Introduction to radio astronomy Flashcards

1
Q

optical and radio astronomy correspond to the two

A

electromagnetically transparent windows in the Earth’s atmosphere

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

optical wavelengths

A

0.4 to 0.8 microns

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

radio wavelengths

A

1mm to 30m

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

photon counting is not an option in radio astronomy so we can almost always think

A

classically in terms of waves and electric fields rather than photons

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

the transition to quanta occurs in

A

sub-mm wave radio astronomy

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

in radio astronomy we usually work in terms of

A

spectral flux density (usually just called flux)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

flux

A

symbol S
units Wm^-2Hz^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

1 jansky

A

10^-26 Wm^-2Hz^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

maximum power out=

A

S A delta v

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

flux density corresponds loosely to

A

apparent magnitude in optical astronomy, in the sense that it is a measure of the strength of the signal we see from the source, at Earth

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

extended sources

A

sources that do not appear as just a point on the sky

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

extended sources have both a

A

total flux density s(v) and a flux density per steradian B(v)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

B(v) is a function of

A

position (theta, thi) on the sky

a map of B(v) across the sky is an image of the source

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

B(v) is also known as

A

specific intensity
spectral intensity
sky brightness
surface brightness

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

units of B(v)

A

Wm^-2Hz^-1sr^-1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

over a small patch of sky, the intensity of a sky pixel of solid angle d omega giving a flux density dS is

A

B=dS/d omega

17
Q

total flux density is given by

A

S = integral of B(theta,thi) d omega

18
Q

a source of uniform intensity B and total solid angle omega has a total flux

19
Q

why does the measured surface brightness of an object not depend on its distance from the observer

A

B= delta S/ delta omega

both an inverse square so B is not a function of r

20
Q

usually in radio astronomy, hv«

A

kbT for a blackbody source

21
Q

rayleigh jeans law

A

exp(hv/kbt) = 1 + hv/kbT

B(v) = 1kbTv^2/c^2

22
Q

can think of a radio telescope as

A

mapping the temperature of the sky

23
Q

most radio sources do not emit via a thermal blackbody mechanism so

A

can’t assign a temperature to them

24
Q

brightness temperature or effective temperature

A

a blackbody at Tb would have the same surface brightness as the source at the frequency in question

25
Tb is the real thermodynamic temperature of the source if and only if
the object is a blackbody T>>hv/kb
26