This handout contains the directions for Lab 4, which focuses on latitude, plus an exercise on calculating Longitude.

Lab 4 directions

We will be doing questions b-h, and of course the summary, which should discuss the questions from Lab 4 and the exercise on longitude. Question D has some modifications, the rest are done as in the lab manual.

Question D: This question is very tedious as written. Instead, we will do the following:

1) As a class we will compute the average latitude. 2) Subtract your measurement from the class average, and square it. 3) As a class we will add up our different answers found in step 2.

Then you will continue with steps 4 and 5 on your own.

Please show your work in the space for question D. Please be sure to include the numbers we calculate as a class along with a label. (i.e. Class Average = 48 degrees and Sum of the Squares = 327)

Longitude

This is just a summary of what I told you in class, so you have it for reference later.

Calculating your longitude, in principle, is a very easy thing to do, because the concept of it related to time zones, something we are very comfortable with. We all know that noon occurs at 12:00, but that noon occurs in London 5 hours sooner than it does in State College. So, if I had two watches, one set permanently to Greenwich Mean Time (GMT), and another which is set to the local time, I could determine my longitude by simply noting the time difference between the two watches. There are 15^o of longitude for every hour of time difference, so longitude = 15^o x (difference in time in hours).  For example, England is 5 hours ahead of State College, and our longitude is roughly 15x5=75 degrees West.
This same method works if you want to use night-time stars to determine your longitude, except you would need astronomical tables to tell you exactly when the ``guide'' stars should be every night.

Sounds like a piece of cake, right? Well guess again. The problem with calculating longitude in this way is that you need a watch which doesn't lose significant amounts of time. Before the 1800s, a good watch on LAND lost several minutes a day. The conditions on most sea voyages threw watches off-track completely.

On the back of this sheet, you will find a chart which shows navigational data for a voyage from Portugal to Brazil. Use the data to plot your course on the provided map. Your watch set to GMT actually loses 2 minutes per day (we'll be optimistic!)  re-determine your longitude using the ``correct'' time and plot your true course.  Note, in transporting
this figure to the web, I couldn't put the latitudes and longitudes in. The thick line horizontal line is the equator, the
thick vertical line is 0 degrees of longitude (Greenwich, England). Each line is another 15 in latitude or longitude
 
 

Feel free to use this space to do the calculations, if you wish. Just remember that
longitude = 15^o x (difference in time in hours)