![Page 1: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/1.jpg)
Introduction toRadio Astronomy
Greg Hallenbeck2016 UAT Workshop @ Green Bank
![Page 2: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/2.jpg)
Outline
Sources of Radio EmissionContinuum Sources versus Spectral LinesThe HI Line
Details of the HI LineWhat is our data like?What can we learn from each source?
The Radio TelescopeHow do we actually detect this stuff?How do we get from the sky to the data?
![Page 3: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/3.jpg)
I. Radio Emission Sources
![Page 4: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/4.jpg)
← Optical Light →
The Electromagnetic Spectrum
Radio
![Page 5: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/5.jpg)
A Galaxy Spectrum (Apologies to the radio astronomers)
Continuum EmissionRadiation at a wide range of wavelengths❖ Thermal Emission❖ Bremsstrahlung (aka free-free)❖ Synchrotron❖ Inverse Compton Scattering
Spectral LineRadiation at a wide range of wavelengths❖ The HI Line
![Page 6: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/6.jpg)
Categories of Emission
Continuum Emission — “The Background”Radiation at a wide range of wavelengths❖ Thermal Emission❖ Synchrotron❖ Bremsstrahlung (aka free-free)❖ Inverse Compton Scattering
Spectral Lines — “The Spikes”Radiation at specific wavelengths❖ The HI Line❖ Pretty much any element or molecule has lines.
![Page 7: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/7.jpg)
Thermal Emission
Hot Things GlowEmit radiation at all wavelengths
The peak of emission depends on THigher T → shorter wavelength
Regulus (12,000 K)Peak is 250 nm
The Sun (6,000 K)Peak is 500 nm
Jupiter (100 K)Peak is 30 µm
![Page 8: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/8.jpg)
Thermal Emission
How cold corresponds to a radio peak?A 3 K source has peak at 1 mm.Not getting any colder than that.
![Page 9: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/9.jpg)
Synchrotron Radiation
Magnetic FieldsMake charged particles move in circles.Accelerating charges radiate.
Synchrotron IngredientsStrong magnetic fieldsHigh energies, ionized particles.
Found in jets:❖ Active galactic nuclei❖ Quasars❖ Protoplanetary disks
![Page 10: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/10.jpg)
Synchrotron Radiation
Jets from a ProtostarAt right: an optical image.Half of jet is obscured by dust cloud
But radio can go right through dust...
![Page 11: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/11.jpg)
Synchrotron Radiation
Jets from a ProtostarAt right: an optical image.Half of jet is obscured by dust cloud
But radio can go right through dust...
![Page 12: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/12.jpg)
Jets from Cygnus AAt right: VLA imageThe optical counterpart to the galaxy is tiny
Synchrotron Radiation
![Page 13: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/13.jpg)
The Hydrogen Atom
e-p+
For Archaic Reasons:H I Atomic “Neutral” HydrogenH II Ionized H+
![Page 14: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/14.jpg)
The Hydrogen Atom
n = 1; E = -13.6 eV Ground State
n = 2; E = -3.4 eV
n = 3; E = -1.5 eVDiscrete Energy LevelsTransitions due either to emission or absorption of photons.
n = 4; E = -0.9 eV
ep
![Page 15: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/15.jpg)
The Hydrogen Atom
n = 1; E = -13.6 eV Ground State
n = 2; E = -3.4 eV
n = 3; E = -1.5 eVDiscrete Energy LevelsTransitions due either to emission or absorption of photons.
nf = 1: Ultraviolet LightLowest Energy: 10.2 eV (121 nm)Most Hydrogen sits at n = 1!Hydrogen doesn’t emit much light.
n = 4; E = -0.9 eV
![Page 16: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/16.jpg)
The Hydrogen Atom
n = 1; E = -13.6 eV Ground State
n = 2; E = -3.4 eV
n = 3; E = -1.5 eVDiscrete Energy LevelsTransitions due either to emission or absorption of photons.
