Seasons: Four Times of the Year
Seasons are regularly recurring periods of the year characterized by a specific type of weather. The four seasons are winter, spring, summer, fall. During the year the length of daylight and darkness varies from day to day. The longest period of daylight occurs on the first day of summer, and the shortest on the first day of winter. In the Northern Hemisphere, summer starts on or about June 21 and winter starts on or about December 22. These dates are called summer and winter solstices, respectively. On or about March 21 (the first day of spring) and September 23 (the first day of autumn), the length of daylight and dark periods is the same. These dates are called vernal and autumnal equinoxes, respectively. (The seasons are reversed in the Southern Hemisphere, with autumn in March, winter in June, spring in September, and summer in December.)
In this project, you will learn what solar radiation is and how its intensity can be determined. You will also investigate the difference of intensity of radiation at different angles and how this changing intensity creates seasons.
Purpose: To model the concentration of energy from the Sun.
- transparent tape
- graph paper with 1/4-inch (0.63-cm) or smaller grid
- marking pen
- Tape the ruler along the side of the flashlight so that a 4-inch (10-cm) section of the ruler extends past the bulb end of the flashlight.
- Lay the graph paper on a table.
- Turn the flashlight on and hold it above the paper so that the ruler touches the edge of the paper and the flashlight shines down on the paper.
- Draw around the bright center circle of light you see on the paper (see Figure 9.1).
- Count all the squares that are at least halfway in the light. Figure 9.2 shows check marks in the counted squares.
- Calculate the estimated area covered by the light. Multiply the number of squares checked by the area of each square (area = length × width).
The lighted area depends on the light used and the size of the grid. In the example, the 21 lighted squares covered an area of 1.31 square inches (8.4 cm2).
Radiation, such as light, is energy transferred by waves. Solar radiation (radiation given off by the Sun), like that from the flashlight, contains different kinds of radiation, including infrared radiation (heat) and visible light. Visible light is used in this investigation to indicate how concentrated all the radiation from the light source is. The radiation is most direct when the surface and the direction of the radiation are perpendicular to each other, demonstrated by shining the light perpendicular to the surface of the paper. When light rays strike the surface at an angle, the same amount of light must now be spread out over a larger area. Since a greater area must share this light, every point on the surface receives fewer rays, and thus less intense light.
The same thing happens with the Sun and Earth, producing our seasons (regularly recurring periods of the year characterized by a specific type of weather). When the Sun's rays strike an area of Earth more directly (as in summer), that area receives more intense light and heat from the Sun. However, when the Sun's rays strike that same area of Earth at a greater angle (as in winter), that area receives less intense light and heat from the Sun. In this investigation, the smaller the lighted area produced by the light rays, the more concentrated or intense the radiation.