Introduction to Radio Astronomy

Question 1

Photon counting is

Answer 1

Not an option in radio astronomy

Question 2

Spectral Flux Density can be represented by and measured in

Answer 2

S and measured in J s^-1 m^-2 Hz^-1

Question 3

Since photon counting is not an option we can think

Answer 3

Classically in terms of waves, electric fields etc..

Question 4

1 Jansky (Jy) =

Answer 4

10^-26 Js^-1 m^-2 Hz-^1

Question 5

power out =

Answer 5

S A Δv which is measured in Js^-1

Question 6

Extended objects (i.e. not a point source) have both

Answer 6

Flux Density, S , and a Flux Density Per Steradian, I₀

Question 7

Specific Intensity/Spectral Intensity/Sky Brightness/Surface Brightness are represented by the symbol and can be measured in

Answer 7

represented by the symbol Iᵥ or B and is measured in Js^-1 m^-2 Hz^-1 sr^-1

Question 8

B =

Answer 8

S / Ω

or more generally

∫ B (θ,ϕ) dΩ

for small angles

Question 9

measured surface brightness of an object does not depend on

Answer 9

its distance away

Question 10

hv &laquo_space;kT when

Answer 10

observing a black body source

exp (hv/kT) ≈ 1 + hv/kT

Question 11

Rayleigh-Jeans Law

Answer 11

B(v) ≈ 2kTv² / c²

Question 12

more generally, we can work with the temperature distribution over the sky T(θ,ϕ)

therefore S =

Answer 12

S = 2kv² / c² ∫ T (θ,ϕ) dΩ

S = 2k / λ² ∫ T (θ,ϕ) dΩ

Question 13

Most radio sources do NOT emit via

Answer 13

a thermal blackbody mechanism

Question 14

you can define an effective temperature or brightness temperature Tb

Tb =

Answer 14

Tb = c² / 2kv² * B

Question 15

Tb = T only if

Answer 15

The object is a blackbody

T&raquo_space; hv/k

Question 16

System Temperature definition

Answer 16

way of characterizing the amount of noise inherent in a radio telescopes.

Question 17

for v > 50GHz

Answer 17

Tsys&raquo_space; Ta

Question 18

for v < 300MHz

Answer 18

Ta dominates