Astronomical Observing Techniques Lecture 3: Eyes to the Skies

AstronomicalObservingTechniques
Lecture3:EyestotheSkies
ChristophU.Keller
[email protected]
Outline
1.  Poin8ngTelescopesonEarth
2.  SpaceTelescopeOrbits
3.  Op8calTelescopes
4.  RadioTelescopes,Interferometers
5.  X-rayandGamma-RayTelescopes
6.  NeutrinoTelescopes
7.  Gravita8onalWaveTelescopes
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EarlyTelescopes
•  HansLipperhey1608:
spyglasses
•  GalileoGalilei1609:
firstuseinastronomy
•  Kepler1611:
improvedrefractor
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Newton1668:
firstreflector
Herschel1789:
1.22-mdiameter,12-m
long
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TelescopeMounts
Equatorialmount
Azimuthalmount
+singlemovingaxis
+constantrota8on
+noimagerota8on
-large,heavy
-instruments:varyinggravity
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+lightandsymmetric
+fixedgravityonbearings
+twofixed-gravityports
-twomovingaxes
-imagerota8on
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CTIO 4-m, www.noao.edu/image_gallery/html/im0132.html
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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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SpaceTelescopeOrbits
Orbitchoiceinfluencedby
Orbits
-  lowEarth
-  sun-synchronous
-  geosta8onary
-  Earth-trailing
-  L2
- 
- 
- 
- 
- 
HST : low Earth orbit ~96 minutes
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communica8ons
thermalbackgroundradia8on
spaceweather
skycoverage
access(servicing)
Spitzer: Earth-trailing solar orbit ~60 yr
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LagrangianPoints
map.gsfc.nasa.gov/mission/observatory_l2.html
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L2
JWST,WMAP,GAIA,HerschelinorbitsaroundL2
+sun-shields
-orbitaroundL2
-radia8on
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TelescopeOp@cs
Scale:
tan ω =
l
f
Magnifica8on:
f1 D1 ω2
V=
=
=
f 2 D2 ω1
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and for small ω :
l ≈ 0.0175ωf
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Hollandsche Kijker
entrance pupil
f1
f2
magnifica8on=f1/f2
limitations: field, chromatic aberrations
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Kepler Refractor
•  larger FOV
•  image upside down
f1
f2
magnifica8on=f1/f2
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SphericalLenses
Spherical Aberration: Beams away from center have shorter focal lengths
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SphericalMirrors
•  providelargefieldof
view(FoV)
•  raysmoredistantfrom
op8calaxishavea
differentfocalpoint
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ParabolicMirrors
Parabolicprimarymirrorsfocusallraysfromthesamedirec8onto
onepoint.
But:differentdirec8onshavedifferentfocalpoints.
v
àFieldofviewlimitedbyaberra8ons:thebiggerthemirrorthe
biggerthedifference[parabola–sphere]neartheedgeàbigger
telescopeshavesmallerFOVs(~<1deg)
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SchmidtTelescope
Idea:
1.  Usesphericalprimarymirrorfor
maximumfieldofview(>5deg)ànooffaxisasymmetrybutsphericalaberra8ons
2.  correctsphericalaberra8onswith
correctorlens.
TwometerAlfred-JenschTelescopeinTautenburg,the
largestSchmidtcamerainthe
world.
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Two-MirrorTelescopes
Newtonian
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Cassegrain
Gregorian
Three Mirror Anastigmat
(TMA)
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Ritchey-Chré@enConfigura@on
Modifica8onofCassegrainconfigura8on(parabolicprimary,ellip8cal
secondary):Hyperbolicprimarymirror(almostparabola)andhyperbolic
secondarymirroreliminates(some)op8calerrors(3rdordercomaandspherical
aberra8on).
