diff --git a/Scripts/check-moon-phase.ps1 b/Scripts/check-moon-phase.ps1
index a530a6ae..1cc0fc4b 100644
--- a/Scripts/check-moon-phase.ps1
+++ b/Scripts/check-moon-phase.ps1
@@ -12,7 +12,7 @@
 #>
 
 try {
-	$LunarCycle = 29.53058770576 # in days
+	$LunarCycle = 29.53058868 # synodic period in days, time between successive new moons
 	$LunarHalfCycle = $LunarCycle / 2.0
 	$Phases = @("New moon", "Waxing crescent moon", "First quarter moon", "Waxing gibbous moon", "Full moon", "Waning gibbous moon", "Last quarter moon", "Waning crescent moon")
 	$PhaseLength = $LunarCycle / 8.0