Which statement correctly describes variable stars?
A) Variable stars with shorter periods have lower luminosities, so they can be observed when they are farther away.
B) Variable stars with longer periods have lower luminosities, so they can only be observed when they are close.
C) Variable stars with longer periods have lower luminosities, so they can be observed when they are farther away.
D) Variable stars with shorter periods have lower luminosities, so they can only be observed when they are close.

The Period-Luminosity relationship tells us that luminosity increases with the period, and of course the more luminosity a star has the more far away they can be seen, so from this we know that:

A) False since lower luminosities can be observed when they are close.

B) False since longer periods means higher luminosities

C) False since lower luminosities can be observed when they are close.

D) True: Variable stars with shorter periods have lower luminosities, so they can only be observed when they are close.