Sudoku Made and maintained by Brian Hamilton and Karan Hamilton.
Brian builds the playable puzzle tools, while Karan helps test clarity, difficulty feel, and the player experience.
Playable puzzles and controls are tested in the browser for rule accuracy, usability, and a clear solving experience. See how we make and test puzzles, our editorial standards, or report a problem.
A space-themed sudoku for any week of the year
Space Sudoku launches classic sudoku into orbit, with nine pictures from the night sky in place of the digits: a rocket, a planet, a star, the moon, the sun, a comet, an alien, a telescope and a galaxy. One law of physics holds on every board: a picture never repeats in a row, column or box. For the views, the board sizes and what each level asks of you, which never change across our 21 picture games, ground control is the Themed Sudoku page.
Most of our picture boards belong to a holiday or a season. Space doesn’t. It belongs to whoever is obsessed with it this month, which in our experience is always somebody, and it suits a school space-topic week as well as a wet Saturday.
Why is there no alien on the small boards?
Smaller boards take only the start of the set. The 4×4 has the 🚀 Rocket, 🪐 Planet, ⭐ Star and 🌙 Moon, numbered 1 to 4. The ☀️ Sun (5) and ☄️ Comet (6) join on 6×6, the game’s opening size, and the 👽 Alien (7), 🔭 Telescope (8) and 🌌 Galaxy (9) only turn up on the full 9×9.
That order is simply how every game here deals its pictures, but we like the story it tells: you have to earn the alien. It takes the biggest board to meet one, and the telescope arrives on the same board.
For a young solver’s first flight, start on 4×4 Easy. Ten of its sixteen squares come filled in, and its four pictures look nothing alike. The one picture that can pass for the star, the sun, waits on 6×6. Six squares to fill is a finished puzzle before the attention span burns up on re-entry.
Is that a star or the sun?
Space is full of things that shine, so the worry with this set was its bright tiles blurring together on a small screen. Phone-width Windows screenshots of all three sizes, light and dark, turn up one pair that needs a second look: the ⭐ Star and the ☀️ Sun. Both are gold and about the same size. The Star has five rounded points; the Sun is a round disc with a wavy orange rim. They first meet on 6×6.
The rest of the sky behaves. The ☄️ Comet is a red ball trailing a pale tail, nothing like either. The Moon is a thin crescent and the Planet wears a gold ring, so those two don’t pass for each other. In the dark theme the Galaxy’s own square of night sky nearly vanishes against the board, so it reads as a blue streak of stars, but no other tile looks like it. That is the Windows sky; other phones paint their own.
If the pair still catches you, Both settles it with a number in the corner of every square: the Star is 3 and the Sun 5. Of our 21 picture games, this is the only one that deals both, so it is the one board where that mix-up can happen.
Astronomers would forgive the mix-up: the Sun is a star, the nearest one to Earth. The 🌌 tile is the emoji Unicode names MILKY WAY, the galaxy the Sun belongs to, and the 🪐 is its RINGED PLANET, drawn with a ring like Saturn’s, though Jupiter, Uranus and Neptune have rings too. The game ignores all of it: tiles 3 and 5 are different pictures, and on 6×6 and 9×9 every row needs one of each.
How do you find the alien on a 9×9 board?
Let the aliens already on the board do the searching. Pick a line with no Alien yet: below, it is column 7 of a 9×9 Medium board the game really dealt. An Alien shuts every other square of its own row and box to Aliens, so any empty square of the column that shares a row or a box with one is out. When one square is left, the Alien lands there, no matter what else might fit. That is a hidden single, found down a column.
Nothing else decides it: R1C7 could still be the Planet or the Sun, and row 1 and the top-right box have other places for an Alien. Fittingly, the column’s Telescope is already in place at R7C7. Like every Medium board here, it is dug so that hidden and naked singles see it through; the game’s own singles carried this one to the last square when we ran them, and a separate solver counted one answer.
Does Space Sudoku teach astronomy?
No, and we would rather say so. It won’t teach the order of the planets or what a comet is made of. It teaches scanning, ruling things out and giving a reason for every move, the way the caption above argues its alien into R1C7. The space pictures are the hook, not the lesson, and the hook works.
For a space-topic week, pair the puzzle with the real sky: after a 4×4, ask which of its four pictures a child could see from home on a clear night without a telescope. Three of them: the Moon, the stars, and planets such as Venus and Jupiter, which look like bright stars. Sudoku for Kids takes the rules one step at a time, at home or in class.
If the obsession is dinosaurs instead, Dinosaur Sudoku deals the same comet picture as its Meteor, and its page explains why.