Moon phase

Each night the moon advances one step, and the loop runs eight nights end to end. A fresh world opens on a full moon, drops through three waning steps to a new moon on the fourth night, then climbs back through three waxing steps to full again. Nothing resets it and nothing skips it, so once you know tonight you know the whole week.

The switch happens at dawn, at 4:30 AM, not at dusk. A phase therefore covers the daytime that comes before its night. If a shop line or a fishing bonus is tied to the full moon, it is already live while the sun is up, and it ends the following morning rather than at nightfall.

The Sextant puts the current phase straight into your info bar. It comes out of the Angler quest reward pool, so it is worth chasing early if you fish seriously, and every later accessory that absorbs it keeps the readout.

Without one, two town NPCs give it away. The Painter rotates his paintings by moon quarter, and in Hardmode the Clothier rotates clothing the same way. That narrows it to a quarter rather than an exact night, which is usually enough. Otherwise just look up: the lit edge sits on the right while the moon is filling and on the left while it empties.

Fishing is the effect you will notice first. A full moon multiplies your fishing power by 1.1 and a new moon cuts it to 0.9, with the phases in between stepping through 1.05 and 0.95 and the two quarters sitting at neutral. Ten percent either way sounds small, but on a marginal rod and bait setup it is the line between pulling crates and pulling junk, and waiting four nights costs nothing.

A few spawns key off it as well, most visibly the Werewolf, which only appears on the surface at night under a full moon in Hardmode. The Moon Charm gives you the same transformation on any night, so the enemy is the phase-locked half of that pair, not the item.

The exclusion is the one to memorize: a Blood Moon can roll on any phase except a new moon. That makes the new moon night the single night of the cycle when building outdoors is safe without checking the sky first. Pumpkin and Frost Moons are summoned by hand and ignore the cycle entirely.

• Drinking a Bloody Tear on a new moon nudges the phase forward to waxing crescent, since the event it forces cannot start on a new moon.
• Each world is assigned one moon sprite when it generates. The Moon Globe lets you swap it later, and the Frost and Pumpkin Moon events override the art with their own for the night.
• During those events on a partial phase, the event sprite is still trimmed to the shape of the current phase rather than shown whole.
• The lit side switches from right to left as the cycle turns, which places Terraria's world in its planet's northern hemisphere if you read the sky literally.