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Atron1F03 Chapter 3.docx - CHAPTER 3: TELESCOPES 1. OPTICAL...

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CHAPTER 3: TELESCOPES1.OPTICAL TELESCOPESTelescope:“light bucket”- device whose primary function is to capture as much radiation aspossible from a given region of the sky and concentrate it into a focused beam for analysisReflecting and Refracting Telescopes2 basic categories of optical telescopes:1)Reflecting Telescope: uses curved mirror to gather and concentrate a beam oflightMirror is called a primary mirror – constructed so that all light rays canarriving parallel to its axis are reflected to pass through a single point =focusAxis:imaginary line through center and perpendicular to mirrorFocal length: distance between primary mirror and focusPrime Focus:focus of primary mirror2)Refracting Telescope: uses a lens instead of mirror to focus incoming light –relies on refractionRefraction:bending of beam of light as it passes from one transparentmedium to anotherAstronomers use telescopes to create images of their viewLight from a distant object reaches telescope as nearly parallel raysRay of light entering instrument parallel to the mirror is reflected to focusLight from different direction, at angle, is focused at different pointImage is formed near focusEye Piece: lens – used to magnify the imageAstronomers Favor reflecting instruments b/c of following refracting disadvantages:1)Lens focuses red and blue light differently = chromatic aberration, although itcan be fixed it requires use of high quality glass2)Light passes through the lens, some of it is absorbed by glassAbsorption is relatively minor problem for visible radiation but can besevere for infrared and UV observations3)Large lens is heavy4)Lens has 2 surfaces that must be accurately machines and polished which is adifficult task2.DETECTORS AND IMAGE PROCESSINGModern telescopes use electronic detectors called: charge coupled devices(CCDs) torecord and store dataConsists of: wafer of silicon divided into 2-D grid of many tiny picture elements (pixels)When light strikes pixel, an electric charge builds up on the deviceAmount of charge is directly proportional to the number of photons striking the pixelSame as used in phonesAdvantages of CCD than photographic plates:
Astronomy Textbook NotesMuch more efficient – can image object 10 to 20 times fainterProduce a faithful representation of an image in digital format that can be manipulatedby other technology (computers)

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Term
Spring
Professor
wadsley

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