Observational techniques... coordinates, RA intro

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Coordinate Systems Alt, El, Az, Zenith Angle
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Coordinate Systems Alt, El, Az, Zenith Angle
Azimuth
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Celestial Sphere
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Coordinates on Celestial Sphere
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One hemisphere view from inside
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Map from inside of Cel. Sphere, looking out
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Map from inside of Celestial Sphere of radio
sky
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Zero of R.A. coordinate system tied to
intersection of Ecliptic Plane with Equatorial
Plane
The Vernal Equinox
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Moons orbit inclined 5 deg w.r.t. plane of
ecliptic
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after 4.65 (18.6/4) years, .
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after 9.3 years,
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after 18.6 years Moon orbit has regressed full
turn
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Vernal Equinox
RA0
N.P.
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Dec
RA
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HA Hour Angle
HA
RA
Vernal Equinox
N.P.
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RA
Vernal Equinox
N.P.
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Sun
Vernal Equinox
RA0
N.P.
Solar Time hours since midnight
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Sun
Greenwich
Vernal Equinox
RA0
N.P.
Greenwich Time . becomes UTC Coordinated
Universal Time
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6 hours
Local Siderial Time LST
Vernal Equinox
RA0
12 hours
N.P.
18 hours
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One hemisphere future North Poles
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Zero of R.A. coordinate system tied to
intersection of Ecliptic Plane with Equatorial
Plane
The Vernal Equinox
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motion of RA0, Decl0 (J2000) in past and
future Epochs Current epoch called epoch of
date
(at equator, 4 minutes of time 1 degrees)
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Spherical Trigonometry Spherical
triangles sides are portions of great
circles
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PCD is a spherical triangle PAB is NOT a
spherical triangle
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c
A
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Spherical triangles
sin A sin B sin C sin a sin b sin c


cos c cos a cos b sin a sin b cos C
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Radio Astronomy Overview
Radio source

• Goals of telescope
• maximize collection of energy (sensitivity or
  gain)
• isolate source emission from other sources
  (directional gain dynamic range)

Collecting area
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LOFAR elements
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thought experiment
2 wires out
(antennas are reciprocal devices can
receive or broadcast)
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thought experiment
Black Body oven at temperature T
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thought experiment

R
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thought experiment
wait a while reach equilibrium at T

R
warm resistor delivers power P kT B (B
frequency bandwidth k Boltzmann Const)
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real definition
Measure Antenna output Power as Ta antenna
temperature
Ta
temp T
warm resistor produces P kT B Pa kTa B
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Radio source
Reception Pattern or Power Pattern
Collecting area
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Radio source
If source with brightness temperature Tb
fills the beam (reception pattern), then Ta
Tb
Collecting area
(!! No dependence on telescope if emission fills
beam !!)
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receiver temperature
quantify Receiver internal noise Power as Tr
receiver temperature
Ta
Ampl, etc
Real electronics adds noise
treat as ideal, noise-free amp with added power
from warm R
TrTa
Ampl, etc
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system temperature
quantify total receiver System noise power as
Tsys
TsysTa
Ampl, etc
RMS fluctuations DT DT
(fac)Tsys/(B tint)1/2
Fac 1 2 B Bandwidth, Hz tint integration
time, seconds
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Radio point source
Power collected Sn Aeff B/2 Sn flux density
(watts/sq-m/Hz) 1 Jansky 1 Jy 10-26
w/sq-m/Hz Aeff effective area (sq-m) B
frequency bandwith (Hz) Ta Sn Aeff /2k
Collecting area