ISP Astronomy Gary D. Westfall1Lecture 7 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 Astronomy Gary D. Westfall2Lecture 7 Types of Telescopes A telescope made with lenses is called a refracting telescope A telescope made with mirrors is called a reflecting telescope n Modern astronomical telescopes are reflecting

ISP Astronomy Gary D. Westfall3Lecture 7 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 n A = πr 2 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 n Angle subtended by a quarter at a distance of 5 km Some locations have better “seeing” n Mauna Kea, 0.3 arc-sec

ISP Astronomy Gary D. Westfall4Lecture 7 Optical Detectors and Instruments Telescopes collect and focus light Telescopes need excellent light detectors n The human eye is not a good light detector for astronomical purposes u Short integration time H Faint images need long collection times u Information recorded only in astronomer’s brain H Enough said! n Specific measurements are required u Imaging u Brightness u Spectroscopy

ISP Astronomy Gary D. Westfall5Lecture 7 Photographic and Electronic Detectors In the 20th century, photographic detection was the prime method of collecting light n Excellent spatial resolution n Poor quantum efficiency (1%) n Logarithmic response to light n Film must by analyzed by hand In recent times, electronic detectors have begun to replace film n Charge-coupled devices (CCD) n Acceptable spatial resolution n Excellent quantum efficiency (60%) n Linear response to light n Data recorded directly to computer

ISP Astronomy Gary D. Westfall6Lecture 7 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 n Infrared u Huge background from ambient heat u Detection difficult n X-rays and  -rays u Must be done outside the Earth’s atmosphere u Focusing and detection difficult n Radio waves u Require large detectors H Long wavelengths!

ISP Astronomy Gary D. Westfall7Lecture 7 Spectroscopy By analyzing the wavelength of the gathered light as well as creating an image, details of the astronomical object can be extracted n Temperature n Abundances of elements n Red shift (velocity of recession) n Information about rotation

ISP Astronomy Gary D. Westfall8Lecture 7 Picking the Best Observing Sites The performance of an optical telescopes depends on its location n Weather, clouds, fog, etc. n Humidity causes absorption of infrared n Light pollution n Stability of atmosphere Best sites are n High u Mountain tops n Dark u Isolated from civilization n Dry u Deserts n Examples u Chile, Arizona, Hawaii Kitt Peak National Observatory Tuscon, Arizona

ISP Astronomy Gary D. Westfall9Lecture 7 Major New Telescopes Kitt Peak National Observatory n Arizona, Chile European Southern Observatory n Chile Keck Observatory n Hawaii u Twin 10 m telescopes European Very Large Telescope (VLT) n Four 8 m telescopes n Chile SOAR n Southern Astrophysical Research Keck Observatory SOAR Observatory

ISP Astronomy Gary D. Westfall10Lecture 7 Information from Radio Telescopes Cosmic radio waves carry information about distant objects n In this picture, a galaxy is ejecting matter

ISP Astronomy Gary D. Westfall11Lecture 7 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 Astronomy Gary D. Westfall12Lecture 7 Observations outside the Atmosphere Infrared n On jets, balloons n Satellite, Infrared Astronomical Satellite (IRAS) Gamma rays n Compton Gamma Ray Observatory X-rays n Chandra X-ray Observatory

ISP Astronomy Gary D. Westfall13Lecture 7 Hubble Space Telescope The Hubble Space Telescope was launched April 24, 1990 by the space shuttle Discovery.

ISP Astronomy Gary D. Westfall14Lecture 7 Story of Hubble Space Telescope As told by NASA

ISP Astronomy Gary D. Westfall15Lecture 7 Movies from Hubble The HST took a series of pictures of Neptune

ISP Astronomy Gary D. Westfall16Lecture 7 HST Looking Deep The Hubble Space Telescope looks deep into the universe, as told by NASA