What is Galaxies?
Galaxies is a visual logic puzzle where the grid must be divided into regions. Each region is called a galaxy, contains exactly one star, and has 180-degree rotational symmetry around that star.
That means every cell you add to a galaxy needs a matching cell on the opposite side of the star. Some stars sit inside a cell, some sit between two cells, and some sit at the meeting point of four cells, so the symmetry can be odd or even.
- Divide the whole grid into galaxies.
- Every galaxy contains exactly one star.
- Every galaxy is rotationally symmetric around its star.
- Galaxies cannot overlap and every cell must belong to one galaxy.
- The playable boards on this page prioritise interesting rotational shapes and include one intended solution for the helper tools.
How to play Galaxies online
Select a coloured star, then click or tap cells to assign them to that galaxy. If a cell belongs somewhere else, select the correct star and repaint it. The goal is a complete grid where each coloured area rotates cleanly around its own star.
Use Check for feedback without revealing the full answer. Hint fills one useful cell from the intended solution, and Solution shows the completed galaxy map if you want to study the pattern.
- Start with stars on corners, edges or tight spaces.
- Look for cells that can only mirror to one legal partner.
- When you fill a cell, check the opposite cell around the same star.
- Avoid letting two galaxies fight over the same mirrored pair.
- Use larger empty spaces last, once the forced small galaxies are clear.
Galaxies grid sizes and difficulty
Smaller Galaxies grids make the symmetry easy to see, so they are good for learning the rule. Larger grids create longer boundaries where one forced cell can decide the shape of several nearby galaxies.
Easy puzzles use more compact regions and more obvious symmetry. Medium puzzles mix small and larger galaxies. Hard puzzles leave more open space, so you have to combine local mirror logic with whole-grid partitioning.
- 6x6 Galaxies is a friendly starting size.
- 8x8 Galaxies gives a balanced daily puzzle.
- 10x10 Galaxies offers more room for bigger symmetric regions.
- Easy, medium and hard change the region shapes and solving pressure.
- New puzzle loads another checked board for the chosen setting.
Galaxies strategy tips
The best Galaxies strategy is to think in mirrored pairs. For any star, imagine rotating a chosen cell halfway around the star. If the matching cell is outside the grid or already forced into another galaxy, that choice cannot work.
Boundaries matter too. A galaxy must stay connected, so a tempting mirrored pair can still be wrong if it cuts the region into separate pieces or blocks a nearby star from having any legal shape.
- Mark the core cells around each star first.
- Use the edge of the board to rule out impossible mirrors.
- Pair cells symmetrically instead of growing one side only.
- Watch for stars whose surrounding cells are already nearly decided.
- When stuck, scan the smallest unfilled gap between two stars.
Why interesting Galaxies shapes matter
Many published Galaxies puzzles aim for a provably unique final partition, but the most memorable boards also need lively, irregular regions that make the symmetry fun to read.
This online version now favours richer rotational shapes. Check, Hint and Solution all use the same intended galaxy map, while the hard boards are designed to look more like advanced Galaxies puzzles.
Stars on edges and corners
Before any clever symmetry, the position of each star hands you free cells. A star printed inside a cell instantly claims that cell. A star sitting on the line between two cells claims both of them, because they are 180-degree mirrors of each other. A star at the corner where four cells meet claims all four. Filling these guaranteed cells first gives every galaxy a solid core to grow from.
From that core, symmetry does the rest. Whenever you add a cell to a galaxy, its mirror cell on the opposite side of the star joins too, so the region always grows two cells at a time. Starting from the forced cells around each star and expanding in mirrored pairs keeps you on safe ground and quickly shows which cells are still contested.
- A star inside a cell claims that cell.
- A star on an edge claims the two cells it sits between.
- A star on a corner claims all four cells around it.
- Every cell you add forces in its mirror across the star.
- Grow each galaxy outward in symmetric pairs, never one side alone.
A worked Galaxies deduction
Symmetry also tells you where a cell cannot go. Pick a star and a nearby empty cell, then rotate that cell 180 degrees around the star to find its required partner. If the partner lands outside the grid, the cell can never belong to this star, because its mirror has nowhere to exist. One quick rotation often removes a star from contention for a whole row of edge cells.
Now combine that with reach. A cell can only join a galaxy if both it and its mirror are still free for that star and the region stays connected. When just one star passes both tests for a given cell, the cell is forced: paint it, add its mirror, and the new border usually forces the next cell in turn.
- Rotate a cell 180 degrees around a star to find its partner.
- If the partner falls off the board, that star cannot own the cell.
- A cell needs both itself and its mirror free to join a galaxy.
- If exactly one star passes the test, the cell is forced.
- Each forced pair tightens the choices for the cells nearby.
Galaxies, Tentai Show and Nikoli
Galaxies is a Nikoli puzzle, from the same Japanese publisher that gave the world Sudoku, Nurikabe and Shikaku. Its original name is Tentai Show, which translates roughly as 'astronomical show,' and in English it also appears as Spiral Galaxies. The stars and rotational regions give the puzzle its space theme.
Like other Nikoli classics, a well-made Galaxies puzzle is designed to be solved by pure logic toward a single intended partition. The version here keeps the star-and-symmetry rules and adds grid sizes from 6x6 to 10x10, so you can learn the mirror trick on a small board and then take on roomier, more irregular galaxies.