à largefieldofview&compactdesign(foragivenfocallength)
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Ritchey-Chrétien Telescopes
VLT (4x)
GTC
15-2-2016
Subaru
Keck (2x)
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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@on
Lightgatheringpower
2
⎛D⎞
Forextendedobjects:
S / N ∝
⎜⎜ ⎟⎟ (seelectureonS/N)
⎝ f ⎠
S / N ∝ D2
Forpointsources:
λ
fλ
Angularresolu8on
sin Θ = 1.22
or Δl = 1.22
D
D
(givenbytheRayleighcriterion)
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TelescopeFoci–wheretoputtheinstruments
Primefocus–widefield,fastbeambutdifficultto
accessandnotsuitableforheavyinstruments
Cassegrainfocus–moveswithtelescopes,small
field
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TelescopeFoci–wheretoputinstruments(2)
Nasmyth–idealforheavyinstrumentsto
putonastableplarorm,butfieldrotates
Coudé–veryslowbeam,usuallyforlarge
spectrographsinthe“basement”
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GrowthofTelescopeCollec@ngArea
sin Θ = 1.22
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λ
D
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MassLimita@ons
biggermirrorsrequire
•  thinner/segmentedmirrors
•  ac8vesupport
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Segmented,ThinandHoneycombMirrors
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Ac@veMirrorSupport
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Op@calTelescopesinComparison
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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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RadioTelescopes
Arecibo, Puerto Rico – the largest
Dishes similar to optical telescopes (305m) single-aperture telescope
but with much lower surface accuracy
Effelsberg, Germany –
100m fully steerable
telescope
Greenbank, USA – after
structural collapse (now rebuilt)
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ArraysandInterferometers
VLA in New Mexico – 27 antennae
(each 25m) in a Y-shape (up to 36 km
baseline)
WSRT (Westerbork) in
Drenthe – 14 antennae
along
2.7 km line
ALMA in Chile – 50 dishes (12m each) at
5000m altitude
400µm – 3mm (720 GHz – 84GHz)
LOFAR in the Netherlands
•  LOwFrequencyARrayusestwotypesoflowArecibo
costantennae:
• LowBandAntenna(10-90MHz)
• HighBandAntenna(110-250MHz).
•  Antennaeareorganizedin36sta8ons
•  over~100km.Eachsta8oncontains
•  96LBAsand48HBAs
•  Baselines:100m–1500km
•  MainLOFARsubsystems:
• sensorfields
• wideareanetworks
• centralprocessing
systems
• userinterfaces
X-rayTelescopes
• X-raysimpingingperpendicularonanymaterialarelargelyabsorbed
ratherthanreflected
• telescopeop8csbasedonglancinganglereflec8on(ratherthan
refrac8onorlargeanglereflec8on)
• typicalreflec8ngmaterialsforX-raymirrorsaregoldandiridium
(goldhasacri8calreflec8onangleof3.7degat1keV).
Gamma-RayTelescopes
FERMI satellite
Fig. 1 in arxiv.org/pdf/0902.1089v1.pdf
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MAGIC Cerenkov telescopes
magic.mpp.mpg.de/newcomers/introduction/
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RHESSIGamma-Ray
hesperia.gsfc.nasa.gov/rhessi3/
mission
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NeutrinoTelescopes
neutrino.kek.jp/figures.html
Super-Kamiokande, 50,000 tons of water
15-2-2016
www.sno.phy.queensu.ca/sno/
images
Sudbury Neutrino Observatory,
1000 tons of D2O
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NeutrinoDetec@on
•  scaxeringofneutrinos
onelectrons:e-+νeè
e-+νe
•  electronacceleratedto
v>cèCerenkov
radia8on
•  solarneutrinos
•  neutrinooscilla8ons
•  neutrinosfrom
SN1987A
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NeutrinosinIceandWater
gallery.icecube.wisc.edu
IceCube at the South Pole
15-2-2016
antares.in2p3.fr/Gallery
ANTARES in Mediterranean Sea
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Gravita@onalWaveDetectors
ligo.org/multimedia/gallery
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GWMeasurementPrinciple
ligo.org/science/GW-Overview/images/IFO.jpg
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