What is Tentai Show (Spiral Galaxies)?

Tentai Show (meaning 'astronomical show' in Japanese, popularized internationally as Spiral Galaxies or Galaxies) is an iconic Nikoli logic puzzle. Players partition an entire grid into connected regions where each region possesses 180-degree rotational symmetry around a center dot.

Where can galaxy dots be located?

Dots can appear in three locations: the center of a grid square, on an edge between two squares, or at a vertex intersection where four squares meet.

What does 180-degree rotational symmetry mean?

A shape has 180-degree rotational symmetry if it looks completely identical when rotated half a turn (upside down) around its center dot. For every cell in the galaxy, its opposite counterpart through the dot must also be part of that same galaxy.

Can galaxies overlap or leave empty squares?

No. The entire grid must be seamlessly tiled by galaxies. Every square must belong to exactly one galaxy with zero gaps and zero overlaps.

Can a galaxy contain multiple dots?

No. Each galaxy must contain exactly one nucleus dot.

What is Tentai Show (Spiral Galaxies)?

Tentai Show (meaning 'astronomical show' in Japanese, popularized internationally as Spiral Galaxies or Galaxies) is an iconic Nikoli logic puzzle. Players partition an entire grid into connected regions where each region possesses 180-degree rotational symmetry around a center dot.

Where can galaxy dots be located?

Dots can appear in three locations: the center of a grid square, on an edge between two squares, or at a vertex intersection where four squares meet.

What does 180-degree rotational symmetry mean?

A shape has 180-degree rotational symmetry if it looks completely identical when rotated half a turn (upside down) around its center dot. For every cell in the galaxy, its opposite counterpart through the dot must also be part of that same galaxy.

Can galaxies overlap or leave empty squares?

No. The entire grid must be seamlessly tiled by galaxies. Every square must belong to exactly one galaxy with zero gaps and zero overlaps.

Can a galaxy contain multiple dots?

No. Each galaxy must contain exactly one nucleus dot.

Nikoli Classic • Tentai Show / Spiral Galaxies

Galaxies (Tentai Show)

Harness cosmic symmetry! Divide the grid into swirling galaxies such that each shape has 180° rotational balance around its glowing center dot.

5x5 Spiral Orbit5x5 Grid • 7 Spiral Galaxies

0:00

1/7 galaxies valid

Click dot to select galaxy • Tap cells to expandTiled: 1/25

Plotting spiral galaxy nuclei...

Tentai Show Rules & Celestial Mechanics

Published by Nikoli and made globally famous by Simon Tatham, Tentai Show (“Galaxies”) is a masterclass in two-fold geometry:

1. One Core Per GalaxyEach galaxy must enclose exactly one cosmic dot. Dots can reside on cell centers, grid edges, or corners.

2. 180° Rotational SymmetryEvery galaxy must have 2-fold rotational symmetry around its dot. If rotated upside down, the shape must map perfectly onto itself.

3. Seamless Grid PartitionEvery square on the grid belongs to exactly one galaxy. There are zero unassigned cells and zero overlapping territories.

4. Single Connected RegionThe squares forming each galaxy must be orthogonally connected together into a single continuous shape.

Galactic Deduction Strategies

1. Edge & Center Nucleus Seeding

If a dot is in the center of a cell, that cell must belong to that dot. If a dot is on an edge between two cells, both adjacent cells must belong to that dot! Start every puzzle by claiming these initial seeds.

2. Corner Cell Forcing

Inspect the 4 outer corners of the grid. For each corner cell, test which dots can geometrically reflect that corner without flying off the grid. Often, only one single dot can legally reach that corner!

3. Wall Reflection Collision

Whenever a galaxy hits a boundary wall or an established foreign galaxy, its $180^\circ$ opposite edge must also form a wall! Symmetrical walls immediately restrict the expansion of neighboring galaxies.

4. Auto-Reflect Pairing

Keep Auto-Reflect enabled in our interactive player. Tapping any square instantly pairs its symmetric twin, keeping your focus on spatial deduction and region borders!

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