Transcript Chapter 1
Chapter 5 Astronomical Instruments How do we learn about objects too far away for spacecraft? How do telescopes work? Do all telescopes use light? Why are telescopes located on mountains? Why are some telescopes in orbit around the Earth? January 24, 2006 Astronomy 2010 1 5.1 Telescopes • Telescopes are devices for “seeing” distant objects. – To see faint objects, collect more light by using a bigger aperture. – Magnification is much, much less important. • Two types of optical telescopes: – Refracting – Reflecting January 24, 2006 Astronomy 2010 2 Refracting Telescopes • Use a large lens as the primary light collecting element. • Common in older telescopes. • Chromatic aberrations and ultraviolet cutoff. January 24, 2006 Astronomy 2010 3 January 24, 2006 Astronomy 2010 4 Reflecting Telescopes • Use a large mirror as the primary light collecting element. • Easier to make a large mirror than a large lens. • Modern telescopes are reflectors. • Reduced chromaticity problems. January 24, 2006 Astronomy 2010 5 Refracting versus Reflecting January 24, 2006 Astronomy 2010 6 Prime, Newton, and Cassegrain January 24, 2006 Astronomy 2010 7 5.2 Optical Detectors and Instruments • Second greatest advance in astronomy was the use of photographic film – Longer integration time than the eye. – Images available for later (re)inspection. • The 3 uses of telescopes: – Imaging – Measuring brightness and color – Spectroscopy • All benefit from longer integration time. January 24, 2006 Astronomy 2010 8 Charge-Coupled Device • A modern advance is the use of chargecoupled devices or CCD’s. • These are the “digital film” of digital cameras. January 24, 2006 Astronomy 2010 9 5.3 Optical and Infrared Observatories • Ground based telescopes are housed in domes or other structures to protect them when not in use. • They are often located on remote mountains, away from lights, and smog, and above humid and turbulent air. January 24, 2006 Astronomy 2010 10 NOAO on Kitt Peak, AZ January 24, 2006 Astronomy 2010 11 South African Large Telescope January 24, 2006 Astronomy 2010 12 European Southern Observatory January 24, 2006 Astronomy 2010 13 Choice of Telescope Sites • Weather: clouds, wind, and rain limit observing time. • Water vapor: water vapor in the atmosphere filters out infrared wavelengths. • Darkness: city light can overwhelm faint stars. • Turbulence: turbulent air blurs images. January 24, 2006 Astronomy 2010 14 Observatory Sites • Newest telescopes are sited in the Chilean Andes, desert peaks of Arizona, Canary Islands, and Mauna Kea in Hawaii. • Modern telescopes can use segmented mirrors, adaptive optics, and interferometry. January 24, 2006 Astronomy 2010 15 Observing Other Radiation • To learn the most about planets, stars, and galaxies, astronomers use as many types of radiations as possible. – – – – Radio Infrared and ultraviolet X-rays Gamma rays January 24, 2006 Astronomy 2010 16 5.4 Radio Telescopes • Many objects emit radio waves, from long wave to microwaves. • Radio telescopes generally look like large satellite dishes. • They can operate during the day and night. • Large facilities in Puerto Rico, West Virginia, and New Mexico. January 24, 2006 Astronomy 2010 17 January 24, 2006 Astronomy 2010 18 The Very Large Array (VLA) January 24, 2006 Astronomy 2010 19 The VLBA Spans A Continent January 24, 2006 Astronomy 2010 20 Radio Image of Quasar Jets January 24, 2006 Astronomy 2010 21 5.5 Observatories Outside the Earth’s Atmosphere • Some wavelengths of radiation are absorbed by Earth’s atmosphere (gamma rays, x-rays, and ultraviolet). • Telescopes for these wavelengths must be put in space. • The Hubble telescope demonstrates the advantages for an optical telescope to be above the atmosphere. January 24, 2006 Astronomy 2010 22 The Hubble Space Telescope January 24, 2006 Astronomy 2010 23 The Swift Satellite (GRB’s) January 24, 2006 Astronomy 2010 24