nf = 1: Ultraviolet LightLowest Energy: 10.2 eV (121 nm)Most Hydrogen sits at n = 1!Hydrogen doesn’t emit much light.
nf = 2: Visible LightRed (656 nm; Hα),Blue (486 nm; Hβ),Violet (434 nm; Hγ),
and so on for ni ≥ 4(the rest are all UV)
n = 4; E = -0.9 eV
![Page 17: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/17.jpg)
The HI Radio Line
n = 1; E = -13.6 eV
n = 2; E = -3.4 eV
n = 3; E = -1.5 eVn = 4; E = -0.9 eVUsed to Observe HI
Frequency: 1420 MHzWavelength: 21 cm
Energy: 6×10-6 eV
![Page 18: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/18.jpg)
The HI Radio Line
n = 1; E = -13.6 eV
n = 2; E = -3.4 eV
n = 3; E = -1.5 eVn = 4; E = -0.9 eVUsed to Observe HI
Frequency: 1420 MHzWavelength: 21 cm
Energy: 6×10-6 eV ???
![Page 19: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/19.jpg)
Proton and Electron Carry Angular Momentum
Specifically, Spin Angular MomentumAs if they were rapidly rotating objects.(but electrons are likely of zero radius, so not quite)
The Hydrogen Atom, Revisited
![Page 20: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/20.jpg)
Different Energies Depending on Alignment:
Slightly Higher Energy
Slightly Lower Energy
The Energy Difference is 6×10-6 eV (or λ = 21 cm).
The Hydrogen Atom, Revisited
![Page 21: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/21.jpg)
Why Are the Spin States Different Energies?
Slightly Higher Energy
Slightly Lower Energy
Spin + Charge = Magnetic MomentDifferent energies come from the alignment or misalignment of the magnets.
Shenanigans
![Page 22: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/22.jpg)
Excitation Temperature is 0.07 K (T = E/kB)
So the actual temperature of the H doesn’t matter.i.e. hydrogen is always* excited
State Lifetime is 107 yrs.Need a ton** of Hydrogen to observe it.
Unlikely to be Absorbed En RouteTotal Energy from line directly proportional to mass.
*okay fine, half of it is always excited.**well, a few solar masses.
Properties of the HI Line
![Page 23: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/23.jpg)
The HI Line
![Page 24: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/24.jpg)
II. Details of the HI Line
![Page 25: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/25.jpg)
The HI Line
When Observed, the Line Looks Like This:
Features:Centered at 1420 MHzAll Emission is at Single FeatureLine Has No Interesting Features; Nice Sharp Spike.
Frequency (MHz)1420 MHz
![Page 26: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/26.jpg)
The HI Line
When Observed, the Line Looks Like This:
Features:Centered at 1420 MHzAll Emission is at Single FeatureLine Has No Interesting Features; Nice Sharp Spike.
![Page 27: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/27.jpg)
The HI Line
When Observed, the Line Looks Like This:
Features:Centered at 1420 MHzAll Emission is at Single FeatureLine Has No Interesting Features; Nice Sharp Spike.
![Page 28: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/28.jpg)
Doppler Shift
Galaxies are (usually) move away from us.All of lines are redshiftedKnow Rest frequency (1420 MHz), Can Find Velocity
Velocity (km/s)Vhelio
![Page 29: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/29.jpg)
Galaxies Rotate:● Half of galaxy is approaching us.● Half of galaxy is moving away from us.● (Relative to overall motion away)
Doppler Shift within galaxy broadens line.Rotation nearly constant across galaxy → “horns”
Galaxy Rotation
Velocity (km/s)Vhelio
W50
![Page 30: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/30.jpg)
Galaxies Have Different Masses of HIMore HI, Stronger HI Line(for a given distance from Earth)
Convert Area to Mass:
Hydrogen Mass
Velocity (km/s)Vhelio
W50
Integrated Flux Density
![Page 31: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/31.jpg)
Vhelio (Position of Line)How Fast is the Galaxy Moving?How Far is it from Earth?
W50 (Line Width)How Fast is it Rotating?What are its Internal Kinematics Like?
