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For a list of other rooms featured in Antibirth, check out Chapters.


The Planetarium is a new unlock-able room type introduced in Antibirth that has a small chance to appear after certain criteria are met. Like Treasure Rooms, they require a key to enter.

Planetariums are unlocked by acquiring three astrology-related items in a single run. These items include the Signs of the Zodiac, Tiny Planet, Magic 8 Ball, and Crystal Ball.

The chance for a Planetarium to appear starts at 1% and will increase by +20% whenever a Treasure Room is skipped. The Treasure Room must not be entered at all to be considered skipped. This chance is further increased by an unknown percentage if Isaac has Magic 8 Ball or Crystal Ball. If Isaac enters a Planetarium, the chance will be set to 0% and can't be increased again

These rooms also have a chance to spawn in the purple-tinted areas of the Mausoleum, without Isaac previously skipping any Treasure Rooms.

Planetariums are similar to Treasure Rooms, but only contain special astronomy-themed items that are only available through Planetariums. They may also contain Signs of the Zodiac.

If a Planetarium spawns on one of the alternative floors where Treasure Rooms would normally have 2 items to choose from, the Planetarium may still only have one item with no other choice available.

Planetarium Items[edit | edit source]

Name Icon Description
SolSol Icon.pngActivates the Sun tarot card and fully recharges Isaac's active item upon defeating a boss. Reveals the location of the Boss room on the map.
LunaLuna Icon.pngAdds one extra Secret Room and one Super Secret Room on each floor.
MercuriusMercurius Icon.pngDoors stay open after entering a room, even with enemies in it, allowing Isaac to leave any time. Increases speed.
VenusVenus Icon.pngEnemies near Isaac will be inflicted with Charm that wears off quickly after enemies move away from Isaac, causing enemies to attack each other.
TerraTerra Icon.pngIsaac's tears become rocks. The tears can also destroy rocks.
MarsMars Icon.pngGain the ability to charge by double-tapping in a direction. Isaac is invincible during the charge and deals significant damage. Can be used multiple times per room with a short recharge time.
SaturnusSaturnus Icon.pngIsaac is surrounded by an aura which grants 7 orbiting tears when entering a new room and has a chance to absorb incoming enemy tears.
UranusUranus Icon.pngIsaac shoots ice tears.
PlutoPluto Icon.pngDecreases Isaac's size to the point where many tears will fly over Isaac. Increases tears and speed, and decreases range.

Zodiac collectibles from the base game are placed in Planetarium item pools:

Trivia[edit | edit source]

  • The Planetarium concept started out as a mod request on Reddit.[1]
  • All of the Planetarium items resemble celestial bodies from the Solar System: Sol and Luna resemble the Sun and the Moon respectively, while the rest of the items stand for the planets from Mercury to Pluto.
    • Jupiter and Neptune are the only planets in the Solar System not represented by any items of this kind.
      • Oddly, Pluto is not considered a planet by the scientific community since 2006 but does have a Planetarium item named after it.
  • All of the items' names are written in Latin (though some of these Latin names are shared with modern languages):
    • "Sol" and "Luna" are both Latin for "Sun" and "Moon".
    • "Mercurius" and "Terra" are Latin for "Mercury" and "Earth".
    • Actually, the name of "Saturnus" does not mean "Saturn" in Latin. Rather, it appears to be using the planet's Dutch name, or is simply mistranslated by having the suffix "-us" added to the planet's English name.
    • The names of Venus, Mars, Uranus and Pluto are in English.
  • The tarot card, The Stars, prioritizes a Planetarium over a Treasure Room. This is probably because a Planetarium is more related to the stars.

Sacdag.png Antibirth Sacdag.png

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