Cosmic Messenger

7/28/2019 Cosmic Messenger

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Learnin from Li hLearnin from Li h

Types of TelescopesTypes of Telescopes

EE8086EE8086 Astronomy: Stars, Galaxies & CosmologyAstronomy: Stars, Galaxies & Cosmology p.3-1

Further Reading:Further Reading:The Essential Cosmic Perspective, Chapters 5The Essential Cosmic Perspective, Chapters 5


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Light: The Cosmic MessengerLight: The Cosmic Messenger

nc en o servers eep rac o

time & seasons, navigate &su e eavens oo n alight fromthenightsky.

Earl observers coul onldiscern the most basic featuresof the light the saw, such as

colour & brightness.Over the past several hundred years, we have discovered that

li h carrie fa mor information.

Today, light of distant objects are analyzed to learn what they

, ,muchmore.


L ght br ngsstor eso d stant ob ectstoEarth.


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What is Light?What is Light?

Nature of light remaine

myster until recentl inhuman

history.

white light is made up of aspec rumo co ours n s.

prior to that, many thought the

colourscame romtheprism

visiblelight isonlyatinypartof thecomplete

thereisalso lightthatour eyescannotcannotseesee



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Nature of LightNature of Light

aveNature

Particle

NatureLight is form of energy transport consisting of

electroma neti wave travelin a th s ee of li h . nomassisexchanged& nomediumisrequired

g t asa ua nature: wavewave part c epart c e.

demonstrated by physics experiments over the past hundred


yearsor so


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Wave Nature of LightWave Nature of Light

Wave is a disturbance that transmit

energy through space & time withoutcarryingmaterial alongwithit.

Light is an electromagneticwav . can affect both chargedcharged

articlesarticles& ma nema ne



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Wave Nature of Light, contdWave Nature of Light, contd

Shorter wavelength Longer wavelength

Higher frequency Lower frequency

Light travel through empty space at the same speed of

c=3108 m/s.

f fre uenc of li h (Hz) & wavelen thof li h (m)



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Particle Nature of LightParticle Nature of Light

L g taso avepart c epropertes.

packetsof energycalledphotons.

eac o ona so rave a e pee o a photon has no electric charge or mass but possesses

momenummomenum energyenergy

Ener of each hoton isproportional to frequency . thehigher thefrequency(the

,higher thephotonenergy


c =


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Electromagnetic Spectrum: The Many Forms of LightElectromagnetic Spectrum: The Many Forms of Light



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What is Matter?What is Matter?

We are intereste in the matter of planets, stars &

alaxies. obviouslynotpractical tostudytheseobjectsbygoingtothem

L g t can interacinterac w t t ese matte & n ormatonaboutthemarecarriedacrosstheuniverse. need to understand thenatureof matter beforeyou can decode

theinformationreceivedinlight

Matter aremadeupofatoms.

more than 100 different types of atoms, known as chemicalelements (periodicperiodictabletable)

atoms are in turn made up of particles called protons (+(+vevecharge)charge), neutrons(no(nocharge)charge) & electrons((--vevecharge)charge)



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Structure of a Typical AtomStructure of a Typical Atom

Properties of atom depend

chargein thenucleus.

A drop ofwater has

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t m .EE8086EE8086 Astronomy: Stars, Galaxies & CosmologyAstronomy: Stars, Galaxies & Cosmology p.3-10


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Atomic TerminologyAtomic Terminology

Each different chemical element contains differen protonnumber inthenucleus.

calledtheatomicatomicnumbernumber proton+neutron==atomicatomicmassmassnumbernumber

Atomsof anelementwithdifferent


.


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LightLight--Matter InteractionsMatter Interactions

FouFou waysways nw c g tcan nteractw t matte :

matter releasesenergyaslight

Absorption matter takesenergyfromlight

Transmission ma er a ows o ass rou

Reflection

lightbounceoff matter toanother direction

aer as a transmit lightaresaidtobetransparenttransparent


absorblightarecalledopaqueopaque


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Thermal RadiationThermal Radiation

Thermal

a a onSpectra

Nearly all large or dense objects emit thermal

radiation, includingstars, planets& evenyou. thermal radiationisalsoknownasablackbod radiation

Anobjects thermal radiationspectrumdependsononly


oneproperty: ts empera ure.

