Guess today's identifier in 6 tries. Every guess must be a real entry in one of the catalogues: Messier (M), NGC, IC, Melotte (Mel), Collinder (Cr), Caldwell (C) and Barnard (B). Each object is in the game once, under the identifier most people know it by: the Andromeda Galaxy is M31, and guessing NGC224 tells you so.

You type the full identifier: the catalogue prefix, then the number without leading zeros (NGC 42 is NGC42, the Hyades are Mel25), plus a component letter if the object has one (A–F, e.g. NGC1023A). Any character can go in any tile; tiles you leave empty when pressing Enter count as blanks, so just type the identifier and hit Enter. To change one character, click its tile (or use ← →) and type over it.

Puzzles before 5 October 2026 (#0–#26) use only NGC and IC. A puzzle you played before then keeps the zero-padded spelling it was played in (NGC0042); Reset puzzle starts it afresh in today's.

Above the board, ✖ counts the guesses that were refused (not a known identifier, another id of an object in the game, a repeat, or breaking hard mode) — it also goes into the share text.

After each guess the tiles show how close you are: green = right character, right place; yellow = in the identifier, wrong place; grey = not in the identifier.

The panel left of the board describes each guessed object: constellation, object type (click it for an explanation), magnitude, and the angular distance to the target with an arrow pointing towards it (north up, east left, as on the sky). green = matches the target (distance/magnitude: very close), yellow = nearly. Type and magnitude come from SIMBAD and need a network connection.

Click a submitted guess row to see that object in a sky view right of the board; when the game is over the view shows the target, and clicking guesses lets you compare. The Constellations button under the view draws every constellation's border, figure and name.

Hard mode is on by default (toggle in settings ⚙): every guess must be one that could still be the answer. Green tiles stay in place; a character can't go back to a tile where it was yellow or grey, even if it is green elsewhere; and the counts must fit: a grey 1 next to a green 1 means there is exactly one 1, and a character that was only ever grey isn't there at all. Since greens are locked in anyway, each new row starts with them already filled; typing fills the remaining tiles and Backspace skips the greens. The line above the board shows how many identifiers could still be the answer.

Unlimited: once you have finished today's puzzle, won or lost, switch from Daily to Unlimited (beside the puzzle number) and solve random objects one after another, as many as you like. A stopwatch runs from your first key, paused while the page is hidden. Unlimited keeps its own stats; your daily streak and history stay as they are.

Switch to ABC mode (toggle by the title) to guess the object's common name instead of its catalogue number.

A new puzzle appears every day at midnight (local time).

MUL 𒀯 — Sumerian for “star”, after the oldest known star catalogues: the Babylonian “Three Stars Each” lists (cuneiform: MUL.MEŠ 3.TA.ÀM, c. 12th century BC) and their successor MUL.APIN.