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Light and Telescopes Modern Astronomy Problems with ground-based observing Equipment Atmosphere Good seeing Twinkling stars Reduction in available wavelengths of light Light pollution Good Seeing Conditions Stable atmosphere Cool temperature Low humidity Long periods of stable weather Limited light pollution Where would you construct a new observatory? Mauna Kea Observatory Complex 13,796 above MSL Copyright 1998, Richard Wainscoat, All Rights Reserved Nordic Optical Telescope, La Palma, Canary Islands Photo by Bob Tubbs. Roque de los Muchachos Observatory Credit: Nik Szymanek (ING), IAC, ENO Gran Telescopia Canaries, La Palma, Canary Islands 10.4 meter multimirror reflector Palomar Mountain Observatory, San Diego County, CA Courtesy of Caltech Astronomy 200-inch primary mirror Near Atacama Desert in Chile La Silla, Chile ESO European Organisation for Astronomical Research in the Southern Hemisphere Other Notables Mount Wilson Observatory, Los Angeles, California McDonald Observatory, Texas Kitt Peak Observatory, Tuscon, AZ Yerkes Observatory, Williams Bay, WI Cincinnati Observatory Center Cincinnati Observatory Center 11” refractor (likely the oldest continuously used telescope in the world) 16” refractor (Photo courtesy COC) Photos courtesy of David Wall Angular Resolution The measure of the smallest amount of detail of an astronomical object that can be detected by a telescope. Angular size is indicated by seconds (1”) or fractions of seconds (0.01”). Unaided human eye (1’) Best without adaptive optics (0.3”) Differences in Angular Resolution http://grus.berkeley.edu/~jrg/CELT/ay250_012403.html Angular resolution of ground-based telescopes: a comparison Best resolution: 0.00001” using radio data from telescopes on opposite sides of the Earth 0.001”—VLBA across the US 0.1”—VLA radio wave observatory in New Mexico 0.3” to 0.005”—Keck Observatory, Hawaii Advanced Technology: improvements in light gathering and resolving power Previous methods long-exposure photographic plates Monster-sized primary lenses and mirrors Today Charged Coupling Devices (CCD) Active optics Adaptive optics Interferometry New technology has created chargecoupled devices (CCDs) to gather light more efficiently than photographic plates. These devices produce images with astounding detail. Shown in this picture are the intricate details of the Rosetta Nebula 5000ly away. Ordinary Photography Versus CCDs ORDINARY PHOTOGRAPH NEGATIVE NEGATIVE USING CCDs COMBINED CCD IMAGES USING COLORED FILTERS Active Optics Primary mirror receives constant adjustments to maintain best orientation. Aims the mirror (or mirrors) correctly. Adaptive Optics Computer-activated motors attached to primary mirror or other mirrors reshape the mirror to cancel out the twinkling effect caused by atmospheric turbulence. Produces even clearer images by deformation of the primary mirror. Keck Observatory—10 m “primary mirror” is actually composed of 36 hexagonal mirrors. Sixinch center mirror is diameter deformable and is adjusted up to 670 times per second. Keck Observatory, Mauna Kea, Hawaii NASA Courtesy W.H. Keck Observatory Keck 1 Primary Mirror (10 m) Credit: W. M. Keck Observatory/Gary Chanan Back of individual hexagonal reflector at Keck Observatory (Photocredit: R. Underwood.) Using adaptive optics to calculate the amount of twinkling of our atmosphere, as well as changes to the shape of the mirror, we can receive better images from ground based telescopes. IMAGES OF SATURN GROUND BASED WITH NO ADAPTIVE OPTICS GROUND BASED WITH ADAPTIVE OPTICS Interferometery Multiple telescopes interface to act as one giant telescope increases light-gathering ability and resolution produces a composite image having excellent angular resolution. Uses the physical principle of wave interference to add or subtract specific wavelengths of light. Approaches One site: very-large array (VLA), New Mexico (0.1” resolution) and Keck, Hawaii (dual telescopes 0.04” resolution) Multiple sites: very-long-baseline interferometry (VLBI) Radio telescopes separated by thousands of kilometers (0.001” resolution) NONOPTICAL ASTRONOMY Using interferometry to combine the information from two or more telescopes to create one image, radio telescopes can be linked together over large distances to overcome the limits of resolution for a single radio telescope. The radio telescope in Greenbank, West Virginia, has an off-center secondary which does not block incoming radio waves. The Very Large Array (VLA) in central New Mexico combines the signals from 27 radio