7. Radiation, Spectroscopy, And Telescopes

8/4/2019 7. Radiation, Spectroscopy, And Telescopes

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Radiation,

Spectroscopy, andTelescopesJ.T.II Olivar

Faculty of Arts and Letters

University of Santo Tomas

1st Semester AY 2011-2012


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Outline of the Lecture Telescopes

Electromagnetic (E-M) Spectrum


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First Telescopes The first refracting telescope is thought to

have been invented in 1608 by Hans

Lippershey. Italian scientist Galileo Galilei is credited

with making the first astronomical

observations sing a telescope in 1610. English scientist Isaac Newton built the

first reflecting telescope in 1671.


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Refracting TelescopeDesign: G. Galilei (1609)


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Because different components of lightare refracted differently, refracting

telescopes tend to produce images withcolor distortions.


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Reflecting TelescopeDesign: I. Newton (1670)


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Isaac Newtons reflecting telescope

solved the problem of color distortion

because all wavelengths of light arereflected equally.

Reflecting telescopes became the

standard form of modern opticaltelescopes.


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Other Designs of Telescopes:G. Cassegrain (1672)


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J. Gregory (1663)


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J. Kepler (1611)


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Maksutov (1944)


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B. Schmidt (1930)


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18th Century Telescopes New astronomical discoveries continued

as telescopes got larger, but it soon

became apparent that there was aphysical limit to their size.

German born astronomer William

Herschel, who lived in England, was animportant pioneer in the development ofthe telescope.


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Electromagnetic Radiation Energy is emitted by objects such as

stars and galaxies and transmitted

through space as electromagneticradiation (E-M radiation).

E-M radiation can be emitted along a

range of wavelengths from fewpicometers to tens of kilometers.


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Sensing these radiations withinstruments such as telescopes allows

scientists to learn about the objects thatemit them.

Visible light is just one part of the

spectrum of E-M radiation.


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The ElectromagneticSpectrum


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Ultraviolet (UV) Rays


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Radio Astronomy Radio astronomy is the collection and

analysis of radio waves emitted by

objects in space.


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Advantages of Radio Astronomy

Radio telescopes can detect much weaker

electromagnetic waves than opticaltelescopes.

Radio waves are emitted by some objectswhich emit no or little visible light and are

therefore invisible to optical telescopes.

Radio waves can travel through dust cloudsin space without being diffused.


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Disadvantages of Radio Astronomy

Long radio waves cannot penetrate the

Earths atmosphere so satellites must beused to study them.

Very large dishes are needed to focus radiowaves.


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[Examples of] RadioAstronomy Telescopes Steerable Dish Radio Telescopes

Fixed Dish Radio Telescopes

Radio Telescope Arrays


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Modern OpticalTelescopes The modern history of optical telescopes

has been the story of the quest to build

ever larger mirrors and the need tosituate them in remote, high altitudelocations away from light pollution.


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Hubble Space Telescope(HST) Optical telescopes on the Earths surface

suffer from distortions created by the

Earths atmosphere. The HST is an optical instrument placed

in Earths orbit above interference from

the atmosphere.


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Infrared Astronomy Infrared Radiation (IR) is essentially heat.

IR has wavelengths a little greater than

the extreme red limit of visible light. Almost all objects emit some heat

radiation, even if they are close to

absolute zero. Cool objects, such as dust clouds and

dead stars, emit some heat but no light.


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Ultraviolet (UV)Astronomy Ultraviolet (UV) Radiation is harmful to

living organisms on Earth much of it is

filtered out by the Earths ozone layer. UV radiation has wavelengths a little

shorter than the extreme blue limit of

visible light. Almost all objects emit UV radiation.


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X-Ray Astronomy The sun becomes the first X-ray source

to be imaged.


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Gamma Ray Astronomy Gamma rays are harmful to life on Earth

they are absorbed by the Earths

atmosphere. A gamma ray photon has over one

million times energy of a visible light

photon. Gamma rays have wavelengths much

shorter than the wavelengths of visible

light.


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Cosmic Ray Astronomy The most powerful form of energy in the

E-M spectrum.

Can have energies a billion times greaterthan those produced in particleaccelerators.

Direction of origin and accelerationprocesses are often difficult to assess.

Harmful to life on Earth their energy is

absorbed by the Earths atmosphere

7. Radiation, Spectroscopy, And Telescopes

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