Tools of the Trade

1. Tools of the Trade Astronomy 112 Stars & Galaxies Chapter 5

2. Telescopes • Gather light for analysis • Different telescopes for different wavelengths • Bigger telescopes gather more light • Specialized detectors for atomic particles

3. Telescopes • Two main types • Reflectors – use mirrors • Refractors – use lenses

4. What can we see? • Resolution • Seeing

5. Resolution • Smallest details we can see • The angle between objects that can barely be distinguished • Diffraction sets the best possible resolution • Bending of light around telescope optics

6. Diffraction Limit • Limit of resolution • Expressed as angle in arcseconds • For D=3 m, θ=0.04 arcsec • For particular diameter, resolution is better at shorter wavelengths • At a particular wavelength, resolution is better for larger telescope

7. Diffraction Limit

8. Seeing • Atmospheric effect • Blurring degrades resolution • Seeing = size of image produced • Typically, seeing is ½ to 1 arcsec • Space-based telescopes don’t have this problem • Some ground-based telescopes minimize effects with adaptive optics

9. Seeing • Atmospheric effect • Blurring degrades resolution • Seeing = size of image produced • Typically, seeing is ½ to 1 arcsec • Space-based telescopes don’t have this problem • Some ground-based telescopes minimize effects with adaptive optics

10. Reflectors vs Refractors • Refractors • Aberration – notably chromatic

11. Reflectors vs Refractors • Refractors • Aberration – notably chromatic • Difficult & expensive to produce • Surfaces are expensive/difficult to shape • Lenses can only be supported on edges

12. Reflectors vs Refractors • Refractors • All modern astronomical telescopes • Less aberration • Less light loss • Easier to build

13. Reflectors vs Refractors • Refractors • Many types • Newtonian focus • Spherical or paraboloidal mirror • Simple & cheap • Cassegrain focus • Parabolic primary • hyperbolic secondary

14. Reflectors vs Refractors • Refractors • Many types • Schmidt-Cassegrain • Corrector plate corrects spherical aberration • Short, squat tubes • Classic wide-field tubes • Maksutov-Cassegrain

15. Reflectors vs Refractors • Refractors • Many types • Ritchey-Chrétien • specialized Cassegrain • two hyperbolic mirrors • free of coma & spherical aberration at focal plane • suitable for wide field & photographic applications

16. Reflectors vs Refractors • Refractors

17. Reflectors vs Refractors • Refractors Applause

18. Observatories • Mountain-top observatories • Less atmosphere • Less turbulence • Less humidity • Mauna Kea (Hawaii)

19. Observatories • Mountain-top observatories • Kitt Peak • SW of Tucson

20. Observatories • Mayall 4-m telescope • Kitt Peak • Cassegrain focus

21. Observatories • Mayall 4-m telescope • Kitt Peak • Cassegrain focus

22. Observatories • Mayall 4-m telescope • Kitt Peak • Cassegrain focus

23. Observatories • Observatorio del Roque de los Muchachos • Canary Islands

25. Observatories • Observatorio del Roque de los Muchachos • Canary Islands

26. Observatories • Grand Telescopio Canarias • Observatorio del Roque de los Muchacho • 10.4 m

27. Observatories • Grand Telescopio Canarias

28. Observatories • William Herschel Telescope (WHT) • 4.2 m • Theoretical maximum resolution < 0.2″ • Typical seeing at La Palma ~1″

29. Observatories • MAGIC telescope • Major Atmospheric Gamma-ray Imaging Cherenkov Telescope • 17-m reflecting surface

30. Observatories • Keck Telescope • 10 m • Mauna Kea, Hawaii

31. Observatories • Keck Telescope • 10 m

32. Optical Windows • Atmosphere is not transparent at all wavelengths • Many important wavelengths don’t reach ground • UV, X-rays • Satellites are used for these

33. Capturing the Light • Astronomers don’t look through telescopes • Electronic devices record light • CCDs – charge-coupled devices (digital cameras) • Two modes: • Direct imaging (pictures) • Spectroscopy (separate wavelengths)

34. Radio Telescopes • Observations with λ > 10 cm. • Telescopes can be very large, but still have low resolution because of large λ. • Can increase resolution by combining many telescopes into an interferometric array. • Resolution is like that of a telescope many km across.

36. Radio Telescopes • Radio astronomy reveals several features • Neutral hydrogen clouds • ~90 % of all the atoms in the Universe • Molecules • often located in dense clouds, where visible light is completely absorbed • Radio waves penetrate gas and dust clouds • observe regions from which visible light is heavily absorbed

37. Other detectors • In a few cases, we capture things other than electromagnetic radiation: • Neutrinos – light subatomic particles • Elementary particles – protons & electrons • In the Solar Wind • Gravity waves – distortions in spacetime predicted by gravity

38. Avoiding the Atmosphere Air Bad!!!

39. Avoiding the Atmosphere

40. Avoiding the Atmosphere • Balloons and aircraft: • raise the telescope above clouds and water vapor (infrared astronomy). • Satellites: • Detect wavelengths that the atmosphere blocks • UV to X-rays • Can produce very sharp images • e.g., the Hubble Space Telescope

41. Hubble Space Telescope • launched in 1990; maintained & upgraded by Space Shuttle missions • avoids atmospheric distortions • extends imaging and spectroscopy to IR and UV • Operational until at least 2014 • successor JWST is strictly IR-telescope

42. Hubble Space Telescope (HST)

43. Hubble Space Telescope

44. Hubble Space Telescope

45. Hubble Space Telescope

46. Hubble Space Telescope

47. Hubble Space Telescope

48. Hubble Space Telescope Applause

49. Beyond Hubble • James Webb Space Telescope

50. Special Instruments • Imaging • Photographic plates • Charge-Coupled Device (CCD) • more sensitive • computer memory • storage & manipulation