AstronomicalObservingTechniques

Lecture3:EyestotheSkies

ChristophU.Keller

keller@strw.leidenuniv.nl

Outline

1.  Poin8ngTelescopesonEarth2.  SpaceTelescopeOrbits3.  Op8calTelescopes4.  RadioTelescopes,Interferometers

5.  X-rayandGamma-RayTelescopes

6.  NeutrinoTelescopes7.  Gravita8onalWaveTelescopes

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EarlyTelescopes

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•  HansLipperhey1608:spyglasses

•  GalileoGalilei1609:firstuseinastronomy

•  Kepler1611:improvedrefractor

Newton1668:firstreflector

Herschel1789:1.22-mdiameter,12-mlong

Equatorialmount

+lightandsymmetric+fixedgravityonbearings+twofixed-gravityports-twomovingaxes-imagerota8on

+singlemovingaxis+constantrota8on+noimagerota8on-large,heavy-instruments:varyinggravity

TelescopeMounts

Azimuthalmount

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CTIO 4-m, www.noao.edu/image_gallery/html/im0132.html WIYN 3.5-m www.noao.edu/image_gallery/html/im0525.html

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Azimuthal Telescope Mounts SALT

VLT www.eso.org/public/archives/images/screen/vlt-Inside-c-cc.jpg

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Orbits-  lowEarth-  sun-synchronous-  geosta8onary-  Earth-trailing-  L2

HST : low Earth orbit ~96 minutes Spitzer: Earth-trailing solar orbit ~60 yr

Orbitchoiceinfluencedby-  communica8ons-  thermalbackgroundradia8on-  spaceweather-  skycoverage-  access(servicing)

SpaceTelescopeOrbits

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LagrangianPoints

map.gsfc.nasa.gov/mission/observatory_l2.html

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JWST,WMAP,GAIA,HerschelinorbitsaroundL2+sun-shields-orbitaroundL2-radia8on

L2

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Scale: flfl ωωω 0175.0 : smallfor and tan ≈=

Magnifica8on:1

2

2

1

2

1 ωω===

DD

ffV

TelescopeOp@cs

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Hollandsche Kijker

limitations: field, chromatic aberrations

f1f2

magnifica8on=f1/f2

entrance pupil

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Kepler Refractor

•  larger FOV •  image upside down

f1 f2

magnifica8on=f1/f215-2-2016 Astronomical Observing Techniques 2016: Telescopes 12

SphericalLenses

Spherical Aberration: Beams away from center have shorter focal lengths

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•  providelargefieldofview(FoV)

•  raysmoredistantfromop8calaxishaveadifferentfocalpoint

SphericalMirrors

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Made w

ith Touch Optical D

esign

Parabolicprimarymirrorsfocusallraysfromthesamedirec8ontoonepoint.But:differentdirec8onshavedifferentfocalpoints.

v

ParabolicMirrors

àFieldofviewlimitedbyaberra8ons:thebiggerthemirrorthebiggerthedifference[parabola–sphere]neartheedgeàbiggertelescopeshavesmallerFOVs(~<1deg)15-2-2016 Astronomical Observing Techniques 2016: Telescopes 15

SchmidtTelescopeIdea:

1.  Usesphericalprimarymirrorformaximumfieldofview(>5deg)ànooff-axisasymmetrybutsphericalaberra8ons

2.  correctsphericalaberra8onswithcorrectorlens.

TwometerAlfred-Jensch-TelescopeinTautenburg,thelargestSchmidtcameraintheworld.

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Two-MirrorTelescopes

Newtonian Cassegrain Gregorian Three Mirror Anastigmat (TMA)

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Modifica8onofCassegrainconfigura8on(parabolicprimary,ellip8calsecondary):Hyperbolicprimarymirror(almostparabola)andhyperbolicsecondarymirroreliminates(some)op8calerrors(3rdordercomaandsphericalaberra8on).

