# Geometry of Gregorian Telescope

Geometry of Gregorian Telescope

This Demonstration shows the principle of a telescope designed by the Scottish mathematician and astronomer James Gregory in the seventeenth century; it was first built in 1673 by Robert Hooke. The parameters and are the semiaxes of the ellipse, and the equation of the parabola in polar coordinates is The ellipse and parabola have a common focus.

a

b

r=p/(1-cos(ϕ))