# Time
The real-world time, date and moon phase affect gameplay. All are determined by your system clock. Technically it is possible to change the clock to get a desired moon phase or time, but this is considered cheating.

Contents

1 Moon phase and date
2 Time
3 Strategy
4 References

Moon phase and date
 On 20 July 2023, the moon is new. Be careful!
Just as in real life, the NetHack world goes through several phases of the moon. [1] These have an effect on gameplay.
The date is only checked when the game is started or restored; if you keep playing without saving, you'll continue to see the effects even after the relevant period has passed (or not see the effects even though it has been reached). NetHack divides the month into eight phases of three or four days each; thus the full and new moon will be reported for a rather longer time than your calendar might depict.
During a full moon:

Your base Luck is increased by one.[2] ("You are lucky! Full moon tonight.")
Werecreatures, especially at night, will usually be in their animal form.[3]
Dogs will howl at night when #chatted to.[4]
You have a chance of not being able to tame dogs at night; failed attempts will still pacify them, and you can try repeatedly.[5]
During a new moon:

You get the message "Be careful! New moon tonight."
Contrary to popular belief, Luck is not decreased.[6]
If a cockatrice uses its hissing attack and you have no lizard corpse, you will always start turning into stone, rather than having a 1-in-10 chance.[7]

The following information pertains to an upcoming version (NetHack 3.7.0). If this version is now released, please verify that it is still accurate, then update the page to incorporate this information.

Carrying a lizard corpse no longer negates the effect of a new moon on cockatrice hisses, as of commit 8a9dc00.
NetHack knows when it is Friday the 13th, and decreases your base Luck by one accordingly.[8] The game gives a warning message: "Watch out! Bad things can happen on Friday the 13th."
If Friday the 13th happens to be a full moon, the modifiers to base Luck will cancel each other out. Between 1995 and 2025, Friday the 13th has occurred or will occur during (NetHack's definition of) a new or full moon on the following days:

Date
Year
Phase

September 13
1996
new

February 13
1998
full

March 13
1998
full

August 13
1999
new

October 13
2000
full

June 13
2003
full

March 13
2009
full

Date
Year
Phase

June 13
2014
full

November 13
2015
new

January 13
2017
full

July 13
2018
new

September 13
2019
full

October 13
2023
new

June 13
2025
full

The NAO phase of moon page shows both the current phase of the moon and when it will next be full moon.

Time
Night is 22:00 - 05:59 (10:00pm - 5:59am) according to your local clock, or according to the server's clock if playing remotely. At night:

Your chance of changing into your animal form when you have lycanthropy is one in every 60 moves instead of once in every 80 moves.[9]
Gremlins can steal intrinsics.[10]
Werecreatures can summon more easily, and are more likely to be in their animal form, particularly when the moon is full.
Midnight is 0:00 - 0:59. At midnight:

Undead do twice as much damage.[11]
You get a different message when entering a graveyard. ("Run away! Run away!" instead of "You have an uncanny feeling...")[12]
Additionally, vampires can give different messages when #chatted to at night and midnight.

Strategy
While changing the system clock is most certainly cheating, you may prefer to stop playing at night when around hostile gremlins, or at midnight when clearing out a graveyard.

References

↑ hacklib.c in NetHack 3.4.3, line 564

↑ timeout.c in NetHack 3.4.3, line 166

↑ were.c in NetHack 3.4.3, line 18

↑ sounds.c in NetHack 3.4.3, line 546

↑ dog.c in NetHack 3.4.3, line 759

↑ allmain.c in NetHack 3.4.3, line 33

↑ mhitu.c in NetHack 3.4.3, line 1190

↑ timeout.c in NetHack 3.4.3, line 168

↑ allmain.c in NetHack 3.4.3, line 241

↑ mhitu.c in NetHack 3.4.3, line 1428

↑ mhitu.c in NetHack 3.4.3, line 907

↑ hack.c in NetHack 3.4.3, line 1759

This page is based on a spoiler by Dylan O'Donnell. The original license is:
Redistribution, copying, and editing of these spoilers, with or without modification, are permitted provided that the following conditions are met:

The original contributors to any spoiler must continue to be credited.
Any modifications to the spoiler must be acknowledged and credited.

This page may need to be updated for the current version of NetHack.
It may contain text specific to NetHack 3.4.3. Information on this page may be out of date.
Editors: After reviewing this page and making necessary edits, please change the {{nethack-343}} tag to the current version's tag or {{noversion}} as appropriate.