General Relativity: An Introduction for Physicists · Problem 9.17
The Schwarzschild geometry — Hobson, Efstathiou & Lasenby
Physics · circular-photon-orbit-period
Problem
A photon moves in a circular orbit at r=3μ in the Schwarzschild geometry. Show that the period of the orbit as measured by a stationary observer at this radius is τ=6πμ/c. What is the period of the orbit as measured by a stationary observer at infinity?