telescopes to either cover wide areas of the sky or increase the resolution for a small area. Beyond the Hindrance of the Earth’s Atmosphere Sky & Telescope illustration by Kevin Sartoris. Ground Based Telescopes are Limited Our atmosphere causes the stars to appear to shift in color and brightness. This causes the star to appear to flicker. We call this twinkling. GROUND BASED TELESCOPES BLURRED BY TWINKLING TELESCOPES IN ORBIT ABOVE OUR ATMOSPHERE AVOID THIS PROBLEM Light from cities scatters in our atmosphere reducing the visibility of celestial objects. This is called light pollution, and has been an increasing problem in recent years. The view from Kitt Peak National Observatory of the Tuscon, Arizona skyline in 1959 The same skyline in 1972 The transparency of a material depends on the wavelength of light. Earth’s atmosphere is relatively transparent to visible light and radio waves, which are referred to as “windows” through which we can view space from a ground-based telescope. Not every wavelength of light passes through the Earth’s Atmosphere! To avoid adverse effects of our atmosphere, we launch telescopes on satellites that circle the Earth above the atmosphere. THE HUBBLE SPACE TELESCOPE (HST) Using adaptive optics to calculate the amount of twinkling of our atmosphere, as well as changes to the shape of the mirror, we can receive better images from ground based telescopes. IMAGES OF SATURN GROUND BASED WITH NO ADAPTIVE OPTICS GROUND BASED WITH ADAPTIVE OPTICS HUBBLE IMAGE Images of Saturn IN VISIBLE LIGHT IN RADIO WAVES NOTE: We use falsecolor images when displaying data from non-visible light. Radio Wave Telescope, Arecibo, Puerto Rico The Spitzer Space Telescope will examine infrared cosmos Mirror Setup Launched in 2003 Non Optical Images of the Sun Reveal Details which Cannot be Observed in Visible Light X-RAY X-ray image VISIBLE Kitt Peak National Observatory Different Views of Our Universe We are familiar with the view of our surrounding universe in visible light Astronomers also study our universe using other wavelengths of light to unlock its secrets RADIO WAVES INFRARED X-RAYS GAMMA RAYS A space-based telescope for every purpose…and for every wavelength! Radio waves (see ground-based telescopes) Microwaves Infrared light Far Ultraviolet Spectroscopic Explorer (FUSE), Extreme Ultraviolet Explorer (EUVE), Galaxy Evolution Explorer (GALEX) X-rays Hubble Space Telescope (HST) Ultraviolet light Infrared Astronomical Satellite (IRAS), Infrared Space Observatory (ISO), Spitzer Space Telescope (SST) Visible light Wilkinson Microwave Anisotropy Probe (WMAP) Chandra X-ray Observatory (CXO), Multi-Mirror Telescope (XMM-Newton) Gamma Rays Swift gamma ray bursts detector Telescopes for Observing the Sun Monitoring Aspects of the Sun Solar and Heliospheric Observatory (SOHO) http://sohowww.nascom.nasa.gov/ Rauven Ramaty High Energy Solar Spectroscopic Imager (RHESSI) Hard X-ray Spectrometer (HXRS) Monitoring Space Weather Advanced Composition Explorer (ACE) Geostationary Operational Environmental Satellite (GOES) Solar X-ray Imager (SXI) Who’s Involved in Space Exploration? National Aeronautics and Space Administration (NASA) http://www.nasajobs.nasa.gov/work/where.htm European Space Agency (ESA) German Space Agency (DSL) Russian Space Agency (ROSCOSMOS) Japanese Space Agency Chinese Space Agency And so on… WHAT DID YOU THINK? What is light? One form of electromagnetic radiation with both wave and particle properties. Which type of electromagnetic radiation is most dangerous to life? Gamma rays. What is the main purpose of a telescope? To collect as much light as possible. Why do stars twinkle? Rapid changes in the density of the Earth’s atmosphere cause passing light starlight to change direction. What type(s) of electromagnetic radiation can telescopes currently detect? Some can detect the entire electromagnetic spectrum. Key Terms active optics adaptive optics angular resolution (resolution) blocked light blueshift Cassegrain focus charge-coupled device (CCD) coude focus Doppler shift electromagnetic radiation electromagnetic spectrum eyepiece lens focal length focal plane focal point gamma ray infrared radiation interferometry light-gathering power magnification Newtonian reflector objective lens photon pixel primary mirror prime focus radio telescope radio wave redshift reflecting telescope reflection refracting telescope refraction Schmidt corrector plate secondary mirror seeing disk spectrum spherical aberration twinkling ultraviolet (UV) radiation very-long-baseline interferometry (VLBI) wavelength X ray