A 9×9 board by the numbers
Every Star Battle board is defined by three numbers: the grid size, the stars per line, and the region count. On a 9×9 they are 9, 2 and 9. Two stars in each of nine rows is eighteen stars; two in each of nine columns is the same eighteen; and the nine outlined regions must each hold two — the same eighteen stars, counted a third way. That triple-counting is the whole engine of the puzzle. Whenever you can show that a set of rows already accounts for its stars, you have said something about the columns and regions passing through them too.
The other number worth holding in your head is 63: the cells that are not stars. On a 9×9, more than three-quarters of the board is going to end up marked X, which is why experienced solvers spend far more time placing X's than stars. A star is a conclusion; the X's are the reasoning that gets you there.
Why 9×9 is the daily size
Most of our daily easy, medium and hard boards are 9×9, and that is a deliberate choice. Below 9, regions get so small that the puzzle solves itself; a 6×6 is a pleasant warm-up but rarely a challenge. Above 9, the region count climbs, the deduction chains lengthen, and a single board starts to want a whole lunch break. Nine is where a region averages nine cells — enough for its shape to matter, few enough that you can scan every region in a few seconds and spot the one that gives.
It is also the size at which the two-star rule does its best work. One star per line, as in Queens, makes each placement decisive but the board small. Two stars per line on a 9×9 means every row and column is a little puzzle of its own — where can two non-touching stars fit in what's left? — and those little puzzles overlap in ways that reward looking twice.
Read the region shapes first
Before any X is placed, the outline of a region already rules cells in or out.
On a 9×9 the regions are small enough that their shape alone hands you free marks. Two shapes come up constantly. The first is the compact block: a region packed into roughly a 3×3 square. Its centre cell touches all eight others, so it can never be a star — if it were, the region's second star would have nowhere to go.
1 A compact 3×3 region. Its centre cell touches every one of the other eight.
2 The region needs two stars that don't touch. A star in the centre would touch the second one wherever it went — so the centre is X'd before you place anything.
The second is the sliver: a region only three cells long in a straight line. It still needs two stars, and two non-touching stars can only sit at its two ends. That is two stars placed, one X in the middle, and twelve more X's radiating out from the pair — before you have deduced a single thing. Slivers are the single best opening a 9×9 can offer, and our step-by-step solutions call this move out by name whenever it appears.
1 A three-cell sliver in a straight line. Two stars have to fit in it without touching.
2 Only the two ends can do that. Both stars are placed at once, the middle is X'd, and the no-touch rule clears twelve more cells around them.
The moves that matter at 9×9
Three techniques do most of the work on this board size. All of them come from the strategy guide.
Confined regions
With nine regions on nine rows, it is common for a region to sit entirely inside one row or one column. When it does, it claims both of that line's stars, and the rest of the line can be X'd on the spot. Scan for this first on every fresh board.
1 This region sits entirely inside one row — both of that row's stars must fall inside it.
2 The rest of the row can never hold a star — X it out.
Completion
The moment a row, column or region is down to two open cells, both are stars; the moment it has its two stars, everything else in it is an X. On a 9×9 these cascade quickly — one completion opens the next — so after every placement, sweep all nine rows, nine columns and nine regions before you look for anything cleverer.
1 Three of this region's five cells are already X'd — only two remain open.
2 A region needs exactly two stars, so both open cells must be stars. Rows and columns work the same way.
Counting a band
Any two adjacent rows hold exactly four stars. If two regions fit entirely inside those rows, they need four stars between them — the band's entire quota — and every other cell in the band is out. On a 9×9 there are eight such two-row bands and eight two-column bands, and at least one of them usually gives.
1 The top two rows hold exactly four stars — and these two regions, which fit entirely inside them, also need exactly four.
2 Those regions consume the whole quota, so every other cell in the two rows is X'd.
A typical 9×9 solve
Most 9×9 boards unfold in three recognisable phases.
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1
The opening: shapes and confinements
Read the outlines. X any block centres, place any sliver pairs, and look for regions trapped in one line. A good 9×9 yields ten to twenty marks here without a single chained deduction. If you find none, the board is telling you it is a hard one — slow down.
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2
The middle: completions and counting
Now the X's start closing lines. Sweep for rows, columns and regions with two cells left or two stars in. When that stalls, count a two-row or two-column band against the regions inside it. This phase is where the board's difficulty actually lives.
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3
The finish: the cascade
Somewhere past the halfway point a 9×9 tips over. Each star forces two or three more and the last third of the board fills in seconds. If it doesn't — if you are staring at an open board with no forced move — you have missed an X earlier. Walk back through the regions before you guess.
Stuck on a real board? Every daily puzzle has a free step-by-step solution that names each deduction as it happens, so you can find the exact move you missed rather than the whole answer.
9×9 or 10×10?
The other size we publish is 10×10, the grid you will recognise from the New York Times' Two Not Touch. One extra row and column sounds small. In practice it adds a tenth region, two more stars, and noticeably more room for the constraints to overlap.
Pick 9×9 for a daily habit and for learning technique; the board is small enough that every move is easy to see in hindsight. Pick 10×10 when you want a longer sit, or when you are coming from the newspaper and want the board you already know.