diff --git a/shared/src/constants.ts b/shared/src/constants.ts
index 75e7f27..45a7dd4 100644
--- a/shared/src/constants.ts
+++ b/shared/src/constants.ts
@@ -16,6 +16,15 @@ export const HUNGER_THRESHOLD = 30;
 export const ENERGY_THRESHOLD = 20;
 export const NEED_RECOVERY_RATE = 0.5;
 
+// Day/night cycle
+export const DAY_NIGHT_RATIO = 2;           // day is 2x as long as night
+export const DAY_HOURS = 12;                // game hours of daytime
+export const NIGHT_HOURS = DAY_HOURS / DAY_NIGHT_RATIO; // 6 hours of night
+export const TOTAL_HOURS = DAY_HOURS + NIGHT_HOURS;     // 18 hours total cycle
+export const SUNSET_DURATION_HOURS = 1;     // game hours for sunset transition
+export const SUNRISE_DURATION_HOURS = 1;    // game hours for sunrise transition
+export const NIGHT_DARKNESS = 0.3;          // max overlay opacity (0-1)
+
 // Directions (row index in spritesheet)
 export const Direction = {
   DOWN: 0,