How to See Where You Can't Be


Our knowledge about the infrared part of the electromagnetic spectrum resulted from Sir WilliamHerschel s experiments in 1800. He measured the temperature of the colors in the visible spectrum. Temperatures in the blue range were cooler while temperatures in the red range were warmer. A thermometer placed just outside the red range indicated temperatures above those of red light. The term infrared was given to these invisible wavelengths. Passive remote sensing devices use infrared wavelengths to locate and measure naturally available energy from invisible objects.

National Science Education Standards Addressed

  • Abilities of TECHNOLOGICAL DESIGN/Understanding about SCIENCE and TECHNOLOGY
  • Science and technology in LOCAL, NATIONAL, and GLOBAL challenges

Materials Needed

  • Shoe box (or copy paper box)
  • Equilateral glass prism
  • 4 – Alcohol thermometers
  • Roll of black electrical tape (or black paint)
  • Clear packing tape
  • 2 – 4" x 4" x 2" Wooden blocks (or rocks)
  • White poster board


Place the thermometers in the shade and record the temperature. Cover the inside bottom of thebox with white paper. Place the wooden blocks directly under one end of the box. Hold the prism on the top of the raised end of the box. Rotate it until the spectrum appears clearly on the bottom of the box. Tape the prism into place. Cover the bulb on each thermometer with the black electrical tape. Check and record the temperature of the thermometers laying in the shade. Place the thermometers at the front end of each color of the spectrum. The first bulb should be placed in blue, the second in the yellow, the third in the red and the fourth in an area slightly beyond the red light of the spectrum. Check and record the temperature of the thermometers at 1 minute intervals up to 10 minutes. Take the last reading just before the spectrum moves significantly, even if it is under 10 minutes.


  • How different are the temperature readings for each thermometer? Construct a chart and a diagramwhich illustrates the temperature differentials obtained during the experiment. Which colors show the greatest temperature differences? Why?
  • How would the time of day the experiment was conducted affect the results? What is the optimal timeof day to conduct the experiments? What effect would the size of the box have on the experiment?
  • How can you assure larger bands for the wavelengths? How would this affect the experimental results?
  • What is passive remote sensing? Why is the difference in temperature important in remote sensing?


  • Design an experiment using passive remote sensing to determine how conifers, deciduous trees, water,ground, houses, sky, clouds, and people appear in varying wavelengths of light. What role do temperature and remote sensing play in studying the landscape at a recovery site at Mr. St. Helens shortly after the volcanic event? Share your findings with the class using graphics and demonstrations.
  • Combine with another group to test your viewing prowess. Have the other team set up a scene in whichyou are to find five hidden objects. You and your team are to find as many objects as possible. Time yourself to see how long it takes to locate the items. Now, it is your team s turn to hide five objects. Time the other team to see how long it takes them to locate your items. Which items were most difficult to find? Why? Were all the items found? Why or why not? Try this with other teams from your class.
  • Use the internet to locate additional information about passive remote sensing. Design a device thatwould assist you in your remote sensing endeavors. Construct the device and use it in a remote sensing activity. Provide pictural data detailing your results. Share your information with the rest of the class by developing a television infomercial designed to sell your new product.
  • Obtain a roll of near infrared film for a 35 mm camera. You may obtain the print film from specialtycamera supply stores. Take pictures of these areas with standard color film, black and white film, and infrared film. Prepare a comparative photo montage of your results for display.