Sunrise and Sunset

The length of the day and the total incoming solar radiation on a clear day are directly related to the time of the year and a location's latitude. On a given clear day, stations at the same latitude should have approximately the same amount of total incoming solar radiation and the length of the day will be the same.

Objectives

1. Using a graph of Mesonet daily solar radiation, the student will be able to determine the times of sunrise and sunset and the length of the day.
2. The student will be able to describe how sunrise and sunset times change with latitude and longitude.
3. The student will be able to describe how the length of the day changes with latitude and longitude.

Notes to the teacher

1. This expansion can use real-time Mesonet data which you or the students download or it can use archived Mesonet or ARM/CART data. If the former is desired, you must also have a computer and modem and will download Mesonet data according to The Oklahoma Mesonet Software Users' Guide.

PROCEDURE 1. (Optional) Determine at least three Mesonet or ARM/CART stations which lie in a line west to east and are located at approximately the same latitude. 2. (Optional) Download time-series Mesonet or ARM/CART data from these stations for one full day, preferably when the skies are clear at all of your chosen stations. (Do not use different days for any of your stations.) 3. Graph the solar radiation at each of your chosen sites for an entire day. (You do not have to plot from midnight to midnight -- you may start at any time, as long as one full day is plotted.) You may graph all of the sites on one plot or each site on a separate plot. If you choose the latter, make sure the scale on both your X and Y axes are identical between all plots (e.g., all plots use 0 to 24 hours on the X axis and 0 to 1000 Watts per square meter on the Y axis). 4. Label the X and Y axes with the appropriate parameter name and units (e.g., Solar Radiation in Watts per Square Meter). Label each graph of solar radiation according to the Mesonet site plotted. 5. Use these graphs to answer the following questions. QUESTIONS 1. When do the solar radiation readings begin to increase from zero at each station? Are these times the same? Why or why not?  2. How long are the solar radiation data above zero for each station? Are these lengths the same? Why or why not?  3. How much solar radiation is striking each station at its peak (i.e., what is the value in Watts per square meter )? Are they different between the stations? Why or why not? 4. If you were to graph solar radiation at the same number of stations from north to south across Kansas and Oklahoma, how would your results differ in #1, #2 and #3? 5. Based on what you learned in #2, find some cities across the United States and the world that have the same length of day as your chosen sites. Predict if the weather is as warm or cold at these locations as it is at your Mesonet sites. Is the total amount of sunshine on a clear day the only determining factor in how warm or cold a location will be? Why or why not?

PREREQUISITES Understanding of latitude and longitude Ability to create and interpret graphs Knowledge of the unit Watts   MATERIALS (Per group):  Pencil Graph paper Oklahoma Mesonet solar radiation graphs World atlas Oklahoma and Kansas road maps VOCABULARY Solar radiation Watts CORE CURRICULUM SKILLS APPLIED IN THIS LESSON Use appropriate Systems International (SI) units (grams, meters, liters and degrees Celsius) to measure objects, organisms or events. Report data in an appropriate method when given an experimental procedure or information. Recognize and describe patterns. Create an appropriate graph or chart from collected data. Express ideas and opinions orally and in writing. Describe, extend and analyze a wide variety of patterns using tables, graphs and rules. Identify and extend patterns and use experiences and observations to make suppositions. Evaluate results to determine their reasonableness. Interpret line, bar and circle graphs.