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Announcements. Turn in Homework 5, pick up Homework 6. Another test this week! Same days (W,Th), same format as before. First project due October 13. Telescopes. 2 October 2006. Today:. Different telescope designs Why bigger is better Research telescopes, past and present

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Announcements

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  1. Announcements • Turn in Homework 5, pick up Homework 6. • Another test this week! Same days (W,Th), same format as before. • First project due October 13.

  2. Telescopes 2 October 2006

  3. Today: • Different telescope designs • Why bigger is better • Research telescopes, past and present • Light detectors • Telescopes for invisible “light” and other signals • Amateur telescopes

  4. Purpose of a telescope: Gather light over a large areaand focus it onto a small area Method 1: Refraction (using a convex lens) Disadvantages: Hard to make a large lens with two perfect surfaces; hard to support a large lens by edges; different colors are focused at slightly different distances

  5. Purpose of a telescope: Gather light over a large areaand focus it onto a small area Method 2: Reflection (using a concave mirror) Disadvantage: Focal point is within the incoming light path.

  6. Largest refractor and reflector 10-meter reflector (Keck telescope), Mauna Kea, Hawaii 1-meter refractor, Yerkes Observatory, Wisconsin

  7. Light-gathering ability 1 meter across 10 meters across A 10-meter telescope gathers 100 times as much light as a 1-meter telescope.

  8. Resolving Power(Ability to see detail) Wave behavior of light causes diffraction: bending at the edges of the telescope. The wider the telescope’s lens or mirror, the less diffraction and the more detail can be resolved. Light with a shorter wavelength also diffracts less. But: Air turbulence usually causes even more blurring.

  9. Reflector Designs Diffraction spikes from secondary mirror supports

  10. Early Telescopes Newton’s reflector Galileo’s refractor

  11. The first big reflectors William Herschel’s largest telescope (late 1700’s) Lord Rosse’s telescope (1840’s)

  12. Large Photographic Telescopes 2.5 meter Hooker telescope, Mt. Wilson, California

  13. Large Photographic Telescopes Prime focus 5 meter Hale telescope, Mt. Palomar, California

  14. Book Recommendation: First Light, by Richard Preston. Describes the “Big Eye” and the other telescopes at Palomar Observatory, as well as the research done there and some of the more interesting researchers.

  15. Light Detectors • Human eye • Photographic emulsions (late 1800’s) • Electronic cameras (1970’s) • Spectrographs (prisms or diffraction gratings) combined with one of the above

  16. Other Wavelengths

  17. Radio Telescopes

  18. HiRes Fly’s Eye Cosmic Ray Detector(Utah west desert)

  19. Hubble Space Telescope

  20. Other space telescopes X-ray Infrared

  21. Advantages of space telescopes • Observe wavelengths that don’t penetrate earth’s atmosphere • Sharper images without atmospheric refraction (“twinkling”) Mars from earth’s surface Mars from Hubble • NASA has lots of money

  22. Other signals (besides “light”) • Cosmic rays (charged subatomic particles that collide with earth’s atmosphere) • Neutrinos (highly penetrating particles, given off by sun and other stars) • Gravitational waves (not yet detected directly)

  23. Neutrino Detectors

  24. Gravitational Wave Detectors (LIGO) Hanford, WA Livingston, LA Proposed “LISA” detector in solar orbit

  25. Telescopes for amateur use • Binoculars • Small refractors • Dobsonian reflectors • Motor-driven telescopes

  26. Binoculars Great for viewing the moon, Jupiter’s moons, Milky Way, and several of the brighter star clusters, nebulae, and galaxies. Mostly for daytime use 7 x 50 (my favorite) Too big to hold steady

  27. Small Refractors OK for viewing moon and planets, IF the mount is steady. Usually a major disappointment. Beware of cheap department store brands! High-magnification eyepieces are useless.

  28. Dobsonian Reflectors These are Newtonian reflectors with a simple mounting system designed by John Dobson. Versatile, economical, and very easy to use! Sizes range from 4.5 inches to 25 inches and more.

  29. Motor-Driven Telescopes For the serious amateur astronomer/astrophotographer. Rather expensive compared to Dobsonians.

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