Quantifying Brightness, Fluxes, Luminosities & Magnitudes

Question 1

What is the flux? What are its units?

Answer 1

The received light power per unit area. [W m^-2]

Question 2

What is the intrinsic power at the source and its units?

Answer 2

Luminosity [W =Js^-1]

Question 3

How do you work out the luminosity from the flux?

Answer 3

If you have an imaginary sphere around the star and the flux is emitted the same in all direction, the luminosity is the closed integral of the flux times the change in area.

Question 4

What is the equation for flux in terms of luminosity?

Answer 4

f = L/(4pi*d^2)

Question 5

How much does the flux change if the magnitude changes by 5?

Answer 5

Difference in 5 magnitudes is equal to a difference in 100x the flux.

Question 6

What is the equation for magnitudes of object?

Answer 6

m1-m2 = 0.25*log(f1/f2)

Question 7

What is the magnitude of Vega?

Answer 7

0

Question 8

What is absolute magnitude?

Answer 8

The apparent magnitude of an object if it were at a distance of 10pc from the observer.

Question 9

What is the equation involving apparent and absolute magnitude?

Answer 9

m-M = 5*log(d/10pc), where m is apparent magnitude and M is absolute magnitude.