How to solve sun & moon puzzles
Solsticio puzzles (a sun/moon take on Binairo, Takuzu and Tango) are always solvable by pure logic — you never have to guess. Here are the techniques that crack every board, from the first move to the last.
The three rules, quickly
- No three in a rowNever ☀☀☀ or ☾☾☾ in a line, across or down.
- BalanceEach row and each column has the same number of suns and moons.
- Connectors (= and ×)= means the two cells match; × means they differ.
New to it? Start with the rules explained. Below we turn those rules into moves.
Technique 1 — The pair forces a gap
Two of the same symbol side by side force their neighbours. If you see ☀☀, the cells on either side must be ☾ (a third sun would make three in a row):
☾ ☀ ☀ ☾
The same works with a gap: ☀ _ ☀ must be ☀ ☾ ☀, because a sun in the middle would make three:
☀ _ ☀ → the gap must be a moon.
Technique 2 — Finish the edge
A pair against the wall forces the third cell too. ☀☀ _ at the start of a line must continue ☀☀☾. Scan every row and column for two-in-a-rows touching an empty cell — each one is a free move.
Technique 3 — Balance the line
Every line holds the same number of suns and moons (three of each on a 6×6, two of each on a 4×4). So the moment a row or column reaches its quota of one symbol, every remaining cell is the other symbol. On a 6×6, once you place the third sun in a row, the rest are moons:
☀ ☾ ☀ ☾ ☀ ☾
Five cells filled with three suns → the last one must be a moon.
Technique 4 — Cross-reference rows and columns
A cell lives in a row and a column. If the row rule leaves two options but the column rule forbids one of them, the cell is decided. When you're stuck, pick an empty cell and ask: “would a sun here break its row or its column?” Often one symbol breaks a rule and the other doesn't — that's your move.
Technique 5 — Follow the connectors
On later worlds, = between two cells means they're equal and × means they're different. Treat them as extra constraints: if one side of a = is known, so is the other; a × next to a known cell fixes its neighbour. Connectors often start a chain that unlocks the rest of the board.
A fully solved board
Chain these ideas and there's never a dead end — only the next forced move, until the grid completes:
The golden rule: never guess
Every Solsticio board is verified to have exactly one solution reachable by deduction. If you can't find a move, you've missed one — re-scan for pairs and full lines rather than guessing. Guessing is never required, and it's usually slower.
Prefer your phone? The free Android app has hundreds of levels and a daily puzzle.