ASTR - Chapter 6 Reading Notes
ASTR - Chapter 6 Reading Notes ASTR 11200
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This 11 page Class Notes was uploaded by Kara Ott on Friday September 18, 2015. The Class Notes belongs to ASTR 11200 at Rowan University taught by Andrew Watson in Fall 2015. Since its upload, it has received 21 views.
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Date Created: 09/18/15
Chapter 6 Telescopes 0 Basic components of our eyes pupil lens retina o Pupil controls how much light enters the eye I Dilates opens wider in low light I Constricts in bright light 0 Lens bends light to form image on retina o Retina contains light sensitive cells cones and rods when triggered by light that send signals to the brain Via the optic nerve o Refraction the bending of light that changes the direction in Which the light is traveling o Earth s atmosphere bends light The sun looks squished at sunset because light from the lower portion of the sun passes through more atmosphere and therefore bends slightly more than light from the upper portion 0 Focus focal point a point at which all the parallel rays of light converge after passing through a lens of your eye a telescope etc 0 Because of this sharp convergence of light this is why stars appear as points of light to us 0 Focal plane of the lens is where images appear in focus Detector part of camera that makes permanent records of an image when a camera lens bends light and brings the image to a focus Exposure time amount of time during which light collects on the detector exposure time is controlled by shutter Pixels grids of individual picture elements In science image processing is used to bring out details that might have remained hidden Telescopes are like giant eyes that collect more light 0 Light collecting area tells how much total light a telescope can collect at one time o Angular resolution the smallest angle over which we can tell that two dots or stars are distinct I Human eye has angular resolution of about 1 1 arcm1nute 5 mean1ng two stars can appear distinct only if they have at least this much angular separation in the sky I Interference of beams of light with each other limits the telescope s angular resolution I Diffraction limit angular resolution a telescope could achieve if it were limited only by interference of light waves 0 Depends on diameter of telescope s primary mirror and wavelength of light being observed 0 Diffraction limit is larger for longer wavelength light Refracting telescope operates like eye uses transparent glass lenses to collect and focus light Re ecting telescope uses precisely curved primary mirrors to gather light Mirror re ects gathered light to a secondary mirror that lies in front of it Secondary mirror then re ects light to focus at place where we can observe it Re ecting telescopes are used more in labs because o Refracters require higher quality and perfect glass 0 Large glass lenses are too heavy to stabilize and keep from deforming o 3 basic categories of telescope observations 0 Imaging photos of astronomical objects o Spectroscopy obtain and study spectra I Spectoqraphs are instruments that use diffraction gratings to separate various colors of light into spectra I The higher the spectral resolution the more detail we can see 0 Time monitoring how object changes with time I Light curves are graphs that show how an object varies with time o The brightness of our daytime sky and bright city lights are due to our atmosphere scattering the sunlight It drowns out the dim light of most astronomical units 0 Light pollution human made light that scatters the light and obscures our View of the night sky 0 Turbulence Winds and other air currents ensuring that air in our atmosphere is continually moving 0 This changes atmosphere s light bending properties 0 Adaptive optics technology that can eliminate much of the blurring of images by turbulence and allows telescopes to achieve angular resolution close to their diffraction limits 0 Turbulence makes rays of light dance around as they reach the telescope 0 Adaptive optics make telescope mirror do opposite dance cancelling out atmospheric distortion 0 Criteria for an observatory site or location for telescope 0 Dark no minimal light pollution 0 Dry to limit clouds and rain 0 Calm to limit turbulence 0 High to be above the densest part of the atmosphere 0 Sites of largest major telescopes o 4300 meter summit of Mauna Kae o 2400 meter site on island of La Palma o 2600 meter Paranal Observatory Site Our atmosphere prevents most forms of light from reaching the ground at all Planets are cool and emit primarily infrared light Hot upper layers of stars like the Sun emit ultraviolet light and X rays Only radio waves visible light and small parts of the infrared spectrum can be observed from the ground 0 That s why we put telescopes out in space Basis idea behind telescopes to collect as much light as possible with as much resolution as possible The most common type of telescope in the world is a radio telescope Infrared telescopes generally look the same as visible light telescopes Two major ultraviolet observatories in space 0 Galaxy Evolution Explorer GALEX o Hubble Space Telescope Grazing incidence mirrors are designed to slightly de ect x rays so that they just graze the surfaces of their mirrors Telescopes used to detect gamma rays are massive sometimes around 3 tons Other types of cosmic messages besides light 0 Neutrino produced by nuclear reactions ex nuclear fusion 0 Cosmic rays not much known about origin 0 Gravitational waves o InterferometrV uses 2 telescopes to achieve angular resolution of much larger telescopes and takes advantage of wavelike properties of light that causes interference