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Unformatted text preview: Tools of Astronomy A refracting telescope uses a lens to concentrate incoming light
Similar to a magnifying glass brighten (called light gathering power) see fine detail (called resolution) and least important, magnify Three main functions of a telescope magnification = (objective lens focal length / eyepiece lens focal length) Astronomical tools Optical (visible light) telescopes Two basic types Refracting telescope Reflecting telescope Optical (visible light) telescopes Two basic types Astronomical tools Refracting telescope Uses a lens (called the objective) to bend (refract) the light to produce an image Light converges at an area called the focus Distance between the lens and the focus is called the focal length The eyepiece is a second lens used to examine the image directly Have an optical defect called chromatic aberration (color distortion) Refracting telescopes have drawbacks
Spherical aberration Chromatic aberration If you pass white light through a prism, it separates into its component colors. long wavelengths R.O.Y. G. B.I.V short wavelengths spectrum Special achromatic compound lenses and lens coatings can often fix this aberration Refracting telescopes have drawbacks Spherical aberration
Chromatic aberration Sagging due to gravity distorting the lens Unwanted refractions opaque to certain wavelengths of light lenses reverse images A simple refracting telescope Astronomical tools Optical (visible light) telescopes Two basic types Reflecting telescope Uses a concave mirror to gather the light No color distortion Nearly all large telescopes are of this type Newtonian Focus Cassegrain focus Prime Focus coude' focus A prime focus reflecting telescope Cassegrain focus reflecting telescope Newtonian focus reflecting telescope Astronomical tools Optical (visible light) telescopes Properties of optical telescopes Lightgathering power Larger lens (or mirror) intercepts more light Determines the brightness Resolving power The ability to separate close objects Allows for a sharper image and finer detail Optical (visible light) telescopes Properties of optical telescopes Astronomical tools Magnifying power The ability to make an image larger Calculated by dividing the focal length of the objective by the focal length of the eyepiece Can be changed by changing the eyepiece Limited by atmospheric conditions and the resolving power of the telescope Even with the largest telescopes, stars (other than the Sun) appear only as points of light A larger objective lens provides a brighter (not bigger) image Appearance of a galaxy in the constellation Andromeda using telescopes of different resolution Matching 10-m, multiple mirror Keck Telescopes in Hawaii with adaptive optics Not all EM radiation can penetrate Earth's atmosphere. Astronomical tools Detecting invisible radiation Photographic films are used to detect ultraviolet and infrared wavelengths Most invisible wavelengths do not penetrate Earth's atmosphere, so balloons, rockets, and satellites are used Radio radiation Reaches Earth's surface Radio wavelength observations are possible from Earth's surface Astronomical tools Detecting invisible radiation Radio radiation Gathered by "big dishes" called radio telescopes Large because radio waves are about 100,000 longer than visible radiation Often made of a wire mesh Have rather poor resolution Can be wired together into a network called a radio interferometer A steerable radio telescope at Green Bank, West Virginia Astronomical tools Detecting invisible radiation Radio radiation Gathered by "big dishes" called radio telescopes Advantages over optical telescopes Less affected by weather Less expensive Can be used 24 hours a day Detects material that does not emit visible radiation Can "see" through interstellar dust clouds The 300meter radio telescope at Arecibo, Puerto Rico The Very Large Array The Very Large Array (VLA) in New Mexico Astronomer's face two major obstacles in observing the stars
Light Pollution from Cities Effects of Twinkling from Earth's atmosphere Tucson, Arizona in 1959 and 1980 Rapid changes in the density of Earth's atmosphere cause passing starlight to quickly change direction, making stars appear to twinkle. Image of stars taken with a telescope on the Earth's surface Earth's atmosphere hinders astronomical research Same picture taken with Hubble Space Telescope high above Earth's blurring atmosphere High above Earth's atmosphere, the Hubble Space Telescope provides stunning details about the universe Deployment of the Hubble Space Telescope in Earth orbit, April 24, 1990 SOFIA
Stratospheric Observatory for Infrared Astronomy Advanced technology is spawning a new generation of equipment to view the universe
CCDs (chargecoupled devices) Large telescopes on remote mountain tops Adaptive Optics to counteract the blurring of Earth's atmosphere Orbiting space observatories Mauna Kea in Hawaii Cerro Pachon in Chile A Charge-Coupled Device (CCD) Ordinary Photographs vs. CCDs Observations at wavelengths other than visible light are revealing previously invisible sights Visible light image radio wavelength image Observations at other wavelengths are revealing previously invisible sights UV infrared Ordinary visible Map of Orion region What did you think?
What is the main purpose of a telescope? A telescope is designed to collect as much light as possible. It also improves resolution and magnifies images. Why do stars twinkle? Rapid changes in the density of Earth's atmosphere cause passing starlight to change direction, making stars appear to twinkle. Tools of Astronomy
End of Chapter 1: List the major regions of the electromagnetic spectrum in order of wavelength and give common examples of each. 2: List the colors of the visible spectrum in order of wavelength. 3: Name the two main classes of telescopes and describe the physical laws that each uses to form images. 4: Describe how the focal length and diameter of a telescope influence its angular resolution, lightgathering power, and magnifying power. 5: Draw a refracting telescope and reflecting telescopes with Newtonian, Cassegrain, prime, and coude' focus locations, showing the path of parallel light rays through each. 6: Compare the merits and deficiencies of the two major classes of telescopes. 7: Discuss the similarities and differences of radio telescopes and optical telescopes. 8: List the advantages of orbiting telescopes over Earthbound telescopes in detecting electromagnetic radiation in each of the major spectral regions. Self-Check Reflecting telescopes use mirrors to concentrate incoming starlight ...
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This note was uploaded on 08/07/2008 for the course GEO 1408 taught by Professor Greene during the Summer '07 term at Baylor.
- Summer '07