diff --git a/assets/js/utils.js b/assets/js/utils.js
index 9313683..15f3dab 100644
--- a/assets/js/utils.js
+++ b/assets/js/utils.js
@@ -267,7 +267,7 @@ export function confidenceBand(i) {
 export function moonPhaseFraction(date) {
   const JD = date.getTime() / 86400000 + 2440587.5;
   const syn = 29.530588;
-  const ref = 2451550.1;
+  const ref = 2451550.2597;
   let p = ((JD - ref) % syn) / syn;
   if (p < 0) p += 1;
   return p;