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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 ISP 205 - Astronomy Gary D. Westfall Lecture 7 1 Types of Telescopes • A telescope made with lenses is called a refracting telescope Objective Eyepiece • A telescope made with mirrors is called a reflecting telescope Modern astronomical telescopes are reflecting ISP 205 - Astronomy Gary D. Westfall Lecture 7 2 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 ISP 205 - Astronomy Gary D. Westfall Lecture 7 3 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 Information recorded only in astronomer’s brain Faint images need long collection times Enough said! Specific measurements are required Imaging Brightness Spectroscopy ISP 205 - Astronomy Gary D. Westfall Lecture 7 4 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 ISP 205 - Astronomy Gary D. Westfall Lecture 7 5 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! ISP 205 - Astronomy Gary D. Westfall Lecture 7 6 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 ISP 205 - Astronomy Gary D. Westfall Lecture 7 7 Picking the Best Observing Sites • 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 Dark Isolated from civilization Dry Mountain tops Deserts Examples Chile, Arizona, Hawaii ISP 205 - Astronomy Gary D. Westfall Kitt Peak National Observatory Tuscon, Arizona Lecture 7 8 Major New Telescopes • Kitt Peak National Observatory Arizona, Chile • European Southern Observatory Chile • Keck Observatory Keck Observatory Hawaii Twin 10 m telescopes • European Very Large Telescope (VLT) Four 8 m telescopes Chile SOAR Observatory • SOAR Southern Astrophysical Research ISP 205 - Astronomy Gary D. Westfall Lecture 7 9 Information from Radio Telescopes • Cosmic radio waves carry information about distant objects In this picture, a galaxy is ejecting matter ISP 205 - Astronomy Gary D. Westfall Lecture 7 10 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 ISP 205 - Astronomy Gary D. Westfall Lecture 7 11 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 ISP 205 - Astronomy Gary D. Westfall Lecture 7 12 Hubble Space Telescope • The Hubble Space Telescope was launched April 24, 1990 by the space shuttle Discovery. ISP 205 - Astronomy Gary D. Westfall Lecture 7 13 Story of Hubble Space Telescope • As told by NASA QuickTime™ and a Sorenson Video decompressor are needed to see this picture. ISP 205 - Astronomy Gary D. Westfall Lecture 7 14 Movies from Hubble • The HST took a series of pictures of Neptune QuickTime™ and a decompressor are needed to see this picture. ISP 205 - Astronomy Gary D. Westfall Lecture 7 15 HST Looking Deep • The Hubble Space Telescope looks deep into the universe, as told by NASA QuickTime™ and a Sorenson Video decompressor are needed to see this picture. ISP 205 - Astronomy Gary D. Westfall Lecture 7 16