CP Science 9 Sun's Radiation and Latitude Lab

INTRODUCTION: Weather Weather is the state of the atmosphere at a particular place for a short period of time. The condition of the atmosphere at any place and time is described by measuring the four basic elements of weather: temperature, moisture, air pressure, and wind. Of all the controls that are responsible for causing global variations in the weather elements, the amount of solar radiation received at any location is the most important.

Solar Radiation and the Seasons The amount of solar energy (radiation) striking the outer edge of the atmosphere is not uniform over the face of Earth at any one time, nor is it constant throughout the year at any particular place. The amount of solar radiation received at any particular place on Earth on any given day is determined by the sun's intensity and duration. Intensity is the angle at which the rays of sunlight strike a surface, whereas duration refers to the length of daylight.

Radiation Measurement The standard unit of solar radiation is the langley, equal to one calorie per square centimeter. The solar constant, or average intensity of solar radiation falling on a surface perpendicular to the solar beam at the outer edge of the atmosphere, is about 2 langleys per minute. As the radiation passes through the atmosphere, it undergoes absorption, reflection, and scattering. Therefore, at any one location, less radiation reaches Earth's surface than was originally intercepted at the upper atmosphere.

Solar Radiation and Latitude The amount of radiation striking a square meter at the outer edge of the atmosphere, and eventually Earth's surface, varies with latitude because of a changing sun angle.

PURPOSE: Determine the relationship between latitude and solar radiation intensity

MATERIALS: compass metric ruler protractor

PROCEDURE: Part 1 Copy the DATA and DATA ANALYSIS sections on a sheet of paper. On the figure provided extend the wide beam of sunlight from the sun vertically to point A on the surface. Extend the second wide beam, beginning at the sun, to the surface at point B. Notice in the figure that the sun is directly overhead (vertical) at point A and the beam of sunlight strikes the surface at a 90° angle above the horizon. Record this angle on the DATA sheet. Using a protractor, measure and record the angle between the surface and the beam of sunlight coming from the sun to point B. Measure and record the lengths of the line segments on the surface covered by the sun beam at point A and point B. Part 2 In the middle of sheet of white paper use the compass to draw a circle (Earth) with a radius of 5 cm and mark the center point with a pencil. Use the protractor and ruler to draw a line (Sun ray) from the center of the circle perpendicular to the edge of the paper. Mark the point where the line crosses the circle as 0°. See Figure 1. Use the protractor to mark a line and point on the circle 30° above the line. Mark this point 30° N. Use the protractor and ruler to draw a line from the 30° mark on the circle perpendicular to the edge of the paper. See Figure 2.

Repeat the two steps above at 60° and 90°. Use the protractor to draw a line (horizon) on the circle tangent to the 30° N point. Measure and record the angle between the Sun ray and the tangent line. Mark this angle as b on the drawing. See Figure 3. Repeat the two steps above at 0°, 60° N and 90° N, labeling the angles as a, c and d respectively. Label the points where the 0°, 30 ° N, 60° N and 90° N Sun ray lines meet the edge of the paper as w, x, y and z respectively. See Figure 4. Your drawing represents the total amount of solar radiation intercepted by each 30° segment of latitude on Earth. The lines from the edge of the paper represent the Sun's rays. With the metric ruler, measure and record the total width (mm) of incoming rays from point w to point z. Assume the total width of the incoming rays from point w to point z equals 50% of the solar radiation that is intercepted by Earth. Calculate and record what % each millimeter represents.

DATA: Part 1 Angle from point A: _____ Angle from point B: _____

Length of line segment A: _____ Length of line segment B: _____

Part 2

Angle a: _____ Angle b: _____ Angle c: _____ Angle d: _____ Width of W-Z: _____ 1 mm = _____%

DATA ANALYSIS: Part 1 Which of the two beams, A or B, is more spread out at the surface and covers a larger area? Which area, A or B, receives more langleys per minute per square centimeter on its surface?

Part 2 Using your data from part 2, #6, what percentage of the total incoming radiation is concentrated in each of the following 30o segments? 0°-30° 30°-60° 60°-90° What is the general relationship between the amount of radiation received in each 30° segment and the angle of the sun's ray (angles a, b, c, and d)? What fact about Earth creates the unequal distribution of solar energy, even though each zone represents an equal 30° segment of latitude?