A good navigator not only studies the positions and paths of the stars, sun and moon across the sky, but also observes other clues. The colour of the water, which can indicate depth, the nature of the seabed or the proximity of a river; clouds, sky colour, indicating the presence of an island or distant shore, the scent of land carried on a breeze… Even the motion of the ship, responding to particular waves or swell patterns, can be useful. In ancient times, birds were carried on board ships, and the direction of their flight when released indicated the direction of land.

Sailors developed a variety of instruments to help with navigation. The first of these was probably the hand of the navigator himself, used to measure the approximate height of stars above the horizon. Some instruments, like the kamal, the astrolabe, the cross staff, backstaff, octant and sextant were developed to measure the angles between horizon and sun, moon and stars more accurately. Sandglasses, or hourglasses, were used to measure time.

Today we have accurate chronometers to measure time, and modern navigation also uses radio signals, satellites (GPS) or radar.