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Cosmology CSUDH Telescopes
This document summarizes a chapter about telescopes. It discusses how telescopes work by focusing light using lenses or mirrors. The two most important properties of telescopes are their light-collecting area and angular resolution. There are two basic designs: refracting telescopes use lenses while reflecting telescopes use mirrors. Astronomers use telescopes to take images, perform spectroscopy, and monitor light over time. Earth's atmosphere limits ground-based observations so many telescopes are placed in space. Telescopes observe different wavelengths of light by modifying their designs. Multiple telescopes can work together using interferometry to achieve very high angular resolution.
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Cosmology CSUDH Telescopes
- 1. Chapter 6 Lecture Chapter6: Telescopes Portals of Discovery © 2017 Pearson Education, Inc.
- 2. Telescopes: Portals ofDiscovery © 2017 Pearson Education, Inc.
- 3. 6.1 Eyes andCameras: Everyday Light Sensors • Our goals for learning: • How do eyes and cameras work? © 2017 Pearson Education, Inc.
- 4. The Eye © 2017Pearson Education, Inc.
- 5. Refraction • Refraction isthe bending of light when it passes from one substance into another. • Your eye uses refraction to focus light. © 2017 Pearson Education, Inc.
- 6. Example: Refraction atSunset • Sun appears distorted at sunset because of how light bends in Earth's atmosphere. © 2017 Pearson Education, Inc.
- 7. Focusing Light • Refractioncan cause parallel light rays to converge to a focus. © 2017 Pearson Education, Inc.
- 8. Image Formation • Thefocal plane is where light from different directions comes into focus. • The image behind a single (convex) lens is actually upside-down! © 2017 Pearson Education, Inc.
- 9. Recording Images • Acamera focuses light like an eye and captures the image with a detector. • The CCD detectors in digital cameras are similar to those used in modern telescopes. Digital cameras detect light with charge-coupled devices (CCDs). © 2017 Pearson Education, Inc.
- 10. Image Processing • Astronomersoften use computer software to combine, sharpen, or refine images. © 2017 Pearson Education, Inc.
- 11. What have welearned? • How do eyes and cameras work? • Eyes use refraction to bend parallel light rays so that they form an image. • The image is in focus if the focal plane is at the retina. • Cameras focus light like your eye and record the image with a detector. © 2017 Pearson Education, Inc.
- 12. 6.2 Telescopes: GiantEyes • Our goals for learning: • What are the two most important properties of a telescope? • What are the two basic designs of telescopes? • What do astronomers do with telescopes? © 2017 Pearson Education, Inc.
- 13. What are thetwo most important properties of a telescope? 1. Light-collecting area: Telescopes with a larger collecting area can gather a greater amount of light in a shorter time. 2. Angular resolution: Telescopes that are larger are capable of taking images with greater detail. © 2017 Pearson Education, Inc.
- 14. • A telescope'sdiameter tells us its light- collecting area: • The largest optical telescopes currently in use have a diameter of about 10 meters. Light-Collecting Area © 2017 Pearson Education, Inc.
- 15. Thought Question How doesthe collecting area of a 10-meter telescope compare with that of a 2-meter telescope? a) It's 5 times greater. b) It's 10 times greater. c) It's 25 times greater. © 2017 Pearson Education, Inc.
- 16. Thought Question How doesthe collecting area of a 10-meter telescope compare with that of a 2-meter telescope? a) It's 5 times greater. b) It's 10 times greater. c) It's 25 times greater. © 2017 Pearson Education, Inc.
- 17. Angular Resolution • Theminimum angular separation that the telescope can distinguish © 2017 Pearson Education, Inc.
- 18. Angular Resolution • Ultimatelimit to resolution comes from interference of light waves within a telescope. • Larger telescopes are capable of greater resolution because there's less interference. © 2017 Pearson Education, Inc.
- 19. Angular Resolution • Close-upof a star from the Hubble Space Telescope • The rings in this image of a star come from interference of light wave. • This limit on angular resolution is known as the diffraction limit. © 2017 Pearson Education, Inc.
- 20. What are thetwo basic designs of telescopes? • Refracting telescope: focuses light with lenses • Reflecting telescope: focuses light with mirrors © 2017 Pearson Education, Inc.
- 21. Refracting Telescope • Refractingtelescopes need to be very long, with large, heavy lenses. © 2017 Pearson Education, Inc.
- 22. Reflecting Telescope • Reflectingtelescopes can have much greater diameters. • Most modern telescopes are reflectors. © 2017 Pearson Education, Inc.
- 23. Designs for ReflectingTelescopes © 2017 Pearson Education, Inc.
- 24. Mirrors in ReflectingTelescopes Twin Keck telescopes on Mauna Kea in Hawaii Segmented 10-meter mirror of a Keck telescope © 2017 Pearson Education, Inc.
- 25. What do astronomersdo with telescopes? • Imaging: taking pictures of the sky • Spectroscopy: breaking light into spectra • Time Monitoring: measuring how light output varies with time © 2017 Pearson Education, Inc.
- 26. Imaging • Astronomical detectors generally recordonly one color of light at a time. • Several images must be combined to make full-color pictures. © 2017 Pearson Education, Inc.
- 27. Imaging • Astronomical detectors canrecord forms of light our eyes can't see. • Color is sometimes used to represent different energies of non-visible light. © 2017 Pearson Education, Inc.
