diff --git a/src/nature.rs b/src/nature.rs
index 6b47701..fa35ab1 100644
--- a/src/nature.rs
+++ b/src/nature.rs
@@ -163,6 +163,7 @@ pub fn inverse_lorentz_factor_custom_c(speed: f64, c: f64) -> f64 {
     (1.0 - (speed.powf(2.0) / c.powf(2.0))).sqrt()
 }
 
+/// Calculates orbit duration in seconds, with given parameters, assuming circular orbit.
 pub fn simple_orbital_period(mass: f64, distance: f64) -> f64 {
     return 2.0 * PI * (distance.powf(3.0) / (G * mass)).sqrt();
 }