Laboratory Activity: The Sun and Climate

The main concept that students learn from this lab activity is the relationship between insolation and temperature. Students also develop a connection between solar altitude and shadow length.

The main skills that students learn are:

1. the ability to visualize the relationship between the subsolar point (solar declination) and the sun's altitude above the horizon at a given location (solar altitude);
2. the ability to present, analyze and interpret data in graphical form;
3. the ability to decide what data should be recorded to answer a given question; and
   
4. the ability to use a sextant. Students also practice unit conversion, making drawings to scale, taking clear and complete field notes, and using a protractor to measure angle.

This lab involves the development of a simple conceptual model (relationship between solar angle and temperature) based on the interpretation of data. However, the model is not introduced in a quantitative way. The exercise also involves critical thinking in that students decide which data to record in an experiment to determine the relationship between solar altitude and temperature.

This exercise is designed for an introductory physical geography course taken by both majors and non-majors at San Diego City College, a community college in California. There are no math or English prerequisites for the course or for the lab, and students do not necessarily take the lecture and lab simultaneously (the lecture course must be taken before or at the same time as the lab). A geography lab at SDCC typically has approximately 25-35 students. there is one 3-hour lab per week.

Equipment required for the lab includes a sextant, a tape measure, a clock or watch, a thermometer, an atlas, graph paper, and a flagpole (somewhere on campus). In addition, students in the lab are required to have a physical geography textbook, a protractor, a calculator, a ruler, writing utensils, and a field notebook.

This activity should be done near the beginning of a physical geography course. I have presented it as the third lab exercise out of 12. Pedagogically, the reason for this is that students learn about climate early in the course, and can then make connections between climate and other geographic patterns. Logistically, I like to schedule this exercise at a time of year when the weather is unlikely to be cloudy (during the months of August-September in San Diego). Measurements of solar altitude should be taken as close to local solar noon as possible (at SDCC, the geography lab is scheduled so that it begins close to noon). At SDCC, most courses are semester-long, allowing students to take solar angle/temperature measurements over the course of a few months.

Before attempting this lab, students should know how to read and construct a graph, the meaning of "scale," how to use a simple algebraic formula, and the meaning of latitude and longitude. With the exception of algebra, all of these would have been covered in previous labs and lectures.

Some parts of this lab activity are specifically geared toward San Diego City College (e.g. the location of the flagpole, and the solar altitude curve for San Diego), but it is fairly straightforward to adopt these to other locations.

This laboratory exercise (see attached Lab Handout (Microsoft Word 1.3MB Jun25 06)) essentially involves four parts:

1. measuring and analyzing the shadow of a flagpole to determine the sun's angle above the horizon;
2. using a sextant to measure the solar altitude at the students' location, and deciding on other data to collect for a semester-long experiment relating solar altitude to temperature;
3. using solar declination to calculate solar altitude for other locations; and
4. comparing solar altitude graphs to temperature data obtained from the Web.

Before work on the lab begins, the instructor should give students a short summary of latitude and longitude, the Earth's rotation, and insolation. A recap of unit conversion is also worthwhile here. Finally, the instructor will need to demonstrate the use of the sextant.

Students begin part 1 by finding the flagpole and measuring its shadow. Students should bring all of their writing and drawing materials, including field notebooks, pencils, protractors, rulers, and calculators. Scale drawings of the flagpole can be done "in the field" and corrected if the students do not have the necessary information. They may work in groups -- typically, groups of no more than 3 are allowed.

When the students are finished with the questions about the flagpole, students begin considering the sun's altitude. It is important to force students to think about what data they are going to collect before allowing them to use the sextant. It is useful to have more than one sextant for this exercise. Again, students may work in groups of no more than three.

After the students use the sextant to determine the sun's angle, they should complete questions 9 and 10 (graphing their solar altitude measurement, error analysis, and evaluating the connection between solar altitude and the flagpole's shadow) before leaving.

If time remains, students can use the rest of the lab period to make the necessary graphs. Lab Handout (PDF) (Acrobat (PDF) 668kB Jun25 06) Lab Handout (Word) (Microsoft Word 1.3MB Jun25 06) Lab Answers and Notes (Microsoft Word 1.7MB Jun25 06) Field Notebook Handout (Microsoft Word 27kB Jun25 06)

I have tried a version of this lab before. The original version was more complicated and involved more graphing and algebraic manipulation. Students were frustrated and did not perform well on the original version of the lab. I believe this version is more straightforward.

It is also important to warn students not to look directly at the sun, and to use the proper shades on the sextant.

Other hints are covered in the "Context" section.

I assess students' success in the geography lab in general using their field notes.

In the field notes, I look for the following:

1. Does the student include notes on the methods used in lab, and do those notes include appropriate detail such that another student could repeat the exercise? This entails not only clear writing and drawing, but rational organization of the student's field notes.
2. Are all of the measurements written clearly? This includes labeling what is being measured and units of measurement.
3. Are the calculations clearly written and correct overall? Some mistakes are OK, as long as all work is shown.
4. Are the graphs clear, with labeled axes, titles, and units of measurement?
5. Are all of the questions in the lab answered? Are the answers correct? Do the answers demonstrate the student's thought process, or do they simply state an answer without reasoning?
   Students are awarded a "check" for each lab if they fulfill these requirements to an adequate degree (e.g. notes are well organized and clear, but answers to questions do not go into great detail about reasoning), a "check-plus" for an exceptional lab, and a "check-minus" for a lab that seriously lacks in one of the areas described above. Students are warned at the beginning of the semester that a "check-minus" means "see me."

For the collective assessment, 80% of the class will be able to:

1. Draw the flagpole and shadow to scale, and measure solar angle from the drawing.
2. Correctly measure solar altitude.
3. Correctly graph solar altitude in questions 9 and 11, and present graphs clearly.
4. Choose at least 3 of the appropriate pieces of data to collect for question 7.
5. Describe the relationship between temperature and solar altitude (question 14) for San Diego.
6. Qualitatively predict temperature for 72 degrees N.

This semester, I began using formal lab write-ups as well. Lab write-ups synthesized data from a series of lab exercises (or a multi-week exercise) designed to investigate a single topic. The individual assessment process for lab reports is slightly more formal than for lab notes, and involves allotments of points for sections of the report (e.g. a certain number of points for the "methods" section, etc.).