How is Blue Moon different from Gaps?

Gaps is Montana, which removes the four Aces from play entirely — its rows are twelve cards long and start at a two. Blue Moon keeps all 52 cards, seats the Aces at the head of each row, and its rows are thirteen cards long.

The card one rank higher and of the same suit as whatever sits immediately to the gap's left. A gap in the leftmost column takes an Ace instead, since it has no left neighbour to match.

Why can't I fill some gaps at all?

A gap immediately to the right of another gap has no left neighbour, so nothing matches it. The same is true of a gap to the right of a King — there is no card above a King, so that slot is dead for good.

How do the redeals work?

You get two, and they are only offered when no move remains at all. Every card already seated in an unbroken run from its row's Ace stays put; everything else is gathered, shuffled and laid out again.

Are any cards hidden?

None. All 52 are face up from the first second and nothing is random after the deal, so every position can be reasoned about completely rather than guessed at.

What is the most common mistake?

Making a legal move without looking at where the new gap will appear. Every fill opens a gap where that card used to be, and opening one beside a King or another gap wastes the move entirely.

Blue Moon Solitaire - Play Online & 100% Free

Play Blue Moon Solitaire — Four Rows, Four Gaps, Every Card in Sight

Blue Moon lays all fifty-two cards face up in four rows of fourteen, then moves the four Aces to the head of the rows — leaving four gaps where they came from. Those gaps are the entire game. A gap is filled by the card one rank higher and of the same suit as whatever sits immediately to its left, and moving that card opens a new gap somewhere else. Nothing is hidden and nothing is random after the deal, so every position is a puzzle you can actually solve. Free in your browser, no sign-up.

How Do You Play Blue Moon?

Goal: make every row read Ace to King in a single suit.

Setup

Deck: one standard 52-card deck, all face up.
Grid: four rows of fourteen slots. Every slot but the leftmost of each row is dealt a card; the four Aces are then moved into those leftmost slots, leaving four gaps behind them.
Redeals: two gathered reshuffles, offered only when no move remains.

Rules

A gap is filled by the card one rank higher and of the same suit as the card immediately to its left. Moving that card leaves a new gap where it was.
A gap in the leftmost column takes an Ace, and nothing else.
A gap immediately to the right of another gap is dead — it has no left neighbour to match, so nothing can ever fill it until the card to its left is placed.
A gap to the right of a King is dead too: there is no card above a King.
When no move remains, you may gather every card that is not yet seated in a run from the left of its row, reshuffle them, and lay them out again. You get two such redeals.
You win when every row reads Ace to King in one suit.

Blue Moon Strategy

With four gaps and no hidden cards, the whole game is about which gap you spend next — because every move you make destroys one gap and creates another somewhere you may not want it.

Never move a card just because you can. Every fill opens a gap where that card used to be. Before you play, look at what will be to the left of the new gap: if it is a King, or another gap, you have just spent a move to create a dead slot.
Build the rows from the left. A card is only truly safe once it sits in an unbroken run from its row's Ace. Cards further right can always be disturbed again, so lengthening a real run beats making an isolated match.
Watch the Kings. Four Kings each kill the slot to their right permanently, which is where most of a lost game's dead space comes from. Getting a King to the far right end of a row — where it belongs — is worth planning several moves ahead.
Save your redeals for a genuine stall. They are only offered when nothing at all can move, so you cannot waste one by accident — but a redeal reshuffles everything that is not seated, and a board with three long runs loses far less to it than a board with none.
Read the whole grid before your first move. Fifty-two visible cards and four gaps is a lot of information and none of it will change on its own. The opening minute is the cheapest time to find the plan.

Blue Moon in the Gaps Family

Blue Moon belongs to the grid family usually named after Montana or Gaps — games with no piles at all, where the board is a rectangle of slots and the holes in it are the mechanism. The PySol Fan Club collection parameterises the whole group with three numbers, and Blue Moon's are RLEN, RSTEP, RBASE = 56, 14, 0: fifty-six slots in rows of fourteen, with a leftmost gap accepting an Ace.

The difference from Gaps is larger than the extra column suggests. Gaps is Montana, which takes the four Aces out of play entirely: its rows are twelve cards long, they start at a two, and a leftmost gap is a wildcard any two may fill. Blue Moon keeps all fifty-two cards on the board, its rows are thirteen cards long behind an Ace, and those Aces are the anchors rather than being absent. The two boards look alike at a glance and the opening decisions are not the same.

Its other close relative in this catalogue is Paganini, David Parlett's two-deck version, where the Aces stay in the grid and may be moved to a leftmost slot whenever the player chooses — and where there is no redeal at all.

One honest note on difficulty. No published win rate for Blue Moon that we can find carries a method or a sample size, so this page quotes none. Structurally the two redeals are what make the family playable at all: without them a single badly placed King can end a game in a dozen moves.