The North Star
On clear nights the North Star or guide star was used to navigate by. At the north pole the North Star is at the zenith, at the equator it is on the horizon. Along the meridian or longitude it can be seen at different angles and therefore can determine latitude. Viking captains knew the height of this star and took care that it had a certain direction in relation to the ship. At the end of the evening when the sun had risen it was used to navigate by. In the light Nordic summers one had the sun to navigate by for the whole day or at least a very large part of it, this made navigation easier.
A Viking captain who had made many voyages had built up quite a collection of markers and aids to navigate by wherever he was. He noticed that cloud cover over islands and island groups was different than it was over the open sea. This then gave the direction to the closest landfall.
Even though they lost sight of land they were not alone on the sea. During nesting sea birds showed the way to land. This was especially true of the Gannet which could be found far out to sea. In the evening the birds began flying towards land and the seafarers then knew what direction land was. The Gannet and other sea birds were good navigational aids both when one had gone off-course and when you wanted to know where land was.
One often saw seaweed in the sea and the color could tell you how long it had been there. If it was fresh with a strong odor it hadn’t been there long and you weren’t far from land.