Early navigators used simple but ingenious tools to find their way around. The latitude hook (not pictured) of the Polynesians was a piece of split bamboo with a loop at the top; its length was aligned with the horizon and star to show when the desired latitude had been reached.    The Arabs used a more refined tool called the kamal, a rectangle of wood cut to fit the distance from the horizon to the star. It had a piece of knotted string attached, which could be held in the teeth, guaranteeing that an "arm's length" distance would remain uniform. 

Mariner’s brass quadrant. The scale spans 90 degrees and is divided into whole degrees. It was suspended from a ring and had a weighted line hanging down, which crossed one of the angle numbers marked on the ring. The quadrant shown here is a replica of the type Columbus might have used on his voyages to the New World. This one is marked off at the latitudes of Lisbon, Cabo Verde and Serra Leoa, down near the Equator where Columbus is known to have visited.

The first part of its name comes from the same Greek word that gave us "astronomy" - aster, or star - and the second derives from a Greek word meaning take, grasp, or determine. So the name can be translated as "star-finder" or "star-taker." The astrolabe is an instrument that provides a picture of how the sky looks at the observer's latitude and time.  It has moveable parts that allow it to be set for specific dates and times, and interchangeable templates that allow latitude to be set.  Besides showing the position of the sun and stars, the astrolabe can measured the altitude of the body, and the Mariner's Astrolabe eliminated all the parts that weren't necessary for this use. Like the quadrant, it had to be held vertical so that the zenith distance (degrees down from the point over the observer's head to the body) could be measured. Subtracted from 90 degrees, this gives the altitude, and for the Pole Star, this was an approximation of the observer's latitude. Astrolabe in use.For a sun sight, the astrolabe was allowed to hang freely and the alidade was adjusted so that a ray of sunlight passed through the hole in the upper vane and fell precisely on the hole in the lower vane.

The nocturnal or "night disc," was an early sea-faring navigational instrument.  The nocturnal was used as a means of calculating the latitude and the time at night for use in navigation.  First described in 1272, the nocturnal continued to be improved upon until its use faded in the late fifteenth century. The nocturnal is shaped somewhat like a hand mirror, and elaborately decorated.  The circumference was divided into twelve equal parts corresponding to the months of the year.  There was an "index" or "pointer" that pivoted from the center of the disc.  The nocturnal was placed at arm's length with the North Star Polaris visible through a hole in the center.  The pointer was aligned to the nearby star Kochab, the second brightest star in Ursa Minor, which circles the pole star Polaris.  The nocturnal’s scale would yield a correction in arcminutes, to be applied to Polaris.  The slight distance of Polaris from the true pole would otherwise result in a 50-mile error if not compensated.  This simple method of latitude determination was popular until the fifteenth century. The nocturnal could also be used to determine the time from the celestial clock that rotates around Polaris.  The month and day were set on the scales around the perimeter.

Navstar global positioning system (GPS) satellite is launched into orbit by a Delta rocket. GPS satellites continuously transmit data about the satellite’s position and the current time. Military and civilian navigators use the information gathered from several satellites to compute their own position.

Navigation from Then to Now! Fundamentals of the Global Positioning System

Kamal

Cross-staff & Back-staff Cross-staff Back-staff

Quadrant

Mariner's Astrolabe Astrolabe Astrolabe

Nocturnal

Lift-off of NavStar Delta II with GPS Satellite

Technology has Advanced! GPS: Global Positioning System

With all of this technology it is so easy to find where a place is, even a baby could do it!