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Telescopes

Telescopes. Galileo first used a telescope to observe the sky in 1610 The main function of a telescope is to gather faint light from an astronomical source and to focus that light into an image The light gathering ability of a telescope is defined by its diameter or aperture

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Telescopes

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  1. Telescopes • Galileo first used a telescope to observe the sky in 1610 • The main function of a telescope is to gather faint light from an astronomical source and to focus that light into an image • The light gathering ability of a telescope is defined by its diameter or aperture • Before the 20th century, astronomer looked through the telescope with their eyes • Today the images are recorded photographically and electronically Lecture 7

  2. Types of Telescopes • A telescope made with lenses is called a refracting telescope • A telescope made with mirrors is called a reflecting telescope • Modern astronomical telescopes are reflecting Lecture 7

  3. Properties of Images • The brightness of an image is determined by the area of the collector • The brightness of an image is proportional to the aperture squared • A = πr2 • The main use of large aperture telescopes is to gather as much light as possible from faint sources • Resolution refers to the fineness of details in an image • Atmospheric instability limits most ground based telescopes to a resolution of 1 arc-sec • Angle subtended by a quarter at a distance of 5 km • Some locations have better “seeing” • Mauna Kea, 0.3 arc-sec Lecture 7

  4. Optical Detectors and Instruments • Telescopes collect and focus light • Telescopes need excellent light detectors • The human eye is not a good light detector for astronomical purposes • Short integration time • Faint images need long collection times • Information recorded only in astronomer’s brain • Enough said! • Specific measurements are required • Imaging • Brightness • Spectroscopy Lecture 7

  5. Photographic and Electronic Detectors • In the 20th century, photographic detection was the prime method of collecting light • Excellent spatial resolution • Poor quantum efficiency (1%) • Logarithmic response to light • Film must by analyzed by hand • In recent times, electronic detectors have begun to replace film • Charge-coupled devices (CCD) • Acceptable spatial resolution • Excellent quantum efficiency (60%) • Linear response to light • Data recorded directly to computer Lecture 7

  6. Observing with Nonvisible EM Radiation • Astronomers also observe the sky with different wavelength EM radiation • Different wavelengths carry a wealth of information have their challenges • Infrared • Huge background from ambient heat • Detection difficult • X-rays and -rays • Must be done outside the Earth’s atmosphere • Focusing and detection difficult • Radio waves • Require large detectors • Long wavelengths! Lecture 7

  7. Spectroscopy • By analyzing the wavelength of the gathered light as well as creating an image, details of the astronomical object can be extracted • Temperature • Abundances of elements • Red shift (velocity of recession) • Information about rotation Lecture 7

  8. Picking the Best Observing Sites Kitt Peak National Observatory Tuscon, Arizona • The performance of an optical telescopes depends on its location • Weather, clouds, fog, etc. • Humidity causes absorption of infrared • Light pollution • Stability of atmosphere • Best sites are • High • Mountain tops • Dark • Isolated from civilization • Dry • Deserts • Examples • Chile, Arizona, Hawaii Lecture 7

  9. Major New Telescopes Keck Observatory SOAR Observatory • Kitt Peak National Observatory • Arizona, Chile • European Southern Observatory • Chile • Keck Observatory • Hawaii • Twin 10 m telescopes • European Very Large Telescope (VLT) • Four 8 m telescopes • Chile • SOAR • Southern Astrophysical Research Lecture 7

  10. Information from Radio Telescopes • Cosmic radio waves carry information about distant objects • In this picture, a galaxy is ejecting matter Lecture 7

  11. Radio Telescopes • Radio telescopes need to be large because of the long wavelength of radio waves and to collect as much signal as possible • Radio waves are reflected by electrically conducting surfaces and the signal is collected by sensitive radio receivers Lecture 7

  12. Observations outside the Atmosphere • Infrared • On jets, balloons • Satellite, Infrared Astronomical Satellite (IRAS) • Gamma rays • Compton Gamma Ray Observatory • X-rays • Chandra X-ray Observatory Lecture 7

  13. Hubble Space Telescope • The Hubble Space Telescope was launched April 24, 1990 by the space shuttle Discovery. Lecture 7

  14. Story of Hubble Space Telescope • As told by NASA Lecture 7

  15. Movies from Hubble • The HST took a series of pictures of Neptune Lecture 7

  16. HST Looking Deep • The Hubble Space Telescope looks deep into the universe, as told by NASA Lecture 7

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