Make Your Own Astrolabe

Here's your nightly math! Just 5 quick minutes of number fun for kids and parents at home. Read a cool fun fact, followed by math riddles at different levels so everyone can jump in. Your kids will love you for it.

Make Your Own Astrolabe

November 10, 2014

When you give someone directions to your house, you might tell them your relative location first, such as, “We live southwest of the post office.” After that, you’d most likely give them your street address. But what if you wanted to be even more exact? You could give them your absolute location: the latitude and longitude of your home! Instead of 1234 Main Street, it would look like this:

38°53’23”N, 77°00’27”

 On second thought, maybe you should just give them your address!

It’s not nearly as complicated as it seems, though. Learning about longitude and latitude is a cool way to see how math and geography intersect, just like streets on a map.

360 Degree of Separation

Take a look at a globe or a photo of the earth. What shape is it? It’s a sphere. Thousands of years ago, the ancient Babylonians determined you could divide any circle or sphere into 360 degrees. Early geographers divided the earth into sections by degrees. Knowing that the furthest point at the right or left side of a sphere is 90 degrees from the top, and that there are 180 degrees between any two sides of a circle or sphere, geographers determined that the north and south poles were 180 degrees apart from each other and that both poles were 90 degrees from the equator.

Longitude and Latitude

Using these calculations, lines of latitude and longitude were created as a way to identify any location on the earth, whether on land or sea. The lines that circle the globe from east to west measure latitude, while the lines that circle the globe from north to south measure longitude.

Latitude and longitude make up a grid of intersecting lines on a globe that help us explain exactly where we are anywhere on Earth. The line at 0 degree latitude is the equator, an imaginary line that is equidistant from the North and South poles.

The line at zero degrees longitude is the prime meridian. The International Date Line is 180 degrees, or exactly opposite the prime meridian.

Find Your Address

Now, back to your very specific address! Latitude and longitude measurements are expressed in degrees. The degrees are then divided into minutes and seconds, with 60 minutes in each degree and 60 seconds in each minute. So you would read this location, as 38°53’23”N, 77°00’27”, as 38 degrees, 53 minutes, and 23 seconds north of the equator and 77 degrees, 0 minutes and 27 seconds west of the prime meridian. Want to know your absolute location? You can plug your address into the World Atlas and find the latitude and longitude of where you live.

Long ago, sailors used a mariner’s astrolabe to navigate the oceans. Unlike traveling on land, wide open bodies of water don’t have road signs to guide travelers. An astrolabe measures celestial altitude, or the height of the sun, moon or a star above the horizon. If sailors knew the height of one of these objects above the horizon, they could figure out what latitude they were located on and stay the proper course.

You can make your own simple astrolabe and use it to estimate the height (altitude) of a tree, building, or other vertical object.

Here’s what you’ll need:

  • String
  • Ruler
  • Scissors
  • Plastic protractor, with a small hole halfway along the flat edge
  • Small weight, such as a washer
  • Tape
  • Drinking straw
  • One 4″x4″ piece of cardboard or construction paper

Make an Astrolabe

Cut a 10-inch length of string and tie a knot at one end. Feed the other end of the string through the hole in the protractor until the knot catches on one side. Tie or tape the weight to the opposite end of the string.

Position the straw along the flat edge of the protractor so that one end of the straw extends several inches past the end of the protractor and tape it in place. Use a pencil to poke a hole in the center of your paper, just big enough for the straw to pass through snugly. Slide the paper onto the straw until it touches the edge of the protractor.

Make Your Own Astrolabe at Bedtime Math

Use an Astrolabe

Hold your astrolabe so that the curved side of the protractor is pointing towards the ground and the weight is hanging freely. Look through the end of the straw that sticks out and aim it at an object in the distance, such as the moon, a treetop or the roof of a house.

Hold your astrolabe steady while your partner reads where the string passes through the measurements on the protractor. Read the part of the scale that runs from 0-90.  Now subtract that number on the protractor from 90. That’s the altitude, in degrees above the horizon, of your object!

Find your way to the newest Bedtime Math geography printable activity pages for more math fun!

Images courtesy of Angie Six

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About the Author

Angie Six

Angie Six

Angie Six is the voice and chief excitement officer behind her blog, The Risky Kids . You can also find her writing for her personal blog, Just Like The Number She lives in Indianapolis with her husband and two children, who often teach her a thing or two about math instead of the other way around.

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