The world's depleting supply of natural resources is becoming a major concern. We're challenged to find alternatives to the fossil fuels - off, coal and natural gases - which currently provide over 90 percent of our energy. Scientists state that fossil fuels will become obsolete in the very near future. Therefore, we must plan now in order to meet our future energy needs.

Solar energy is one alternative form of energy. Chances are, children will hear a lot more about it in the years that lie ahead.

In this solar energy unit, students will conduct a "hands-on" exploration of some of solar energy's practical uses. The projects - or lessons - provide easy-to-construct, workable activities for students in the intermediate grades.

Lesson 1: Our Sun a Star

Collect and display several books on the sun for students' reference. (See "For . Curriculum Integration," on next page for some suggested titles.)

Initiate a general discussion by displaying a 1/4" ball bearing and a large ball approximately 28" in diameter. Emphasize that it would take 109 ball bearings to stretch across the ball's diameter; that the sun is 1 and 0 million times as large in volume as the earth; and that its mass is one-third of a million times as great as the earth's mass.

Have students find these points of interest about the sun: What is its temperature? What are sunspots? Does the sun rotate? Research the terms spicules and flares. How long does it take for the sun's energy to reach the earth? What instruments are used to study the sun? What's a solar eclipse and why is it important to sci10' entists?

Oral and/or written reports can be shared among the students. In addition, a large bulletin board can be produced with the information gathered from the above questions and with a scale model of the sun and earth. Encourage students to gather additional facts and place them on the bulletin board, too.

Lesson 2: Simple Solar Collector Solar collectors can be made by individuals or small groups of students. A shallow cardboard box, with the' inside painted black, will be the collector. Tape several layers of newspaper around the sides and bottom, for insulation. Make holes in each end of two sides of the collector; the holes should be large enough for tubing to fit through.

Put dark, flexible tubing, about 2 meters in length, inside the collector in a back-and-forth pattern (see Figure 1). Enough tubing should be left out at both ends to be easily handled. When the tubing is in place, tape a thermometer to the bottom of the collector, between the rows of tubing. Seal the top of the collector with a transparent cover and tape the edges tightly all the way around.

Fill the tubing with water and plug both ends. Put the collector box or panel in direct sunlight. (Don't forget to measure the water's temperature before exposing the collector to sunlight.) Record temperature readings of the water every 30 minutes. Discuss the results with the class.

For an enrichment activity, ask the students to relate their experiment findings to ways of utilizing the collectors for home use. Some may want to design a house with solar collectors.

Lesson 3: Simple Solar Cooker Another method of harnessing the sun is to capture a large amount of sunlight and focus it on a small area.

Before beginning the lesson, glue aluminum foil onto a 30 x 60 cm piece of poster board. Then, ask the students to follow you outdoors with the shiny sheet of poster board. Bend the board to an approximate parabolic curve and select a student to place his or her hand in front of the curve as you aim it toward the sun. The student will need to move his or her hand back and forth until heat is noticed in a particular spot; the focal point.

Students should be able to deduce that the aluminized poster board captured the sunlight and reflected it to a particular focal point.

(IMPORTANT: Instruct students not to look directly at the reflected light on the curve! In fact, it's a good idea to provide students with sunglasses for all experiments involving direct sunlight shining on aluminum foil.)

Food can be cooked with such a curved device if these instructions are carefully followed (see Figure 2). Cut a cardboard box so that it measures 30 em x 30 cm x 45 cm. Cut out the front, leaving about 8 cm at the bottom Make a hole near the front and top of each side of the box.

With cardboard from another box, cut two circles, 30 cm in diameter. The circles need to be cut in half and the halves glued together for rigidity. On each half-circle, make a small hole, halfway between the curved side and the straight side.

Use rubber cement to glue aluminum foil (shiny side out) onto the cut half-circles. Cut another 45 cm x 45 cm square of poster board (any color). Glue aluminum foil onto the square and tape it firmly to the rounded edges of the end pieces. (The aluminum sides are inside the near-parabolic curve.)

Attach the cooker to the frame, as in Figure 2. Take the cooker outdoors to a sunny area. Adjust the solar cooker to ensure that full sunlight focuses where the food (such as a hot dog) is in place.