à largefieldofview&compactdesign(foragivenfocallength)

Ritchey-Chré@enConfigura@on

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Ritchey-Chrétien Telescopes

VLT (4x)

GTC Subaru Keck (2x) Gemini (2x)

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Ritchey-Chrétien Telescope

HST

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TMA Wide-Field Telescope

Large Synoptic Survey Telescope (LSST)

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LightGatheringPowerandResolu@onLightgatheringpower

Forextendedobjects: (seelectureonS/N)

Forpointsources:Angularresolu8on

(givenbytheRayleighcriterion)

2

/ ⎟⎟⎠

⎞⎜⎜⎝

⎛∝

fDNS

2/ DNS ∝

Df

Dλλ

22.1lor 22.1sin =Δ=Θ

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Primefocus–widefield,fastbeambutdifficulttoaccessandnotsuitableforheavyinstrumentsCassegrainfocus–moveswithtelescopes,smallfield

TelescopeFoci–wheretoputtheinstruments

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Nasmyth–idealforheavyinstrumentstoputonastableplarorm,butfieldrotatesCoudé–veryslowbeam,usuallyforlargespectrographsinthe“basement”

TelescopeFoci–wheretoputinstruments(2)

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Dλ22.1sin =Θ

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GrowthofTelescopeCollec@ngArea

MassLimita@ons

biggermirrorsrequire•  thinner/segmentedmirrors•  ac8vesupport

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Segmented,ThinandHoneycombMirrors

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Ac@veMirrorSupport

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Op@calTelescopesinComparison

Palomar Keck JWST

Telescopeaperture 5m 10m 6.5m

Telescopemass 600t 300t 6.5t

#ofsegments 1 36 18

Segmentsize 5m 1.8m 1.3m

Mass/segment 14’500kg 400kg 20kg

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Arecibo, Puerto Rico – the largest (305m) single-aperture telescope Dishes similar to optical telescopes

but with much lower surface accuracy

Effelsberg, Germany – 100m fully steerable telescope

Greenbank, USA – after structural collapse (now rebuilt)

RadioTelescopes

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VLA in New Mexico – 27 antennae (each 25m) in a Y-shape (up to 36 km baseline)

ArraysandInterferometers

ALMA in Chile – 50 dishes (12m each) at 5000m altitude 400µm – 3mm (720 GHz – 84GHz)

WSRT (Westerbork) in Drenthe – 14 antennae along 2.7 km line

LOFAR in the Netherlands Arecibo •  LOwFrequencyARrayusestwotypesoflow-

costantennae:• LowBandAntenna(10-90MHz)• HighBandAntenna(110-250MHz).

•  Antennaeareorganizedin36sta8ons•  over~100km.Eachsta8oncontains•  96LBAsand48HBAs•  Baselines:100m–1500km•  MainLOFARsubsystems:• sensorfields• wideareanetworks• centralprocessingsystems• userinterfaces

• X-raysimpingingperpendicularonanymaterialarelargelyabsorbedratherthanreflected• telescopeop8csbasedonglancinganglereflec8on(ratherthanrefrac8onorlargeanglereflec8on)• typicalreflec8ngmaterialsforX-raymirrorsaregoldandiridium(goldhasacri8calreflec8onangleof3.7degat1keV).

X-rayTelescopes

Gamma-RayTelescopes

Fig. 1 in arxiv.org/pdf/0902.1089v1.pdf

FERMI satellite MAGIC Cerenkov telescopes

magic.mpp.mpg.de/newcomers/introduction/

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RHESSIGamma-Ray

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hesperia.gsfc.nasa.gov/rhessi3/mission

NeutrinoTelescopesneutrino.kek.jp/figures.html

Super-Kamiokande, 50,000 tons of water

www.sno.phy.queensu.ca/sno/images

Sudbury Neutrino Observatory, 1000 tons of D2O

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NeutrinoDetec@on

•  scaxeringofneutrinosonelectrons:e-+νeèe-+νe

•  electronacceleratedtov>cèCerenkovradia8on

•  solarneutrinos•  neutrinooscilla8ons•  neutrinosfromSN1987A

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NeutrinosinIceandWater

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gallery.icecube.wisc.edu antares.in2p3.fr/Gallery

IceCube at the South Pole ANTARES in Mediterranean Sea

Gravita@onalWaveDetectors

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GWMeasurementPrinciple

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ligo.org/science/GW-Overview/images/IFO.jpg