Vikings were probably the very best sailors of their time.
They knew the tides and how to use them to take their ships where they wanted to go. They knew how to steer by the light of the stars and by the direction in which the winds blew in different parts of the world. They had one other trick to help the find their way at sea.
The secret was in the birds they always took with them when they sailed out of sight of land. If the ship’s captain wanted to know if land was not too far over horizon, one of the pigeon-like birds would be set free.
It would climb higher and higher, circling the mast. If the bird could not see land, it would give up and return to the ship.
For a better way to spot land, man would have to wait for the invention of the telescope many hundreds of years later.