SCORE:

## How to play

This is an example of a finished Spiral Galaxy puzzle. The aim is to divide the grid in to areas that have rotational symmetry (of order 2) centred around the galaxy centers marked by a dot.
Each cell must be in exactly one galaxy, and each region can only have one galaxy center.
This is an example of a spiral galaxy starting grid. We have been given our galaxy centers, and a completely blank grid.
The first step with a starting spiral galaxy puzzle is to mark out the center cells for each galaxy. You will notice that there are 3 possible placings for each galaxy center,
1. The galaxy center is in the middle of a cell. In this case we can only mark that cell as belonging to that galaxy - we can make any conclusions (yet) about which surrounding cells might be in that galaxy.
2. The galaxy center is straddling two cells. In this case we know that both these cells make up that galaxy 'core'
3. The galaxy center is straddling four cells. In this case we know that all four cells make up that galaxy 'core'.
The first thing we will do is to mark out all of these galaxy centers. We do this by clicking/tapping on the grid lines.
This is what our grid looks like after marking out all of the galaxy centers. The next thing we will do is to mark all of the galaxy centers that can't be expanded any further.
As an example, look at the 2x2 galaxy in the top right. There's no way for this galaxy to be expanded any further - doing so would mean placing a cell to the right or above the grid.
We will mark the galaxies by turning the galaxy center completely black - we do this by clicking/tapping on the galaxy center.
We know that every cell must be in one galaxy. Our next step is to look for cells where only one galaxy can 'reach' that cell.
The two highlighted cells down the left side can only be part of one galaxy (we have already decided that the galaxies above and below can't be expanded any more). When marking out the cells for each galaxy, remember that you will also need to mark the cell that is rotationally opposite.
Cell A isn't quite so obvious, but there is also only one galaxy that can 'reach' cell A. Can you spot which one it is?
I have now highlighted another three cells which are 'reachable' by only one galaxy.
Can you spot them?
We have now reached this point, and you have learned all of the techniques you need to solve Spiral Galaxy puzzles.
Spiral Galaxy puzzles get harder as they get bigger, so why not try a small puzzle today!