Figuring out the location of the ship without modern technology was a huge challenge for early sailors. To locate their position on a map, navigators used the system of latitude and longitude. We looked at maps and a globe, taking notice of the parallel lines running horizontally around the globe. I told them that these are called latitude lines and that the horizontal line which runs around the center of the earth is called the equator. They noticed that half of the latitude lines run from the equator to the top of the globe. I mentioned that these lines measure distances north of the equator and that the lines which run towards the bottom of the globe measure distances south of the equator. They also noticed that there are another set of lines run vertically around the globe. I told them that these are called longitude lines and that they are used to measure distances traveled east and west from a fixed point on the earth. I asked them if it was as easy to determine where to start as with the latitude lines. I then told them that it was decided that the fixed point from which longitude lines are measured is Greenwich, England.
|Illustration from National Geospatial-Intellegence Agency|
I wanted to make our own globe from a balloon and paper mache so that they could draw their own latitude and longitude lines, but then I found this neat print-out. They also noticed that the latitude and longitude lines are drawn on a map or globe form a grid. I told them that this is how a navigator was able to know his position. If he knew both his latitudinal and longitudinal position on that grid, he could figure out exactly where his ship was positioned at sea.
I told them that to find the ship’s latitude sailors used a tool called a sextant
and that the sextant measured the angle created by the noon sun, the ship, and the visible horizon or (a quadrant) the angle of Polaris, the ship and the horizon. When the measurement of this angle was found, it could be converted to degrees latitude by using a chart in the Nautical Almanac. When the measurement of this angle was found, it could be converted to degrees latitude by using a chart in the Nautical Almanac.
I thought it would be fun to make our own Quadrants and practice making measurements.
I followed the instructions and cut-out from Teach Engineering. Although this activity is for 6-8th grade, we found even our 1st grader could take readings and they had a great time being navigators. My 8th graders could in addition complete the worksheets.
Here is another explorer to add to your timeline.