1. Chapter 6: Telescopes – Portals of Discovery

2. Visible light is only one type of electromagnetic radiation emitted by stars Each type of EM radiation travels at exactly the same speed - the speed of light!

3. Not all EM radiation can penetrate Earths atmosphere.

4. Different types of EM radiation require different types of telescopes A refracting telescope uses a lens to concentrate incoming light A refracting telescope uses a lens to concentrate incoming light A reflecting telescope uses mirrors to concentrate incoming starlight A reflecting telescope uses mirrors to concentrate incoming starlight

5. © 2014 Pearson Education, Inc. Refracting Telescope Refracting telescopes need to be very long, with large, heavy lenses. Refracting telescopes need to be very long, with large, heavy lenses.

6. A refracting telescope uses a lens to concentrate incoming light Similar to a magnifying glass

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

9. lenses reverse images

10. Three main functions of a telescope brighten brighten (called light collecting area) see fine detail see fine detail (called angular resolution) and least important, magnify magnify magnification = (objective lens focal length / eyepiece lens focal length)

11. Refracting telescopes have drawbacks Spherical aberration Spherical aberration Chromatic aberration Chromatic aberration

12. Special achromatic compound lenses and lens coatings can often fix this aberration

13. Refracting telescopes have drawbacks Spherical aberration Spherical aberration Chromatic aberration Chromatic aberration Sagging due to gravity distorting the lens Sagging due to gravity distorting the lens Unwanted refractions Unwanted refractions opaque to certain wavelengths of light opaque to certain wavelengths of light

14. © 2014 Pearson Education, Inc. Reflecting Telescope Reflecting telescopes can have much greater diameters. Reflecting telescopes can have much greater diameters. Most modern telescopes are reflectors. Most modern telescopes are reflectors.

15. © 2014 Pearson Education, Inc. Designs for Reflecting Telescopes

17. © 2014 Pearson Education, Inc. Twin Keck telescopes on Mauna Kea in Hawaii Segmented 10-meter mirror of a Keck telescope Pick-up images. Mirrors in Reflecting Telescopes

18. Astronomers face two major obstacles in observing the stars Light Pollution from Cities Light Pollution from Cities Effects of Twinkling from Earths atmosphere Effects of Twinkling from Earths atmosphere

19. Light Pollution Scattering of human-made light in the atmosphere is a growing problem for astronomy. Scattering of human-made light in the atmosphere is a growing problem for astronomy.

20. Tucson, Arizona in 1959 and 1980

21. © 2014 Pearson Education, Inc. Bright star viewed with ground- based telescope Same star viewed with Hubble Space Telescope Twinkling and Turbulence Turbulent air flow in Earth's atmosphere distorts our view, causing stars to appear to twinkle.

22. Rapid changes in the density of Earths atmosphere cause passing starlight to quickly change direction, making stars appear to twinkle.

23. Advanced technology is spawning a new generation of equipment to view the universe CCDs (charge-coupled devices) CCDs (charge-coupled devices) Large telescopes on remote mountain tops Large telescopes on remote mountain tops –Mauna Kea in Hawaii –Cerro Pachon in Chile Adaptive Optics to counteract the blurring of Earths atmosphere Adaptive Optics to counteract the blurring of Earths atmosphere Orbiting space observatories Orbiting space observatories

24. A Charge-Coupled Device (CCD)

25. Ordinary Photographs vs. CCDs

26. Matching 10-m, multiple mirror Keck Telescopes in Hawaii with adaptive optics

27. © 2014 Pearson Education, Inc. Without adaptive opticsWith adaptive optics Adaptive Optics Rapidly changing the shape of a telescope's mirror compensates for some of the effects of turbulence.

28. © 2014 Pearson Education, Inc. Summit of Mauna Kea, Hawaii Calm, High, Dark, Dry The best observing sites are atop remote mountains.

29. High above Earths atmosphere, the Hubble Space Telescope provides stunning details about the universe

30. Observations at wavelengths other than visible light are revealing previously invisible sights Visible light imageradio wavelength image

31. Radio wavelength observations are possible from Earths surface

32. © 2014 Pearson Education, Inc. Radio Telescopes A radio telescope is like a giant mirror that reflects radio waves to a focus.

33. © 2014 Pearson Education, Inc. SOFIASpitzer Infrared and Ultraviolet Telescopes Infrared and ultraviolet light telescopes operate like visible- light telescopes but need to be above atmosphere to see all wavelengths.

34. © 2014 Pearson Education, Inc. X-Ray Telescopes Focusing of X-rays requires special mirrors. Mirrors are arranged to focus X-ray photons through grazing bounces off the surface.

35. © 2014 Pearson Education, Inc. Fermi Gamma-Ray Observatory Gamma-Ray Telescopes Gamma-ray telescopes also need to be in space. Focusing gamma rays is extremely difficult.

36. © 2014 Pearson Education, Inc. Interferometry Interferometery is a technique for linking two or more telescopes so that they have the angular resolution of a single large one.

37. The Very Large Array (VLA) in New Mexico

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

39. The Future of Telescopes? Telescopes at Lagrange Points Telescopes at Lagrange Points Telescopes on other planets/moons Telescopes on other planets/moons A large telescope to take over for Hubble on the Moons polar region A large telescope to take over for Hubble on the Moons polar region Better telescopes on Earth, larger, coupled Better telescopes on Earth, larger, coupled Gravity wave detectors Gravity wave detectors Improved optics….. Improved optics…..