Transcript Introduction to Radio Astronomy

Crab Nebula & Pulsar
Introduction to
Radio Astronomy
Jeremy Waller
Jodrell Bank Telescope
100” Hooker Telescope
Astronomy
Ptolemy
Road Map
Tycho Brahe
S&T
Bayer
Flamsteed
Refracting
Telescope
Keppler
Galileo
Newton
Communications
S&T
Argelander
Siedel
Abbe
Schott
Gauss
Maxwell
Hertz
WW2
Reflecting
Telescope
Jansky
Reber
Antennas
Aka: Radio Telescopes
Wiener
Radio
Visual
Kolmogoroff
Sky Map
Satellite
Comms.
Adaptive Optics
Interferometers
VLA
Pulsars
Quasars
Radio Galaxies
Planets
Stars
Sun
DSP
Statistical
Communications
Brief History of Communications
Properties of Electromagnetic Radiation
-What is Electromagnetic Radiation?
-Frequency and Wavelength
-Inverse-Square Law of Propagation
-Electromagnetic Spectrum
Causes of Electromagnetic Emissions
-Blackbody Characteristics
-Thermal Radiation
-Continuum Emissions
(eg. Planetry Nebulae, Galactic nuclei, Comets)
-Line Spectra Emission … Atoms and Molecules
-Other sources
Synchrotron Radiation
Representative Sources of RF
-Star
-Pulsar
-Jupiter
The Radio Telescope
Sources of RF:
Stars:
-Variable Stars
-Pulsars
-Sun
Galactic and Extragalactic Sources:
-Quasars
Planetary:
-Jupiter System
-Moon
-Comets
Sources of Interference:
-Sun
-Lightning
-Ionosphere
-Power grid, transformers, distribution
- Radars- military and others
-Radio and TV transmitters
-Satellite transmitters
-Mobile phones
History of Communications
1800 – 1837
Volta discovers the battery
Mathematics – Laplace, Fourier, Cauchy
Oersted, Ampere, Faraday, Henry, Ohms Law (1826)
Early Telegraph Systems (Gauss & Weber) (Wheatstone & Cooke)
1838 – 1866
Birth of Telegraphy – Transatlantic cable (1866)
Pulse Response of a cable calculated(1855) – Lord Kelvin.
1864
A Dynamical Theory of the Electromagnetic Field”
J.C.Maxwell – Predicts EM Radiation
1876 – 1899
The Birth of Telephony
Stowger devises the step by step switch.
1887-1907
Hertz verifies Maxwells theory
1904-1920
Electronics Applied to Radio and Telephone
1920-1928
Papers by Nyquist, Carson, Hartley
History of Communications – cont.
1923-1938
Birth of Television
1939-1945 – WW2
Radar and Microwave Systems developed
Wiener and Kolmogoroff – Statistical Signal Detection
1948
A Mathematical Theory of Communication
Claude Shannon.
.
.
.
EM wave Propagates as a series
Of Electric and Magnetic fields

E field
cw
ccw
Notice:
Electric field is closed - does not
terminate on a charge.
H field

