Length of the Day & the Seasons

Solar radiation is measurable and can be used to determine the length of daylight. The number of daylight hours changes throughout the year because of the tilt of the earth.

Objectives

1. To expand the students' understanding of the seasons.
2. To learn how the length of the day changes throughout the year.

Notes to the teacher

1. The time series graphs should be for the solstices, equinoxes, and several intermediate dates (e.g., one graph per month for a year, sunny days preferably). Give each graph a number, but do not put them in a particular order.

PROCEDURE 1. Answer the questions below for each of the graphs. Write your answers on the Student Observation Sheet. What time did the sun rise? What time did the sun set? How long was the period of daylight? At what time did the Mesonet or ARM station receive the greatest amount of sunlight on this day? The least? What was the maximum solar radiation received by the sensor? The minimum? QUESTIONS 1. Which solar radiation graph represents the day with the greatest hours of sunlight?  2. In what season are the hours of daylight the longest?  3. Which solar radiation graph represents the day with the fewest hours of daylight?  4. In what season are the hours of daylight the shortest?  5. Which graph (or graphs) represents a day (or days) with an equal number of hours of daylight and of darkness?  6. What kind of information can time series data of solar radiation show us about differences between the seasons?  DISCUSSION 1. Each graph represents a different month of the year. Using the data that you have collected on your Observation Sheet, hypothesize which graph represents which month of the year. Record your hypotheses on the Observation Sheet.  2. Explain how your group determined which graphs represented days during the summer and which graphs represented days during the winter.  3. Students should record their group data on the board or overhead so that comparisons may be made.

PREREQUISITES Knowledge of Watts Basic understanding of irradiance Ability to interpret graphs   MATERIALS (Per group):  Pencil or map pencils Paper or lab notebook Oklahoma Mesonet solar radiation graphs OR ARM downwelling shortwave radiation graphs VOCABULARY Autumnal equinox  Solar radiation Summer solstice  Vernal equinox  Winter solstice     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. Create an appropriate chart or graph from collected data. Express ideas and opinions orally and in writing. Evaluate results to determine their reasonableness. Interpret line, bar and circle graphs.