Celestial Sigil

The Celestial Sigil is a boss-summoning item crafted out of 20 of each of the Celestial Pillar's fragments. It is used to summon the Moon Lord without going through the Lunar Events. The Lunar Events must not be active (there cannot be Celestial Pillars in the world) to use the item. This item cannot be used when you are able to see any Lunatic Devote and/or Blue Cultist Archer on your screen, or when another boss has already been summoned. It also cannot be used in a world in which Golem has not been defeated or if there is another event going on, like the Pirate Invasion. Note that 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.

Trivia

 * It resembles the Mysterious Tablet, the strange idol near the Dungeon, which helps trigger the Lunar Events.
 * 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 Celestial Invasion event might yield just enough for 1-2 of these, if any at all. In Expert Mode, it is possible to get enough to make 4.
 * It is the only boss summoning item that does not immediately summon the corresponding boss.

History
Sceau céleste 천체의 인장 天界符