Luminosity and brightness

Question 1

What does it mean is something is luminous?

Answer 1

It is actively emitting visible light.

E.g a light bulb or a star

Question 2

What is luminosity?

Answer 2

Total amount of radiant energy emitted per second, or its power

L= energy (J)/ time (s)
(Js^-2 or Watts (W))

Question 3

What is L0, and what is it used for?

Answer 3

The sun’s luminous output is used as a reference to measure the output of other stars.

Question 4

What is brightness of a star?

Answer 4

How bright we perceive it to be from earth.

Question 5

What two things does brightness depend on?

Answer 5

Luminosity and distance

Question 6

How is brightness measured?

Answer 6

W/m^2 or Lumens (Lux)

Question 7

What can be brightness also be classified as, and what does this describe?

Answer 7

Intensity
This describes luminosity per unit area.

Question 8

What is the relationship between intensity and distance of an object?

Answer 8

Inverse proportions

I = 1/d^2

Question 9

What is a Cepheid star, and how are its properties linked to the star’s luminosity?

Answer 9

A star that pulsates, the period of pulsation is related to the star’s luminosity