Lunar Events

The Celestial Events are a series of four Hardmode, post-Plantera events initiated by defeating the Lunatic Cultist boss. Once the boss is defeated, several surface biomes show a large moon in their backgrounds, and spawn several unique enemies. The moon biomes will spawn in four distinctly spaced sections of the world. Defeating the pillar will revert the area back to normal. In order to defeat any of the four pillars, one must first kill 100 monsters (150 in Expert Mode) corresponding to the selected pillar in order to remove the barrier that is protecting it. To find where these pillars are, open your map. There will be icons of each pillar which will show where it is.

Each of the four variants has a different theme, along with a corresponding Celestial Tower variant that acts as the centerpiece of the event.

Upon defeating all four pillars, the message "Impending doom approaches..." appears in chat. The screen begins to shake, and approximately one minute later the Moon Lord will spawn on top of the player.

Tips

 * Destroy the Nebula Pillar first, as it grants access to the Nebula Blaze, an extremely fast and powerful homing magic weapon that will help take down the other three pillars. The Nebula Pillar can be easily taken down with a Razorpine and healing variant of the Spectre Armor.Another option is the defeat the Vortex Pillar and get the very powerful Vortex Beater, which with Shroomite Armor equipped, you can easily take down the other three pillars.
 * Going after the Vortex Pillar first will also allow you to create the Phantasm. With proper arrows and good aim, you can easily achieve upwards of 4,000 DPS. With this damage, it's possible to destroy the other Celestial Towers in 3-4 seconds.
 * When fighting the Solar Pillar, take into account that the Crawltipede does not target players on the ground. Knowing this, you can easily defeat the pillar while staying on the ground.
 * when fighting against Stardust Pillar, try using an area of effect weapon, such as Inferno Fork to kill star cells, the battle may keep indefinitely, as the small cells flee and grow, to attack again, making easy to reach more than 300 kills.
 * After defeating the Lunatic Cultist make sure that you pick up the Ancient Manipulator. If you are not well-equipped for the Lunar Events then you may die quickly and not be able to retrieve it afterwards.
 * Every pillar and its enemies has a different theme and items: nebula is magical, solar is melee, vortex is ranged and stardust is summon items/swarm enemies.
 * The pillars and their minions retain their damage, regardless if you die.
 * For melee players, the vampire knives are extremely helpful against any of the celestial pillars.
 * The Lunar Events are actually made up of two events: Celestial (The Pillars) and Lunar (Moon Lord)

History
Événements Lunaires