Celestial Sigil

The Celestial Sigil is a boss-summoning item crafted out of 20 of each of the Lunar Fragments. It is used to summon the Moon Lord without going through the Lunar Events. Rather than summoning the Moon Lord immediately after the item is used, it takes a minute before the Moon Lord actually appears, the same way as when all of the pillars are defeated.

The Celestial Sigil can only be used under the following circumstances:
 * The player is not able to see any Lunatic Devotee and/or Blue Cultist Archer on their screen. In multiplayer, the Cultists must be off-screen for all players.
 * Golem has been defeated.
 * There is no boss alive.
 * The Lunar Events are not active (there are no Celestial Pillars in the world), and no other event is active.

Trivia

 * The Celestial Sigil resembles the Mysterious Tablet, the strange idol near the Dungeon, which spawns along with the Cultists and is destroyed when summoning the Lunatic Cultist.
 * The four colors on the rim of the sigil represent the colors of the four Celestial Pillars and the center depicts Moon Lord's face.
 * The item was implemented to reduce the amount of time required to farm the Moon Lord. Before 1.3.0.5, simply reaching the Moon Lord could take upwards of 10 to 15 minutes.
 * Due to the high amount of fragments needed, one Lunar Event might yield just enough for 1–2 Celestial Sigils, if any at all. In Expert Mode, it is possible to get enough to make 4.
 * It is one of the two boss-summoning items that do not immediately summon the corresponding boss, the other being the Prismatic Lacewing.

History
Sceau céleste 천체의 인장 天界符