- 28. Spectroscopy • A spectrograph separatesthe different wavelengths of light before they hit the detector. © 2017 Pearson Education, Inc.
- 29. Spectroscopy • Graphing relative brightnessof light at each wavelength shows the details in a spectrum. © 2017 Pearson Education, Inc.
- 30. Time Monitoring • Alight curve represents a series of brightness measurements made over a period of time. © 2017 Pearson Education, Inc.
- 31. Want to buyyour own telescope? • Buy binoculars first (e.g., 7×35)—you get much more for the same money. • Ignore magnification (sales pitch!). • Notice: aperture size, optical quality, portability. • Consumer research: Astronomy, Sky & Telescope, Mercury, astronomy clubs © 2017 Pearson Education, Inc.
- 32. What have welearned? • What are the two most important properties of a telescope? • Collecting area determines how much light a telescope can gather. • Angular resolution is the minimum angular separation a telescope can distinguish. • What are the two basic designs of telescopes? • Refracting telescopes focus light with lenses. • Reflecting telescopes focus light with mirrors. • The vast majority of professional telescopes are reflectors. © 2017 Pearson Education, Inc.
- 33. What have welearned? • What do astronomers do with telescopes? • Imaging • Spectroscopy • Time Monitoring © 2017 Pearson Education, Inc.
- 34. 6.3 Telescopes andthe Atmosphere • Our goals for learning: • How does Earth's atmosphere affect ground-based observations? • Why do we put telescopes into space? © 2017 Pearson Education, Inc.
- 35. How does Earth'satmosphere affect ground-based observations? • The best ground-based sites for astronomical observing are: • calm (not too windy) • high (less atmosphere to see through) • dark (far from city lights) • dry (few cloudy nights) © 2017 Pearson Education, Inc.
- 36. Light Pollution • Scatteringof human-made light in the atmosphere is a growing problem for astronomy. © 2017 Pearson Education, Inc.
- 37. Adaptive Optics • Rapidlychanging the shape of a telescope's mirror compensates for some of the effects of turbulence. Without adaptive optics With adaptive optics © 2017 Pearson Education, Inc.
- 38. Calm, High, Dark,Dry • The best observing sites are atop remote mountains. © 2017 Pearson Education, Inc. Summit of Mauna Kea, Hawaii
- 39. Why do weput telescopes into space? © 2017 Pearson Education, Inc.
- 40. Why do weput telescopes into space? A model of Hubble's successor, the James Webb Space Telescope © 2017 Pearson Education, Inc.
- 41. Transmission through Earth'sAtmosphere • Only radio and visible light pass easily through Earth's atmosphere. • We need telescopes in space to observe other forms. © 2017 Pearson Education, Inc.
- 42. What have learned? •How does Earth's atmosphere affect ground-based observations? • Telescope sites are chosen to minimize the problems of light pollution, atmospheric turbulence, and bad weather. • Why do we put telescopes into space? • Forms of light other than radio and visible do not pass through Earth's atmosphere. • Also, much sharper images are possible because there is no turbulence. © 2017 Pearson Education, Inc.
- 43. 6.4 Telescopes Acrossthe Spectrum • Our goals for learning: • How do we observe invisible light? • How can multiple telescopes work together? © 2017 Pearson Education, Inc.
- 44. How do weobserve invisible light? • A standard satellite dish is essentially a telescope for observing radio waves. © 2017 Pearson Education, Inc.
- 45. Radio Telescopes • Aradio telescope is like a giant mirror that reflects radio waves to a focus. © 2017 Pearson Education, Inc.
- 46. Infrared and UltravioletTelescopes • Infrared and ultraviolet light telescopes operate like visible-light telescopes but need to be above atmosphere to see all wavelengths. SOFIA Spitzer © 2017 Pearson Education, Inc.
- 47. X-Ray Telescopes • X-raytelescopes also need to be above the atmosphere. © 2017 Pearson Education, Inc. Chandra X-Ray Observatory
- 48. X-Ray Telescopes • Focusingof X-rays requires special mirrors. • Mirrors are arranged to focus X-ray photons through grazing bounces off the surface. © 2017 Pearson Education, Inc.
- 49. Gamma-Ray Telescopes • Gamma-raytelescopes also need to be in space. • Focusing gamma rays is extremely difficult. © 2017 Pearson Education, Inc. Fermi Gamma-Ray Observatory
- 50. Looking Beyond Light •We can also gain knowledge by collecting other signals using different sorts of "telescopes" • neutrinos • cosmic rays • gravitational waves © 2017 Pearson Education, Inc. Arial view of part of LIGO
- 51. How can multipletelescopes work together? © 2017 Pearson Education, Inc.
- 52. Interferometry • Interferometery isa technique for linking two or more telescopes so that they have the angular resolution of a single large one. © 2017 Pearson Education, Inc.
- 53. Interferometry • Easiest todo with radio telescopes • Now possible with infrared and visible-light telescopes © 2017 Pearson Education, Inc. Very Large Array (VLA)
- 54. What have learned? •How do we observe invisible light? • Telescopes for invisible light are usually modified versions of reflecting telescopes. • Many of the telescopes used for observing invisible light are in space. • How can multiple telescopes work together? • Linking multiple telescopes using interferometry enables them to produce the angular resolution of a much larger telescope. © 2017 Pearson Education, Inc.