diff --git a/common/src/mayan.test.ts b/common/src/mayan.test.ts
index a1ffe15..be77451 100644
--- a/common/src/mayan.test.ts
+++ b/common/src/mayan.test.ts
@@ -1,4 +1,4 @@
-import {formatHaab, formatTzolkin, jdnHaab, jdnTzolkin, TzolkinName, tzolkinName} from './mayan';
+import {formatHaab, formatLordOfNight, formatTzolkin, jdnHaab, jdnTzolkin, TzolkinName, tzolkinName} from './mayan';
 
 describe('tzolkinName', () => {
     it('should return correct name for IMIX', () => {
@@ -153,3 +153,41 @@ describe('jdnHaab', () => {
         expect(jdnHaab(-1)).toEqual({month: 4, day: 4});
     });
 });
+
+describe('formatLordOfNight', () => {
+    it('should format Lord of Night 1', () => {
+        expect(formatLordOfNight(1)).toBe('G1');
+    });
+
+    it('should format Lord of Night 2', () => {
+        expect(formatLordOfNight(2)).toBe('G2');
+    });
+
+    it('should format Lord of Night 3', () => {
+        expect(formatLordOfNight(3)).toBe('G3');
+    });
+
+    it('should format Lord of Night 4', () => {
+        expect(formatLordOfNight(4)).toBe('G4');
+    });
+
+    it('should format Lord of Night 5', () => {
+        expect(formatLordOfNight(5)).toBe('G5');
+    });
+
+    it('should format Lord of Night 6', () => {
+        expect(formatLordOfNight(6)).toBe('G6');
+    });
+
+    it('should format Lord of Night 7', () => {
+        expect(formatLordOfNight(7)).toBe('G7');
+    });
+
+    it('should format Lord of Night 8', () => {
+        expect(formatLordOfNight(8)).toBe('G8');
+    });
+
+    it('should format Lord of Night 9', () => {
+        expect(formatLordOfNight(9)).toBe('G9');
+    });
+});
diff --git a/common/src/mayan.ts b/common/src/mayan.ts
index 1db5cb4..e9a5107 100644
--- a/common/src/mayan.ts
+++ b/common/src/mayan.ts
@@ -107,3 +107,9 @@ export function jdnHaab(jdn: number): Haab {
         day: yearDay % 20 as HaabDay,
     };
 }
+
+export type LordOfNight = 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9;
+
+export function formatLordOfNight(lordOfNight: LordOfNight): string {
+    return `G${lordOfNight}`;
+}