Stellar encounter puzzle

[Mart10]

I dont really get the puzzle, can anybody explain it better than the game does?

[Quintalian]

You need to pick one empty square. The correct square lies on the intersection of two diagonal lines of squares which don't have any star squares on them.

[Mozzarella]

Thank you!

[EmilyApricot]

Quintalian. Thanks. What had me was the comets mentioned are not on the map. You have to imagine them crossing the map diagonally without touching any stars.

[Sajiro]

this puzzle got me stuck cause .... that's not what diagonals means