# Spherical coordinate system

The three coordinate variables are ${\displaystyle r,\theta ,{\text{ and }}\varphi }$
The two angular numbers are related to lines of longitude and latitude on Earth. Earth's longitude is the same as the variable phi, which can be written as either ${\displaystyle \phi }$ or ${\displaystyle \varphi \!.}$ The latitude resembles the variable ${\displaystyle \theta \,\!}$ (theta), except that some authors define ${\displaystyle \theta =0}$ to be at the north pole instead of at the equator.