diff --git a/README.md b/README.md
index 2a78abb..20feedc 100644
--- a/README.md
+++ b/README.md
@@ -47,7 +47,7 @@ HenonHeiles.py:
 	Standalone Henon-Heiles model.
 
 Hill.py: 
-	Hill potentials for 3-body problem.
+	Hill potentials for 3-body problem.  (See: https://galileo-unbound.blog/2019/07/19/getting-armstrong-aldrin-and-collins-home-from-the-moon-apollo-11-and-the-three-body-problem/)
 
 Kuramoto.py: 
 	Kuramoto synchronization of phase oscillators on a complete graph.