Navigation is the activity of human beings sailing at sea, crossing the ocean and going from one land to the other. In the past, it was an adventure, because human geographical knowledge was limited, and the other side was an unknown world.
The courage of early sailors is well known to the world. They constantly make up for the backward navigation technology of the old era through great innovation. When the early Vikings sailed, the captain was very familiar with the sea surface and natural objects in the sea, such as birds, fish, water flow, driftwood, seaweed, water color, reflection of ice sheet, clouds, wind, etc.