Integrated Flux (Area Under Curve)How much HI is in It?
Recap: Features of HI Line
Velocity (km/s)Vhelio
W50
Integrated Flux Density
![Page 32: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/32.jpg)
III. The Radio Telescope
![Page 33: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/33.jpg)
Basic Principles
Incoming Radio Waves
Receiv
er
![Page 34: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/34.jpg)
The DishCollects incoming light, focuses at receiver.Light then converted to electronic signals
Effects of Dish SizeLarger area → More sensitive
Larger diameter → better resolution(Unlike optical telescopes)
Schematic
![Page 35: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/35.jpg)
The telescope for the SDSS is 2.5 m ( ≈ 500 nm)Arecibo is 300 m ( ≈ 21 cm)
Telescope ResolutionWavelength
D Telescope Diameter
→ SDSS Resolution is 3500× better!
Dish Size and Resolution
SDSS Optical Image
ALFALFA HI Map
![Page 36: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/36.jpg)
ReceiverConvert radio wave to electric signal
AmplifierRadio signals are extremely weak.
DownconverterConverts signal to a lower frequency.
Another Amplifier
SpectrometerTurns signal into a spectrum.
Signal Path: From Receiver to You
Seven Feeds on the ALFA Receiver at Arecibo
Cross-Section of a190 GHz feedhorn
![Page 37: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/37.jpg)
InterferenceIf ~ hole size, waves taking differentpaths “interfere” leaving pattern onfar screen.
Effect on TelescopeFor radio, ~ 10 cmClose to sizes of aperture.Bright spot on sky is not a “spot”.
Additional “ripples” = side lobes
(No problem for optical ~ 500 nm telescopes)
What Does the Receiver See?
![Page 38: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/38.jpg)
Arecibo’s ALFA has seven beams packed close together.
What Does the Receiver See?
![Page 39: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/39.jpg)
Optical TelescopesRange in from 500 nm - 1000 nm (factor of ×2)Use same receiver, electronics, etc.
Radio TelescopeRange in from 1 cm - 1 m (factor of ×100)Different wavelengths need different receivers.
❖ Need a smart way to reuse electronics.❖ Electronics to at MHz frequencies more convenient than GHz-THz.
Solution:Mix signal with a fixed frequency, the local oscillator.
The Downconverter
![Page 40: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/40.jpg)
The Downconverter
Frequency
Inte
nsity
Low Frequencies(Convenient for
Electronic Design)
Actual Signal(Too High Frequency)
![Page 41: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/41.jpg)
The Downconverter
Frequency
Inte
nsity
Low Frequencies(Convenient for
Electronic Design)
Actual Signal(Too High Frequency)
Local Oscillator(Frequency Chosen for
this Observation)
![Page 42: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/42.jpg)
We add together the signal and the LO:
Trig Identity: cos(fsig) + cos(flo) = 2 × cos(fsig + flo) × cos(fsig - flo)
The Downconverter Signal and LO have almost same frequency
Slowly varying signal (keep)Rapidly varying signal (ignore)
![Page 43: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/43.jpg)
The Downconverter
Frequency
Inte
nsity
Actual Signal(Too High Frequency)
Local Oscillator(Frequency Chosen for
this Observation)
Low Frequency Converted Signal
![Page 44: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/44.jpg)
Convert signal in “time space” to spectrumin “frequency space”
Optical EquivalentUse a prism, grism, or albumcover of dark side of the Moon.
Radio AstronomySpectrometer performs Fourier Transformof electronic signal.
Signal is then saved to disk.
The Spectrometer
![Page 45: Radio Astronomy Introduction to - Cornell Universityegg.astro.cornell.edu › alfalfa › ugradteam › uat16talks › ... · Introduction to Radio Astronomy Greg Hallenbeck 2016](https://reader034.vdocuments.mx/reader034/viewer/2022042408/5f233b7d51f219408c1880e4/html5/thumbnails/45.jpg)
End of Talk.</mic>