PowerPoint PresentationSlide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Issues with the use of telescopesMagnificationMagnification determines how much larger the image is as compared to the size of the source of the light (the object)Magnification =fo fe Where fo is the focal length of the objective fe is the focal length of the eyepieceIssues with the use of telescopesMagnificationFrom the group exercises, most of the object the average observer would look at at actually relatively large.Magnification is not the most important characteristic of a telescope for a backyard astronomer.Professional astronomy also requires the examination of deep sky objects, which require a high magnification.Issues with the use of telescopesMagnificationFurther problems – if the image produced by the telescope does not accurately represent the source, and high magnification might only magnify the inaccuracies.The crucial issue - RESOLUTIONIssues with the use of telescopesResolutionMore important (possibly more important) than magnification is resolution.Resolution – the property of an instrument to identify (resolve) small details.The smallest angular size identifiable by an instrument is given bymin = .25DWhere is the wavelength of the EM waves being collected in m (1 m = 10-6 m)D is the diameter of the aperture (the opening which collects the wave) in metersThe calculated value of will be in seconds of arc (arc seconds)Issues with the use of telescopesResolutionmin is called the diffraction limited resolution of the telescopeIssues with the use of telescopesResolutionThe ability to resolve small details is determined by the wavelength fo the EM wave and the diameter of the aperture.For high resolution, one would observe as the shortest wavelength possible and use the largest diameter aperture possible.For a telescope, the diameter of the aperture is determined by the diameter of the objective.min (in arc sec) = .25 (in m )D (in m)Issues with the use of telescopesResolutionFor the naked eye, Shortest visible wavelength 400 x 10-9 m = .4 m Diameter of the aperture (the pupil) 3 mm = 3 x 10-3 mmin 33” = .55’ = .0093o The average human eye can resolve object with an angular diameter of about a half a minute. Compare with your estimate from Group Exercise 2min (in arc sec) = .25 (in m )D (in m)Issues with the use of telescopesResolutionFor the Mount Palomar 200 inch optical telescope, Shortest visible wavelength 400 x 10-9 m = .4 m Diameter of the aperture (the objective) = 200 in = 5.08 mmin 1.96 x 10-2 “ = 3.2 x 10-5 ‘ = 5.5 x 10-7 degreesThe Mount Palomar telescope can resolve objects about 1700 times smaller than the naked eye min (in arc sec) = .25 (in m )D (in m)Issues with the use of telescopesResolution – The Hubble Space TelescopeHubble works on the same principle as the first reflecting telescope built in the 1600s by Isaac Newton. Light enters the telescope and strikes a concave primary mirror, which acts like a lens to focus the light. The bigger the mirror, the better the image. In Hubble, light from the primary mirror is reflected to a smaller secondary mirror in front of the primary mirror, then back through a hole in the primary to instruments clustered behind the focal plane (where the image is in focus). Mirror sizePrimary mirror: 2.4 m – (94.5 inches) in diameterSecondary mirror: 0.3 m - (12 inches) in diameter Angular resolutionHubble's angular resolution is 0.05 arcsecond. This is the "sharpness" of Hubble's vision. If you could see as well as Hubble, you could stand in New York City and distinguish two fireflies, 1 m (3.3 feet) apart, in San Francisco.Issues with the use of telescopesResolutionIf the Mount Palomar 200 inch optical telescope recorded radio waves of wavelength 1 meter, wavelength 1 m = 1 x 106 m Diameter of the aperture (the objective) = 200 in = 5.08 mmin 4.9 x 104 “ = 820’ = 13.7o The angular diameter of the moon = 30’ The angular diameter of the Andromeda Galaxy 178’The Mount Palomar telescope would not be able to resolve these objectsIt would not be able to “see” the moon ! min (in arc sec) = .25 (in m )D (in m)Issues with the use of telescopesResolutionFor the National Radio Astronomical Observatory Robert C. Byrd Radio Telescope, wavelength 1 m = 1 x 106 m Diameter of the aperture (the objective) = 100 mmin 2500” = 41’ = .69o The angular diameter of the moon = 30’ The angular diameter of the Andromeda Galaxy 178’The NRAO telescope would be able (roughly) to resolve radio sources of these angular diametersThis is the worlds largest fully steerable radio telescope min (in arc sec) = .25 (in m )D (in m)Issues with the use of telescopesResolutionFor the Arecibo Radio telescope, wavelength 1 m 1 x 106 m Diameter of the aperture (the objective) = 305 mmin 819” = 13.7’ = .22o The angular diameter of the moon = 30’ The angular diameter of the Andromeda Galaxy 178’The Arecibo telescope would easily be able to resolve radio sources of these angular diametersHowever, the Arecibo telescope can only “see” object directly above itmin (in arc sec) = .25 (in m )D (in m)Difficulties:* Physical size of long focal length objectives* Absorption of light by the lenses* Grinding two precision surfaces* Chromatic and spherical aberrationsIssues with the use of telescopesRefractorsAdvantages:Compound telescopes with long focal length objectives can be relatively compactSingle ground surfaceDisadvantage:MUST have an obstruction in the pathIssues with the use of telescopesReflectorsIssues with the use of telescopesWide Field TelescopesDesigned in 1930 by Bernhard Schmidt, the Schmidt Camera was the forerunner of the modern Schmidt-Cassegrain telescope. Notwithstanding all of the advances in optical and electromechanical technology over the intervening years, however, the classical Schmidt Camera to this day accomplishes feats of astrophotography that are simply unattainable with any other telescopic lens, telescope, or electronic imager. No other photo-optical instrument permits such extremely wide-field photography at such fast photographic speed and with such an amazingly flat imaging
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