How did Explorers Navigate?
Part I – Finding the North Star
Out of all the starts in the sky, there is one who’s position remains fixed in the night sky while
the others seem to rotate around it. That is the North Star. This, and the other stars, were
crucial to the explorers being able to navigate the globe. The sun, always rising in the East and
setting in the west, also aided the early explorers. Let’s see how they did it!
Finding the North Star
If you are using the North Star to help navigate, the first thing you have to do is to locate it!
One of the easiest constellations in the sky to locate is the Big Dipper (Ursa Major, also known
as the Big Bear) Use the two stars at the very tip of the spoon and follow that line straight to
the handle of the Little Dipper (Ursa Minor or the Little Bear) and that very bright star on the
end will be the North Star.
Star Swirls
During the night hours, stars appear to travel across the sky in a circular pattern. This is caused
by the Earth spinning on its axis. The closer the stars are to the North Star, the smaller the
circles appear to be. The farther away the stars are, the larger their arc appears to be.
Because the North Star shines directly over the Earth’s spinning axis, it barely appears to move.
See the photo below taken on a camera with the shutter left open for a long period of time.
Because the North Star appears to stay fixed, it is used to take absolute measurements of
latitude. The closer you get to the North Pole, the higher in the night sky the North Star
appears to be. When you reach the North Pole, the star is directly above you.
In order for early travelers to know where they were going, they needed to know their latitude
and longitude. They also needed to know their compass direction. See the lines of latitude
and longitude on the globe below. These help explorers chart their course. Try to map a few
coordinates yourself.
Latitude lines run across and Longitude Lines run up and down.
If you are located at latitude 30N and 90E, where are you? Place an X on the coordinates.
If you are at 60S and 60W, where are you? Circle it.
If you are an explorer at 30N and 70W, and you are travelling to 60 N. and 0, plot that course.
So how does this help? It just so happens that the elevation of the North Star is equal to your
latitude on the map. Measuring the elevation is fairly easy to do with a tool called a Sextant. It
can be used to measure either the angle of the sun or the stars.
Making your own Sextant
Now you get to be an explorer and learn how to navigate the seas with your very own sextant.
What you will Need:
Protractor
Tape
A fishing sinker
A straw
Fishing line
Paper
Here is a photo of an actual sextant.
Here are the steps to make your sextant
Step One – Use a protractor with a small hole in the bottom center. If yours doesn’t have one
in it already, make one. (see diagram below)
Step two – Tie your fishing weight to the fishing line and tie the other end of the line through
the hole in your protractor. MAKE SURE YOU TIE THE STRING WITH THE TIE ON THE BOTTOM
PART OF THE PROTRACTOR. If your tie is towards the inside of the protractor, you won’t get an
accurate reading. (see below)
Step 3 – Turn the protractor upside down and tape a straw across the top. You will be looking
through the straw. If it helps, cut a hole in the piece of paper and push it onto the end of the
straw that you will look through to block outside light.
How to Use your Sextant
To find the angle of elevation of objects, look through your straw and locate the object that you
are looking for. Stop the weight from swinging. When it is still, press the string tight to your
protractor and read the angle. Take the number on the protractor and subtract it from 90. If
your protractor reads 80, you do the following math: 90 – 80 = 10.
How to Measure your Latitude
On a clear night, try to locate the North Star using the information that we have given you.
Look at it through the straw. Use the same process that you used to locate the latitude of
objects to measure your latitude. Stop the weight from swinging. Press the string to the
protractor and look at the number. Subtract that number from 90 and you should have your
latitude!