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Lesson 4 - Techniques in Astronomy - Techniques Astronomy...

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Techniques AstronomyTelescopesTelescopes are a key tool for astronomical research since first use by Galileo in 1609Early telescopes were known asrefractingtelescopesMost common modern forms of telescopes are calledreflectingtelescopesRefracting TelescopeRefracting telescope – Telescope using a glass lens as main light collecting elementLargest refracting telescope: 1m refractor telescope is located at Yerkes Observatory, ChicagoProblem: Lens has to be mounted at the top of the telescope tube1m glass is very heavy and must be supported only at edges to allow starlight throughoNot feasible making refracting telescopes bigger than 1m apertureoLens deform under own weightObjective lens defines an aperture of the telescopeEyepiece magnifies an imageReflecting TelescopesReflecting telescopes – Curved mirror to focus lightMost common design for modern telescopesMirror can be supported at its back as well as sides allowing for a larger mirror and hold it steadilycompared with lens
Telescope mirrors are made of large blocks of glass or ceramic material that’s ground down and polished toprecise curved shapeCoated with reflecting layer of silver/aluminium to get mirror surfaceMain mirror mounted at bottom end of telescope tubeoSmaller secondary mirror at top reflects light down to instruments mounted behind back ofmirroroLight reaches instruments through hole in primary mirrorKey FeaturesLight collecting power– Determined by area of collecting mirror or lensDepends onapertureApertureDiameter of mirror or lensLens twice as big will collect 4 times as much light because it has four times the areaBigger telescopes collect more lightSee fainter stars or galaxiesResolving power/angular resolution – Telescope’s ability to see fine detailAbility to resolve two nearby stars to see them as two separate stars rather than oneDependent on telescope apertureDevelopment of Telescope in Modern TimesMount Wilson 100”One of the first big telescopes: 100 inch telescope at Mt. Wilson Observatory nr. Los Angeles2.5 m in diameter; completed in 1917Edwin Hubble used for his work on distances of galaxies5m Hale Telescope5m telescope at Mt. Palomar, CaliforniaBuilt in 194810m Keck Telescopes, Mauna Kea HawaiiRecently, bigger telescopes have been built. Number of telescopes have aperture 8m – 10m2 x 10m telescopes mounted next to each otherUse interesting primary mirror design – Segmented mirroroMirror is built up from many hexagonal segments joined together making 10m mirroracrossExtremely Large Telescopes
Larger telescopes are called extremely large telescopes (ELTs)Have apertures of 20 – 40mThirty Metre Telescopes (TMT)Giant Magellan Telescope – Seven 8.4m mirrorsAperture of 24.5 m

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Term
Three
Professor
Bailey
Tags
Telescopes, Light, Telescope, Refracting telescope, spectral lines

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