Monday, November 14, 2011

Geography Awareness Week 2011: Making and Using an Astrolabe

This week is Geography Awareness Week!  The powers that be have declared this year's theme to be Geography: The Adventure in Your Community.  In this spirit, I will be blogging about various geographical exercises one can do by themselves, with family, with friends, or with the community!

An astrolabe is an ancient Greek tool for measuring star positions.  It was so effective that it was used by mariners even past the time of Columbus and into the 1700s.

First off you need to create an astrolabe.  Fortunately, the University of California Berkley has a cut out design with steps on how to put together the finishing touches (or you can use a protractor).  Then one needs to know how to read the astrolabe.  The next page of the guide offers insight.  Long story short: use straw/tube to look at object, where the string crosses the scale is the height of angle in degrees.

Now that you have a working astrolabe let us do some geography and astronomy.

Finding Latitude (For Northern Hemisphere)

First off find the big dipper in the sky at night.  Make a line connect the far two stars of the cup.  Continue that line until you see a medium bright star.  That is Polaris, the north star.  Polaris is currently hovering around the north pole (not exactly but close enough) to be used as a reference for ancient scientists, mariners, and you.  Here's a helpful image to show what you are looking for.



Now that you know where Polaris is use the astrolabe to determine the degrees in height it is.  The answer you get is your latitude .  This is the number of degrees you are from the equator.  Take 90 and subtract your number and this is the number of degrees you are from the North Pole.

Charting the Stars

Pick out a star, preferably one in a constellation you can quickly find.  Determine the height in degrees with the astrolabe.  Do more measurements 30 minutes, 60 minutes, and 90 minutes later.  See how the movement is like clockwork?  That it is because the stars are not moving but the Earth is at a steady pace.  Try estimating where the stars will be in 30 minutes.  Remember, the horizon is 180 degrees and the Earth rotates 360 degrees.  Try estimating where the stars will be tomorrow at a certain time and check your results.

1 comment:

Anonymous said...

Check for misprints. "longitude"for "latitude"--wrong way subtraction.