Planetarium

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. The Treasure Room must not be entered at all to be considered skipped. This chance is further increased by 9% with Telescope Lens, by 15% with Magic 8 Ball, and by 15% with 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. However, the bonus will remain intact for a later level if any remain.

Planetariums can also not normally be encountered after II, though Telescope Lens allows them to appear in .

Planetariums are unlocked by acquiring three different astrology-related items in a single run.

These items include the Signs of the Zodiac, Card Reading, Crystal Ball, Deck of Cards, Echo Chamber,Magic 8 Ball, Tarot Cloth, Star of Bethlehem, Zodiac, and Planetarium items.

The Crystal Ball and Deck of Cards will not count towards the unlock if they are left behind after picking them up, they must be actively held.

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 simultaneously.

Even though Planetarium items are locked behind Planetariums, they are possible to obtain before unlocking the rooms by any random item drops that ignore the item pools (like Eden).

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

Notes

• 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 from the Bag of Crafting will not guarantee the Planetarium achievement.
  • However, acquiring the regular Zodiac items via Bag of Crafting will grant the achievement, and items such as Aquarius are relatively easy to craft.
• A rare Planetarium layout with two items exists. Only one can be taken.
• Planetariums will not be available on challenges that prevent Treasure Rooms from spawning.
  • During Pica Run, a Planetarium will contain only a trinket.

Items

Name	ID	Icon	Quote	Description	Quality
Jupiter	5.100.594		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 afterwards.	2
Luna	5.100.589		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 Fire Rate for the current floor and gives a Half Soul Heart.	2
Mars	5.100.593		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		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		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		Size down	+0.7 tears. Significantly shrinks Isaac, allowing him to squeeze between objects and makes some enemy shots pass over him.	3
Saturnus	5.100.595		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.	2
Sol	5.100.588		Radiant victory	Reveals the location of the Boss Room. Upon defeating a boss, activates XIX - The Sun, fully recharges Isaac's active item, grants bonus damage and luck for the rest of the floor, and removes curses.	2
Terra	5.100.592		Born to rock	+1 Damage. Replaces tears with rocks that deal variable damage, have increased knockback, and can destroy obstacles.	3
Uranus	5.100.596		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		HP up + you feel pretty	Adds one red Heart container. Heals 1 additional Red Heart. Enemies near Isaac become charmed.	2

General Strategy

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, 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 or Dream Catcher can be used to check the contents of a Treasure Room without negatively affecting the chances for a Planetarium to spawn.

Statistics

Without 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 I and I.

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

Seeds

PC 0WVE F74D (Planetarium adjacent to spawn)

PC 0FYV B9EG (Planetarium adjacent to spawn)

PC NEHY 83K3 (Planetarium adjacent to spawn)

PC LCHN M6M8 (Planetarium adjacent to spawn)

PC R1J1 QPDL (Planetarium adjacent to spawn)

PC KKYJ A07S (Planetarium adjacent to spawn)

PC NMMF V0RH (Planetarium adjacent to spawn)

Gallery

• 

  The Planetarium Room

• 

  Unlocking the Planetarium

• 

  Achievement icon from unlocking the Planetarium

Bugs

Bug!	If a Planetarium spawns in the special version of Mausoleum II accessed through the strange door, it will pull from the Treasure Room item pool.

References

The Binding of Isaac: Rebirth
Achievements Challenges Completion Marks Items Trinkets Characters Chapters Rooms Transformations Attributes Bosses Monsters Pickups Modes Curses Objects Seeds Effects Endings
Collection Item Pools Version History Modding Music