷ 1 mm = 2000X Magnification Magnification = Telescope focal length ÷ eyepiece focal length Maximum useful magnification: - 60X per 1” of aperture Practical magnification depends on - Optics and seeing

26. See faint objects - Light gathering power See detail on objects - Resolving power Magnify otherwise small objects - Magnification The Job of a Telescope

27. Reflecting telescopes use mirrors to concentrate incoming starlight

28. Advantages and Disadvantages of Various Telescopes See One-Minute Astronomer worksheet and notes below previous slide.

29. If you pass white light through a prism, it separates into its component colors. long wavelengths ROY G B I V short wavelengths spectrum

30. But visible light is only one type of electromagnetic radiation (light) emitted by stars Astronomers are truly interested in the entire spectrum of Light!

32. Consider This Class as Seen in Different Wavelengths of Light!

33. Consider Orion as Seen in Different Wavelengths of Light!

34. Observations at other wavelengths are revealing previously invisible sights UV infrared Map of Orion region Ordinary visible

35. Hubble Space Telescope Views of Orion Nebula showing stars hidden in clouds http://oposite.stsci.edu/pubinfo/pr/97/13/A.html

36. TODAY’S Sun as seen in visible light from Earth and from space in X-rays by satellites

37. Radio wavelength observations are possible from Earth’s surface

38. The Very Large Array (VLA) in New Mexico One such array is called the Very Large Baseline Array (VLBA): it consists of ten radio telescopes which reach all the way from Hawaii to Puerto Rico: nearly a third of the way around the world! By putting a radio telescope in orbitaround the Earth, radio astronomers could make images as if they had a radio telescope the size of the entire planet!

41. Why do some stars, sky objects appear to twinkle? Differences in the temperature and density of small portions of Earth’s atmosphere cause passing starlight to quickly change direction, making stars appear to twinkle.

42. Image of stars taken with a telescope on the Earth’s surface Same picture taken with Hubble Space Telescope high above Earth’s blurring atmosphere Earth’s atmosphere hinders astronomical research

43. High above Earth’s atmosphere, the Hubble Space Telescope provides stunning details about the universe

44. Hubble orbits the Earth at an altitude of about 353 miles and in 97 minutes.

45. But visible light is only one type of electromagnetic radiation (light) emitted by stars Astronomers are truly interested in the entire spectrum of Light!

46. Astronomers use different instruments to look at light of different wavelengths - sometimes, we even have to go above Earth’s atmosphere.

47. Not all EM radiation can penetrate Earth’s atmosphere.

48. Which is the correct reasoning for why a gamma ray telescope located in Antarctica that is to be used to look for evidence of black holes in the centers of galaxies would not get funded? • There is no way to detect the presence of a black hole. • Gamma rays are too energetic to detect with a telescope. • You can’t build a functioning telescope in Antarctica. • Gamma rays don’t penetrate Earth’s atmosphere.

49. Imagine you’re the head of a funding agency that has a very tight budget for building a telescope. Which of the three proposed telescopes below would be best to support? • A gamma ray telescope in Antarctica • A radio telescope in orbit above the Earth • A visible telescope located high on a mountain in Peru • An ultraviolet telescope located in the Mojave desert