Beyond the Visible

Activity 1A: The Electromagnetic Spectrum

Objective

To identify different kinds of electromagnetic radiation and to analyze which ones reach the earth's surface.

Ask students to name other kinds of radiation besides visible light. Write all answers on a chalkboard. Give students clues until they have named all of the kinds of radiation listed on the activity sheet, and how they appear in daily life. If you've placed the Live From the Stratosphere poster on your wall, your students shouldn' have much trouble with this!

Explain that the sun and other stars produce all these forms of radiation, but that the sun is brightest at visible wavelengths. Ask students if they think we receive all of the sun's radiation? Discuss student responses.

Materials: copies of activity 1A, page 15

Procedure: Distribute the activity sheet. Read over with students. Show students that the different kinds of radiation have different looking waves. Draw a long wavelength radio wave and a short wavelength x-ray on the chalkboard. Ask students to describe the difference. Encourage students until they generate the concept of wavelength. The distance between the crests of the radio wave is greater than for x-rays. Show students that the length of each wave is given above the drawing. A radio wave has a wavelength of a kilometer. An x-ray has a wavelength of 0.000000001 centimeter. Show students how to pick out the different wave lengths on the diagram at the bottom of the page. Then let them fill in the blanks beside the diagram. (The co-packaged Space Based Astronomy contains a physical demonstration of wavelength and energy, p. 43)

For older students, this is an opportunity to review scientific notation and different units for measuring length. For younger students, the activity sheet alone should be sufficient.

Interdisciplinary Connection

Changes in the atmosphere can affect how much light (radiation) reaches the earth's surface. This page can lead to a discussion of the ozone layer, which students already know absorbs ultraviolet radiation from the sun. Students can use the graph at the bottom to predict where the ozone layer is located and can then research what may be causing changes to this part of the atmosphere. Note: In some ways, the atmospheric "window"

is opaque in an irregular way. Though the diagram at bottom of the student page is a classic, one of the advisors did his Ph.D research using 1 cm. radiation--on the ground!

Space Exploration as a Human Enterprise

Carl Sagan

There is a place with four suns in the sky--red, white, blue, and yellow; two of them are so close together that they touch, and star-stuff flows between them.
I know of a world with a million moons.
I know of a sun the size of the Earth--and made of diamond.
There are atomic nuclei a mile across that rotate thirty times a second.
There are tiny grains between the stars, with the size and atomic composition of bacteria.
There are stars leaving the Milky Way. There are immense gas clouds falling into the Milky Way.
There are turbulent plasmas writhing with X- and gamma rays and mighty stellar explosions.
There are, perhaps, places outside our universe.
The universe is vast and awesome, and for the first time we are becoming a part of it.

The Cosmic Connection, Chapter 7, reprinted by permission of the author

KAO Connection

The KAO observes infrared radiation from planets, stars, gas clouds, dust clouds and even distant galaxies. To "see" this radiation the KAO must be above that part of the atmosphere which absorbs it. Have students convert the altitude (which is given in kilometers on the student sheet) to the more commonly used feet.

The Electromagnetic Spectrum

Infrared radiation, radio waves, ultraviolet light, x-rays, and gamma rays are all different forms of electromagnetic radiation. All are waves, but the length of the waves changes with the different kinds of radiation. Human eyes can see visible wavelengths. Human skin can feel infrared radiation. Skin (especially fair skin) is also, unfortunately, an ultraviolet "radiation detector" and turns red after exposure. The diagram above shows the wavelengths of the different forms of electromagnetic radiation.

Use the wavelength scale (above) to identify each type of radiation in the diagram below right. Notice that the earth's atmosphere absorbs much of the electromagnetic spectrum. Using the diagram, estimate how high above the earth you would have to be to "see" each kind of radiation. This is the minimum elevation for a telescope that studies the universe at this particular wavelength.

KAO CORNER:

The KAO collects infrared radiation from stars, nebulae (gas and dust clouds), galaxies, comets, planets and moons. How