L f Th l R di iL f Th l R di i


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Laws of Thermal RadiationLaws of Thermal Radiation

The thermal radiation of an object is described by two

StefanStefan--BoltzmannBoltzmann LawLaw A hotter objectssurfaceemits

more ig t per square meter at a waveengt s. T e totalenergy radiated per unit surface area varies as the fourth

power o t eo ectstemperature .

WiensWiens LawLaw Hotter objects emit photons with a higher, . . .

wavelength of thermal radiation spectrumis inversely related .


St fSt f B lt LB lt L


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StefanStefan--Boltzmann LawBoltzmann LawTwo stars of the

will emit4timesthe total

energy of thesmaller star.Small star ishalfthe

size of the lar e sta

Surface area of

= 2

A hotter objects surface emits more light per square.

per unit surfacearea varies as thefourth power of the


.

Wi LWi L


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Wiens LawWiens Law

Hotte objects emit photons with highe averageener i.e. shorte avera e wavelen th. Peakwavelength of thermal radiation spectrum is inversely


.


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Which star ishotter?


Typesof Light SpectraTypesof Light Spectra


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Types of Light SpectraTypes of Light Spectra


Energy Levelsin AtomsEnergy Levelsin Atoms


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Energy Levels in AtomsEnergy Levels in Atoms

Electron energies are

on certaindiscrete values

Electrons inanatomcanonly haveparticular amountofenergy& notothersinbetween. lowestenergylevel iscalledthegroundstate


higher energ levelsareknownasexcitedstates

EnergyLevel TransitionsEnergyLevel Transitions


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Energy Level TransitionsEnergy Level Transitions

Electron gaining enough energy to

reach ionization level escapefrom

Electron energy

is measured in.

becomes charged & are called ions.

unit for energy, J )

Hydrogen

atom


Origin of Emission & Absorption LinesOrigin of Emission & Absorption Lines


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Origin of Emission & Absorption LinesOrigin of Emission & Absorption Lines

The spectral lines are due to the unique set of discreteenerg levels fo eachtypeof atom, iono molecule.

uni ue s ectral fin er rint can be use to identif the


chemicalsincelestial objects

Spectral Linesof Different ElementsSpectral Linesof Different Elements


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Spectral Lines of Different ElementsSpectral Lines of Different Elements

Compares with spectral lines of

known elements to infer thecomposition of an celestial object.

o arSpectrum


Doppler EffectDoppler Effect


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Doppler EffectDoppler Effect

ounoun

c angec ange nn requencyrequency w vfor anobserver movingrelativetothesourceof thewave.


amounto s t sproport ona tot ereat veveoc t

How dowetell theSpeed of aDistant Object?How dowetell theSpeed of aDistant Object?


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How do we tell the Speed of a Distant Object?How do we tell the Speed of a Distant Object?

=


Doppler Shift & Lineof SightDoppler Shift & Lineof Sight


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Doppler Shift & Line of SightDoppler Shift & Line of Sight

Radialvelocity

Tangentialvelocity


MeasuringRotational VelocityMeasuringRotational Velocity


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Measuring Rotational VelocityMeasuring Rotational Velocity

The Doppler effect broadens the widths of the spectral lines of rotatingobjects. One side of a rotating object is moving toward us creating a


ues t, w et eot er s e srotat n awa romus, creatn are s t.

CollectingLight with TelescopesCollectingLight with Telescopes


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Collecting Light with TelescopesCollecting Light with Telescopes

Wecanonly seealittleamountof light whenwelook at the

skywithour nakedeyes.

Telescopes are essentially giant eyes,

allowing us to see muchmuch fainterfainter.

specify in terms of lightlight--collectingcollectingareaarea& angularangular resolutionresolution

scientifi instrument ca b

connected to analyze the light (visibleor invisible the collect


a eos eescope

Bigger is BetterBigger is Better


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Bigger is BetterBigger is Better


Types of TelescopeTypes of Telescope


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ypeso eescopeypeso eescope

eescopescome n wo asc esgns:

Refracting telescope uses lenses

Reflecting telescope uses curvedmirrors to collect & focus light(used exclusively in professionalastronom today)


Refracting TelescopesRefracting Telescopes


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g pg p

A large convex lensconcentrates light from adistant object to the focus.

lens that enables the eyeto view a magnifiedversion of the imageproduced.

erkes1mrefractin telesco e:

University of Chicago, US


largest refractor in the world

Reflecting TelescopesReflecting Telescopes


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g pg p

The primary mirror reflects light to a

Gemini North telesco e:

secondary mirror before focusing it to ahole in the primary mirror. The image is


8 m diameter primary mirror.

