GEOL 3378: Introduction to Atmospheric Science
Course instructor:
Dr. Jim Lawrence,
Dept of Geosciences,
UofH
EXERCISE #4 : MEASURING LATITUDE
Due September 27, 2002
- You will need a measuring tape and a vertical pole ( it is important
that the pole not be leaning, you can use a carpenters level to make sure).
You also could use a plumb line.
- Get a newspaper and check the time of sunrise and sunset. Having this
information you can determine the time that the sun is due south of you by
knowing the time exactly half way between sunrise and sunset.
- On SEPTEMBER 20, 21, 22 or 23 at the midday time you determined
above go out and measure the height of your pole and and the length of the
shadow and record the measurements on your answer sheet. Do it as close to
the time as possible. A few minutes off can affect the answer. Of course,
you need a sunny day so that's why I gave you 4 days to do the exercise.
Don't wait until the last day and have it be cloudy.
- Draw a diagram of parallel sun rays approaching the Earth. Have the
rays hit the Earth vertically (directly overhead) at the equator. At some
distance from the equator draw your pole sticking up vertically out of the
Earth. Notice that it is not parallel to the rays coming from the sun. Show
and explain by drawing parallel lines coming from the sun and the vertical
line of your pole sticking out of the Earth which passes through the center
of the Earth that the Inverse Tangent of the length of the shadow divided
by the height of the pole is your latitude (i.e. the tangent of the latitude
equals the length of the shadow divided by the length of the pole). Using
this relationship calculate your latitude and record it on your answer sheet.
Show all your work. Do not just write down the answer. This simple relationship
applies on September 21 and March 21 and becomes more and more inaccurate
at other dates removed from these. Why is this so?
- If you wanted to make a calculation on other dates you would need
some tables to make adjustments to your calculation. Ancient astronomers
were able to make up such tables by observing the sun year round.