Astronomical Instruments Chapter 6.ppt - Chapter 6 1...

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1Chapter 6
Ancient cultures built special sites, calledobservatories, for observing the skyAt theseobservatories, they were able tomeasure the positions of celestial objectsthat were visible to the naked eyeTelescopeswere first used to observe thesky byGalileo Galilei, and so theyare a relatively recent additionto the tools astronomers useThe use of telescopes, however,completely revolutionized ourideas about the universe2
Galileo first used a telescope toobserve the sky in 1610His telescopes were simple tubes held byhandThey were also small in comparison to thetelescopesin use todayThe use of these small telescopes allowedGalileo to revolutionize the field of astronomy3
Celestial objects — planets, stars, galaxies, etc. — emit(or reflect) light in many different directionsOnly aminuscule fractionof the light emitted (orreflected) by celestial objects is captured by the humaneye, with its tiny openingThe light not shining into the eye is “wasted”Most objects of interest to astronomers areextremelyfaintThe more light from such objects we can collect, the betterwe can study themAtelescopeis a very important tool because ithas a much larger opening than the human eye and,therefore,captures much more lightfocuses all the light collected into an imagemuch betterthan the naked eye can4
Stars and other celestial objects emit all typesof electromagnetic waves, not onlyvisible lightNowadays, there are types of telescopes thatcollect not visible light, but other forms of EMradiation, such asradio waves,infrared,ultraviolet,X-rays, and evengamma raysSuch telescopes may usecollecting devicesthat look very different from thelensesandmirrorsused invisible-lighttelescopes, butthose devices serve the same function5
In telescopes of all types, the light-gathering abilityis determined by the area of the device acting as themain collector of light (or other forms ofelectromagnetic radiation)Theapertureof a telescope with round lenses andmirrors corresponds to thediameterof itsprimarylensorprimary reflector(mirror)The light-gathering power of a telescope isdetermined by itsapertureThe amount of light a telescope can collect increaseswith the square of the apertureFor example, an aperture with a 4-meter diameter cancollect 16 times as much light as an aperture with a 1-meter diameter6
The study of astronomical objectsrequires the formation of their imagesOnce formed, each of the images can belooked at directly with the naked eyeimprinted on a photographic filmdetected and recorded with various light-sensitive devices7
Before the 20th century, telescope imageswere simply looked at with the naked eyeThis was a rather inefficient and unreliable way ofgathering/collecting and preserving the informationIn the 20th century, before the arrival ofcomputers, images were imprinted/recorded onphotographic filmsNowadays, astronomers actually rarely lookthrough the larger telescopesMost images are recorded electronically on computers8

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Term
Fall
Professor
Mr. Tabulov
Tags
Astronomy, Telescopes, Light, Telescope, Refracting telescope

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