c
f
“ Front View ”
E
H
Field variation with time
Polarisation – Direction of E field Vector
Linear
-Vertical, Horizontal or other angle
Elliptical
- Circular
-RH or LH
Property of the Radiated Energy
3m
9
2m
4
1m
1
Isotropic
Radiator
Inverse Square Law
-Power per unit area
falls as the square of
the distance from the
source
-Doubling the distance
reduces the power per
square metre by x4
Effects on RF Emissions
Earths Atmosphere
-Atmospheric “Windows”
-Absorption and Emission Lines
-Reflection
-Refraction
-Phase
-Scintillation
-Faraday Rotation
Source Motion & Gravity
-Doppler Effect
-Gravitational Red Shifting
-Gravitational Lensing
-Occultations
Atmospheric Absorption
Spacecraft
Absorption
100%
Radio
Telescopes
0%
0.01nm
0.1nm
1nm
10 nm
100 nm
1m
10m
100m
1mm
4.54 mm
… 66GHz.
10 mm 100 mm
1m
10 m
100 m
Karl Jansky (engineer)
Bell Telephone Laboratories
- 1931`
- Identifying sources of interference
with radio telephone service.
- Rotatable Antenna tuned to 20.5 MHz
-Diameter … 100 ft (30 m).
-Height … 20 ft (6 m)
Three types of static:
-Nearby thunderstorms
-Distant thunderstorms,
-Faint hiss of unknown origin.
- Period  23 hours : 56 minutes.
Comparing the above observations with optical astronomical maps
Conclusion:
-The radiation (Hiss) was coming from the Milky Way
-Peaked in the direction of the centre of the galaxy,
in the constellation of Sagittarius.
Grote Reber
-Pioneer of Radio Astronomy
-9 m Paraboloidal
antenna (1937)
… Radio Telescope
-Repeats Jansky’s work
-Conducts the first sky survey
in the radio frequencies.
Pulsars as an example
Jocelyn Bell
Discovers the Pulsar in 1967
RadioTelescope:
-2000 dipoles
-4.5 acres and
-Operational in July 1967
-Aperture Synthesis
Strong Radio Sources:
(Radiance … Jansky)
10 MHz
Cassiopeia A 100000
Cygnus A
70000
Sagittarius A
Centaurus A
Virgo A
10000
Taurus A
100 MHz
1 GHz 10 GHz
19500
13800
4000
3000
1800
1700
3300
2340
2000
2000
250
955
1000
300
100
Supernova remnant
Radio galaxy
Center of our galaxy
Peculiar galaxy
M87, galaxy with "jet"
M1 - Crab Nebula - SN
remnant
Sun, quiet
Sun, disturbed
100 10 000 100 000
1E+7 1E+8 1E+8
1E+6
1E+8
Moon
0.1
3
50
10000
Jupiter
1E+7
0
0
50
1E+6
3E+5
Sky background 2E+7
3E+6
Source: "Radio Astronomy" by Kraus, McGraw-Hill 1966
Milky Way in Various Wavelengths:
Radio
Infra-Red
Visible
X-Ray
From Griffith Observatory and JPL),
Radio View of the Milky Way
Radio continuum emission Example
(Staff Research at AAT)
Gamma Velorum
- Nearest and brightest Wolf Rayet star
-Binary system with an O-star
companion and an orbital period of 79 days.
-Radio Continuum RF @ 10 GHz (3 cm)
-30 mJansky
Observation
RF is non-thermal in origin and
arises from shock fronts which form as the stellar wind
from the Wolf Rayet star collides with the stellar wind of
the O-star.
Monitoring continuum RF at 3, 6, 13 and 20 cm over a three-month
period. Initial results indicate that radio variability is indeed present.
Pulsar as an example
Tutorial on Pulsars – Jodrell Bank
-http://www.jb.man.ac.uk/~pulsar/Education/Tutorial/tut/tut.htm
-Duty cycle ~ 5%
-Some Individual pulses very variable in intensity
-Stable profile if several hundred pulses added
-Strongly linearly polarised
-Monotonic polarisation position angle swing through
the pulse implies the origin is near a magnetic pole
-Very high brightness temperature implies coherent emission
-Drifting subpulses
-Mode changing
The lighthouse model of a radio pulsar:
A rapidly central neutron
star with a strong magnetic field,
inclined to the rotation axis with
radio emission emanating from the magnetic poles
The lighthouse model of a radio pulsar:
Wobble in the spin axis
Radio Emissions From Jupiter
Bernard Burke and Kenneth Franklin
of the Carnegie Institution in Washington D.C.
discovered that the planet Jupiter was a strong source of radio waves.
One arm of Mills Cross Array (circa 1954)
Radio Emissions From Jupiter
-Synchrotron radiation between 70MHz to over 20 GHz
- At < 40 MHz the planet’s radio emission
is dominated by emissions many orders stronger
than the synchrotron radiation.
-1E+7 J @ 10 MHz.
-Known causes
-Planetary rotation modulation,
-Modulation by Io and/or its torus,
-Influence by the solar wind.
Significant number of radio variations
are not currently explained by any known mechanism.
Prime Focus
The Radio Telescope:
-Antenna
-Single Antenna
-Array Antenna
Feed
-Receiver
-Low Noise front end
-Signal Processing
-Depends on what
one wants done !!
Casagrain
Feed
Secondary
Reflector
Paraboloidal Reflector
Antenna Array
The Radio Telescope
-Will be quite Large
-Need extremely high Resolution at the longer wavelengths
-Looking for very weak signals
-Very distant sources
-Emissions may be weak (eg. Gamma Velorum)
-eg Continuum emissions
Signal Processing System
Antenna & Receiver Array
-Experiment (?)
-Beam Forming
-Aperture synthesis
-Signal Enhancement and Detection
-Signal Properties
-Signal Strength (t)
-RF Doppler
-Polarisation
-Image forming
R 21
R 11
R 22
R 01
R 12
R 23
R 02
R 13
R 03
Receiver Channel #1
ADC
Low Noise Amp
Antenna
Control
Frequency
Translation
IF Amp
THE END
Any Questions ?
SETI
-Discussions at the Maid and Magpie
-Date? … TBD