Period-Luminosity Relation for Cepheids

• Measure how bright a variable star appears in the sky.

• Measure the period of the star's bright-dim-bright cycle.

• Use the period-luminosity relation to find how bright the star is absolutely.

• The difference between the star's apparent and absolute brightness is used to calculate the star's distance (from the inverse square law for the dimming of light).

back | next | index