# Renaissance Explorers: Making and using a Quadrant

During the renaissance, if a sailor lost sight of land he needed to have a method available to him which would help him determine his direction.  The quadrant was an instrument which allowed him to work out which latitude he was at:

We had already covered some navigational methods used by the explorers during the time of the explorers age.  These included making a chip log, a sand glass and a compass.  Collectively these are known as dead reckoning and, as methods of navigation, were very unreliable.

Often, therefore, the sailor would turn to celestial navigation.  Sailors in the past would have been very familiar with the movement of the stars across the sky at night-time.  The most important star to recognise was the Polaris or North Star:

The North Star or Polaris is known as such because of its position relative to the North Pole:

Once a sailor knew where Polaris was, he would also know where North was, and therefore South and so on.  However, simply finding the North star would not tell the explorer where he was on the globe, only which direction he was heading in.  This is where having a quadrant came in handy.

Navigators were able to calculate how far north of the equator they were by measuring the altitude of the North Star from the visible horizon. The altitude describes the height of the North Star measured as an angle.  This measurement of altitude could then be converted into the ship’s latitude position.  If Polaris is on the horizon, the quadrant will measure no angle (0 degrees latitude).  In this instance the ship would be on the equator.  If Polaris is situated at a 59 degree angle, then the ship is at 59 degrees latitude or 59 degrees North.

Whilst the Tudor explorers were able to measure latitude (how far north they are away from the equator) there were not the tools to measure longitude yet (distance from the prime meridian).  This meant they could not obtain the exact position of their ship.

An additional problem arose from the quadrant reading itself.  As we would soon find out, getting an accurate reading on terra firma was hard enough, we couldn’t even imagine attempting to obtain one on a rocky ship!