How do Cepheid variables indicate distance? The length of these stars' pulsations is always related to their intrinsic brightness. Astronomers can use this knowledge to calculate distance.

Knowing pupillary distance is a requirement when people buy glasses. Learn what pupillary distance is and how to measure it alone or with another person's help.

This persnickety number determines the strength of magnetic fields. It figures in everything from motors and generators to ...