Schoolyard Science #2: Celestial observations from the equator

Hi Class!  This is the next in our series of Schoolyard Science from South America.

We all have heard that the earth rotates on its axis, and that the axis of rotation is tilted relative to the axis of the earth's orbit around the sun.  Right?  Remember that?


It just so happens that on December 21st, we were exactly on the equator in the Galapagos Islands of Ecuador at exactly noon. With a clear view of the sun and horizon.  (We were on a ship.)

So we used that as a chance to check on the tilt angle of the earth.  (There are many other ways to do check, but this one is very straightforward.)

The textbooks say that the earth's north pole is tilted 23.5 degrees away from the sun on the day of the winter solstice. (See diagram above.)

At noon, with the sun at its highest point in the sky for that day, we measured the angle between the horizon and the sun.  We measured about 67.5 degrees.  (3/4 of the angle between the horizon and straight up). You don't need a sextant to estimate this value.  You can use your arm, hand and fingers and come pretty close.  See here.)

The angular width of the sun as seen from the earth is about 1/2 degree, so our measurement was really someplace between 67.0 and 68.0 degrees.

Straight overhead - angle from the horizon = angle from straight overhead.
Our numbers:  90 degrees - 67.5 degrees = 22.5 degrees.  with a half degree on either side.
Textbooks:  90 degrees - 66.5 degrees = 23.5 degrees.

So we were off by 1/2 to 1.5 degrees.  I'll take that result, given my measuring instrument was fairly primitive.

So, the science textbooks pass this test. :-)

You can try something like this at home, but you'll have to adjust for your latitude.  our being on the equator simplified the situation for us.
Cheers!

For more Schoolyard Science, see this blog post on altitude.

For more on our travels, visit here.  Thanks!