Introduction: This reflective solar cooker uses the Sun’s energy to cook marshmallows.
The target cooking area is the space where the light concentration
is greatest. Never look directly at the Sun! It could damage your
eyes. Don’t allow the cooker to reflect sunlight into your eyes.McDonald Observator

McDonald Observatory

University of Texas at Austin

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20 STARDAT E /UN I V E R SO TE A CH E R GU I D EThis reflective solar cooker uses the Sun’s energy to cook marshmal-lows. The target cooking area is the space where the light concentra-tion is greatest. Never look directly at the Sun! It could damage youreyes. Don’t allow the cooker to reflect sunlight into your eyes.MATERIALS• shoebox• aluminum foil• string• tape• straws• manila folder• marshmallows (white and chocolate, or other color)PREPARATION1. Cut slots of equal length down the short sides of the shoebox oppositeeach other. Draw a scale, beginning with zero at the top, along each slot.Then cut diagonal slits at the corners of the box for the string.2. Cut a manila folder in half along the fold. Place one half inside theshoebox, so that the folder bows into a curved, half-pipe shape resting onthe bottom of the box. Fasten with tape in this shape to the box.3. Lay a sheet of aluminum foil, shiny-side up, along the curved folder.Tape it to the box, fitting it to the folder shape.4. Cut two 20-inch lengths of string. Knot each at one end. Floss theknotted ends into slits A and B. Drape the string inside the box, andinsert the other end into slits C and D.5. Discuss the term “cook” with the class.EXPERIMENT1. Place one white marshmallow onto a straw near the end, and a coloredmarshmallow (or more, if you have several colors) on a second straw.2. Snip a slit at one end of the second straw and join the slit end to theother straw. Space the two marshmallows an inch or two apart from eachother.3. Lay the straw into the slot so that the marshmallows are near the cen-ter of the box. The straws should rest on the string at both ends.4. Pull on both strings to bring the straw to the first level from the bot-tom.5. Direct the box toward the Sun; prop it up. Allow the marshmallows tocook for a specified time.Reflective Solar CookerSAILING TO THE STARSSpace travel is a time-consuming busi-ness. It takes days just to reachthe Moon...months to reachthe closest planets...and yearsto reach the farthest planets in oursolar system. At that rate, it wouldtake many THOUSANDS of years toreach even the closest stars. RocketsCOULD go faster, but they’d need somuch fuel that they’d be too heavy tosend ANYwhere.But engineers at the Marshall SpaceFlight Center in Alabama are develop-ing a new type of propulsion that willallow a craft to literally “sail” to thestars — in a fraction of the timerequired for rockets. The first testflight could take place as soon as thenext decade.Space sails would use sunlight or apowerful laser beamed from Earth theway sailboats use the wind. Lightexerts pressure on any object itencounters.You can see this effect in acomet’s tail. Sunlight pushes tiny dustgrains away from the body of a comet,creating a tail millions of miles long.One advantage of sunlight is that it’sconstant. Although a sail-poweredcraft would start slowly, it would con-tinue to accelerate as long as light waspushing it.Marshall engineers are designing atest vehicle to travel more than 20 bil-lion miles from Earth. Early plans callfor a sail as big as 25 football fields. Itwill accelerate the attached spacecraftto speeds of almost 60 miles per SEC-OND — more than 10 times fasterthan an orbiting space shuttle.Bigger sails might cut the travel timeto the stars to centuries or evendecades — instead of millennia.STARDAT E /UN I V E R SO TE A CH E R GU I D E 216. Repeat with another set of marshmallows at a different height for thesame length of time.7. Option. After discussion, when the best height is discussed, repeat theexperiment with different cooking times.ANALYSIS1. Why is the shiny surface curved? Would this work if it were straight?2. Did the color of the marshmallow make a difference? Why?3. Did the height of the straws make a difference? Why?4. Did the student definitions of “cook” change?ANSWERS1. It is curved to focus the sunlight. A straight surface will reflect but notfocus light.2. The darker marshmallows should cook faster, since white reflectsrather than absorbs energy. (This is the reason you are cooler when youwear white clothes in the sunlight thanwhen you wear dark colors.)3. When the straws bring the marshmal-lows where the Sun’s energy is mostconcentrated, the marshmallows willcook fastest. Imagine that the reflectingsurface is part of a circular pipe(depending on the shape of your box, itmay not be perfectly circular). Thefocus is one half of the radius of thispipe. Hint: Students may notice themarshmallows are brightest when theyare near the focus.4. Most students expect “campfire”results before the experiment.NATIONAL SCIENCE EDUCATION STANDARDS• Content Standard in 5-8 EarthScience (Earth in the solar sys-tem)• Content Standard in 5-8 Scienceand Technology (Students shoulddevelop abilities of technologicaldesign)• Content Standard in 5-8 Scienceas Inquiry (Abilities necessary todo scientific inquiry, Understand-ing about scientific inquiry)012345678910Reflecting surface =aluminum foil-linedmanila folderSlit AStrawStringSlit CSlit DMarshmallowSlit B

Reflective Solar Cooker

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Reflective Solar Cooker

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