astronomical observing techniques lecture 3: eyes to the...
TRANSCRIPT
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