How to play Galaxies

Split the grid into galaxies, each holding one dot and looking the same after a half turn around it. Also known as Spiral Galaxies, Tentai Show.

▶ Play Galaxies ⊞ Open the solver

The rules

Every square must belong to exactly one galaxy.
Each galaxy contains exactly one dot.
Each galaxy has rotational symmetry around its dot: turn it 180° around the dot and it lands exactly on itself.
Galaxies are joined pieces — no galaxy is split in two.

Playing Galaxies on Puzzle Solvers

Choose a size, how big the galaxies are and a difficulty, then press New Puzzle.
Tap a dot to pick its colour, then tap or drag across squares to paint them. Auto-mirror paints the matching square on the other side of the dot for you.
Tap a painted square again to clear it, or use Erase. Finished galaxies light up and their dot turns gold.
Hint explains which dot must own the next square and why.

Open the Galaxies game →

Using the Galaxies solver

Choose the size and click where each dot is (or press Sample). Click a dot again to remove it.
Press Solve and step through: the squares each dot touches, mirror images, squares only one dot can reach, and what-ifs.

Open the solver →

A worked example

A dot sits on the line between R1C1 and R1C2, so both squares belong to it. R2C1 could join it only together with its mirror R0C2 — which is off the grid.

So R2C1 can't belong to that dot, and if the only other dot that reaches it is the one in R3C1, R2C1 joins that one — along with its mirror R4C1.

Strategies

Start at the dots. A dot in a square owns that square. A dot on a line owns both squares beside it. A dot on a corner owns all four squares around it.
Mirror everything. Whenever a square joins a galaxy, its partner — the square the same distance from the dot on the opposite side — joins too.
Off the edge. A square can't join a dot if its mirror image would land outside the grid or on a square already taken.
Who can reach it?. If only one dot can claim a square, that square is theirs.
Close the borders. Draw a wall between squares of different galaxies; corners and edges of the grid are often settled first.

Common mistakes

Forgetting to paint the mirror square too — turn on Auto-mirror to avoid it.
Making a galaxy that is symmetric around the wrong point.
Leaving a lone square that no dot can reach — every square needs a galaxy.

Where it comes from

Galaxies (Tentai Show, ‘astronomical show’) was created by the Japanese puzzle company Nikoli. In some versions black and white dots make the finished galaxies reveal a picture.

Frequently asked questions

Do galaxies have to look like spirals?

No — any shape works as long as it looks the same after a half turn around its dot. Many are rectangles, crosses or zig-zags.

What does auto-mirror do?

When you paint a square, the matching square on the opposite side of the dot is painted too.

Is there always one answer?

Yes — every puzzle here is checked to have exactly one way to split the grid.

How do I solve one from a book?

Open the Galaxies Solver, click where the dots are and press Solve.

Keep going

All guides: How to play every puzzle and game.