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Added in Repentance

Planetarium door locked.png Planetarium door.png

The Planetarium is a new unlockable room type added in The Binding of Isaac: Repentance. They require a key to enter.

The chance for a Planetarium to appear starts at 1% and will increase by +20% whenever a Treasure Room is skipped[1]. The Treasure Room must not be entered at all to be considered skipped. This chance is further increased by 9% with Telescope Lens Telescope Lens, by 15% with 15►Magic 8 Ball Magic 8 Ball, and by 15% with 15►Crystal Ball Crystal Ball. The Crystal Ball bonus is 100% if a Treasure Room has been skipped. If Isaac enters a Planetarium, the chance will be set to 1% and can be increased only with a Telescope Lens, by 15%.

Note that the bonuses are additive, not multiplicative and can reach 100%. However, only an attempt by the game to generate a Planetarium is guaranteed: they have the lowest priority in level generation and if the level does not have enough space, the room will not be placed, the bonus intact for a later level if any remain.

Planetariums can also not normally be encountered after The Depths The Depths II, though a Telescope Lens allows them in The Womb The Womb.

Planetariums are unlocked by acquiring three different astrology-related items in a single run. These items include the Signs of the Zodiac, Magic 8 Ball, Crystal Ball, and 15►Star of Bethlehem Star of Bethlehem. The Crystal Ball will not count towards the unlock if it is left behind after picking it up. If you lose the passive items (ie: using the D4) they will not count towards the unlock. In other words, Isaac must have 3 items at the same time. Note that the item 15►Zodiac Zodiac does not count.

Planetariums are similar to Treasure Rooms, but only contain special astronomy-themed items that are only available through Planetariums.

Note[edit | edit source]

A simple way to unlock Planetarium is to acquire a D20 in Greed Mode and re-roll the coins to keep buying store items (this requires a battery to recharge the D20). The item pool includes Magic 8 Ball and all Treasure Room items (all zodiac signs); therefore, it can easily be unlocked.

Acquiring the astrology-related items (non-Zodiac items such as 15►Magic 8 Ball Magic 8 Ball, 15►Crystal Ball Crystal Ball and 15►Tiny Planet Tiny Planet) from the 15►Bag of Crafting Bag of Crafting will not guarantee the Planetarium achievement. However, acquiring the regular Zodiac items via 15►Bag of Crafting Bag of Crafting will grant the achievement, and items such as Aquarius are relatively easy to craft.

Items[edit | edit source]

Name ID Icon Quote Description Quality
Jupiter 5.100.594 Jupiter You're a gas giant! +2 red Heart containers, -0.3 speed. Isaac builds speed while standing still, and releases poison gas clouds when he moves with increased speed. 3
Luna 5.100.589 Luna The moon's blessing shines upon you Adds an extra Secret Room and Super Secret Room to each floor. Secret Rooms contain a beam of light that increases tears for the current floor and give soul hearts. 2
Mars 5.100.593 Mars Double tap dash Dash by double-tapping the movement key, becoming invulnerable and damaging enemies. There's a short cooldown before Isaac can dash again. 2
Mercurius 5.100.590 Mercurius Speed up + you feel elusive +0.4 speed. Doors stay open after entering a room, even in rooms with enemies. 3
Neptunus 5.100.597 Neptunus Open the floodgates Isaac's mouth fills with tears over time while not firing, up to a cap. Holding the fire button will release all stored tears in rapid succession. 3
Pluto 5.100.598 Pluto Size down Significantly shrinks Isaac, allowing him to squeeze between objects and makes some enemy shots pass over him. Also gives +0.7 tears. 3
Saturnus 5.100.595 Saturnus Ring of tears Upon entering a room, a circle of tears orbits Isaac. Enemy tears have a chance to be caught in orbit, turning them friendly. 1
Sol 5.100.588 Sol Radiant victory Reveals the location of the Boss room. Upon defeating a boss, activates XIX - The Sun, fully recharges Isaac's active item, and grants bonus damage and luck for the rest of the floor. 2
Terra 5.100.592 Terra Born to rock Replaces tears with rocks that deal variable damage, have increased knockback, and can destroy obstacles. 3
Uranus 5.100.596 Uranus Ice tears Isaac shoots ice tears, which slow enemies and freeze monsters they kill. Frozen enemies slide away and explode into ice shards when touched. 3
Venus 5.100.591 Venus HP up + you feel pretty Adds one red Heart container. Enemies near Isaac become charmed. 1

General Strategy[edit | edit source]

Given the new Ascent path takes you back through previous floors it is viable to skip item rooms on the way down to improve your chances of the Planetarium spawning and then getting the items from the rooms you skipped on the way back up.

Anything that rerolls the player's inventory (such as Dice Rooms, 15►D4 D4, or Tainted Eden) can increase the value of the trade-off as a rerolled Planetarium item is much more likely to be useful than a rerolled Treasure Room item.

Items such as 15►Glowing Hour Glass Glowing Hour Glass or 15►Dream Catcher Dream Catcher can be used to check the contents of a Treasure Room without negatively affecting the chances for a Planetarium to spawn.

Statistics[edit | edit source]

Without Telescope Lens Telescope Lens, Planetarium rooms can't be found in chapter 4 and after. Since the chance to find a Planetarium depends on the number of Treasure Rooms skipped, skipping earlier ones allows for a higher cumulative chance of encountering one.

The table below presents the chances if the first Treasure Rooms are skipped. For example, if the first two are passed on, there is an 84% chance to find a Planetarium between The Basement The Basement I and The Depths The Depths I.

Treasure Rooms skipped 0 1 2 3 4 5
Chapter 1-1 1.0% x x x x x
Chapter 1-2/1.5-1 2.0% 21.8% x x x x
Chapter 2-1/1.5-2 3.0% 38.2% 53.9% x x x
Chapter 2-2/2.5-1 3.9% 51.2% 72.8% 82.0% x x
Chapter 3-1/2.5-2 4.9% 61.4% 83.9% 93.0% 96.6% x
Chapter 3-2/3.5-1 5.9% 69.5% 90.5% 97.3% 99.4% 100%
Chapter 3.5-2 6.8% 75.9% 94.4% 98.9% 99.9% 100%

Seeds[edit | edit source]

PC Hard mode only 0WVE F74D (Planetarium adjacent to spawn)

PC Hard mode only 0FYV B9EG (Planetarium adjacent to spawn)

PC Hard mode only NEHY 83K3 (Planetarium adjacent to spawn)

PC Hard mode only LCHN M6M8 (Planetarium adjacent to spawn)

Gallery[edit | edit source]

References[edit | edit source]

  1. The formula is (0.2 * (stage - treasurerooms_visited - 1)). The c and d stage variants, such as Mausoleum and Gehenna, are treated as stage + 1.

SmallIsaac.png Rooms SmallIsaac.png

Unlocked Added in Afterbirth Added in Afterbirth †
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Grave Room
Locked Added in Repentance
Treasure Room Icon.png
Treasure Room
Shop Icon.png
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Challenge Room
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Boss Challenge Room
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Secret Room
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Super Secret Room
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Black Market
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Ultra Secret Room
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Devil Room
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