Alternative Design of Reflecting TelescopesAlternative Design of Reflecting Telescopes


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g g pg g p


Other Reflecting TelescopesOther Reflecting Telescopes


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g pg p

The most powerful telescope on the

summit on Mauna Kea, Hawaii, is,has 10 m diameter mirror made upof36 hexagonal segmentsthat

effectively work as a single piece ofreflective glass.

The telescopes can operate

together to form a single,

which can probe structures withhigher resolutionhigher resolution by means of


interferometry.

Telescopes Across the SpectrumTelescopes Across the Spectrum


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Arecibo radio telesco e thelargest single telescope inthe world, stretches305 m

across a natural valley inPuerto Rico.

Telescopes for otherother wavelengthswavelengths of light allow us to learn.

telescopesfor nonvisiblelightrequireadifferentdesign

ong waveengt ra o wave teescopes ave to e verylargetoachievereasonableangular resolution.


resolutionisproportional towavelength

Other Radio TelescopesOther Radio Telescopes


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Very Large Array (VLA)Very Large Array (VLA) in Newin New

out inout inYY shape for interferometricshape for interferometric

is equivalent to a single telescopeis equivalent to a single telescopewith a diameter of 40 km.with a diameter of 40 km.


Interferometry


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Two (or more) radiodishes

observethesameobject.

Their signals are made to.

An image is reconstructedwith theangular resolution

one would get froma dishthe size of the distancebetweenthem.

light-collecting area is stillonl thesumof theareasoftheindividual dishes


Atmospheric AbsorptionAtmospheric Absorption


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roun - ase teescopes atwavelengths outside the transmission

windows are completely useless!


Observatories in the SkyObservatories in the Sky


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Satellites belonging to the NASAs Great ObservatoryProgram for the observation of distant planets, galaxies &


ot er outer-spaceo ects.

SpaceSpace--Based Telescopes (Based Telescopes (--ray)ray)


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-

Launchedin1991.


e erae e-or e e no e ac c cean n .

SpaceSpace--Based Telescopes (XBased Telescopes (X--ray)ray)


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ard.e

du

dra.ha

r

p://chan

htt

SubrahmanyanChandrasekhar

- -

(1910 1995)

.

Launchedin1999.


SpaceSpace--Based Telescopes (UV, Visible, NIR)Based Telescopes (UV, Visible, NIR)


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ite.org/

hubbles

http

:/

win Hu e(1889-1953)

HubbleSpaceTelescope: detectsUV, visible, NIR.aunc e n .

TobereplacebyJ amesJamesWebbWebbSpaceSpaceTelescopeTelescope,


ueto e aunc e n .

J ames Webb Space TelescopeJ ames Webb Space Telescope


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(1906-1992)

Instrumentshavewavelengthcoveragefrom0.6to28m.

Primaril look attheuniverseintheinfrareinfrare .


SpaceSpace--Based Telescopes (IR)Based Telescopes (IR)


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Spitzer Space Telescope:

detectsIR from3~180m.

Launchedin2003. Lyman Spitzer(1914-1997)

Messier 81, a s iral alax


12mmlight-years away.

Why do we put Telescopes in Space?Why do we put Telescopes in Space?


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telescope coverlightenters

solarpanels

secondary

mirror

primarymirror

Despite the relatively smallsize of Hubble Space

Telescopes primary mirror

scientific

instruments

(2.4 m diameter), it

performs much better thanarger ameter groun -based telescopes at visible


waveen s.

Atmospheric Effects on Visible LightAtmospheric Effects on Visible Light

r nesso e a mes m

sv s e o serva on


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r nesso e a mes m sv s e- o serva on

tothenight.

no such problemwith radio telescopes, which can observe both

Scattering of man-made lights by the atmosphere makes the


ng ts r g ter light pollution.

Atmospheric Effects on Visible Light, contdAtmospheric Effects on Visible Light, contd


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.

bendslight inconstantlyshiftingpatterns


causestwn n o stars

Advanced Telescopic ObservationAdvanced Telescopic Observation

h b hi l i


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The observatory can shine a laser intothe sky to create an artificial star (a

can monitor for atmospheric distortions.

byatmosphere.

changingatmosphericdistortion


abrightstar or artificial star createdbylaser

Cosmic Messenger

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