We can also apply the Stefan-Boltzmann Law : (where r = radius of the star)
AND the Inverse Square Law : (here D = distance to the star)




Knowing these relationships, we can say something about the Radius (r), Temperature (T), or Distance (D) to a star. For example:

Two stars A & B are known to be the same Temperature and Distance.
Star A is brighter (has a greater Flux as seen from Earth) than Star B.

Which is smaller?         How do you know this?







Two stars A & B are known to be the same Temperature and Radius.
Star A is brighter(has a greater Flux as seen from Earth) than Star B.

Which is further?         How do you know this?







Two stars A & B are known to have the same Radius and Distance.
Star A is brighter (has a greater Flux as seen from Earth) than Star B.

Which is hotter?         How do you know this?