engines in the centers of these strange objects.

Ultraviolet light studies have mapped the hot gas near our Sun (within about 50 light years). The high energy end of the spectrum--x-rays and gamma rays--provide scientists with information about processes they cannot reproduce here on Earth because they lack the required power. So nuclear physicists use strange stars and galaxies as a laboratory. These objects are pulsars, neutron stars, black holes, and active galaxies. Their study helps scientists better understand the behavior of matter at extremely high densities and temperatures in the presence of intense electric and magnetic fields.

Each region of the electromagnetic spectrum provides a piece of the puzzle. Using more than one region of the electromagnetic spectrum at a time gives scientists a more complete picture. For example, relatively cool objects, such as star-forming clouds of gas and dust, show up best in the radio and infrared spectral region. Hotter objects, such as stars, emit most of their energy at visible and ultraviolet wavelengths. The most energetic objects, such as supernova explosions, radiate intensely in the x-ray and gamma ray regions.

There are two main techniques for analyzing starlight. One is called spectroscopy and the other photometry. Spectroscopy spreads out the light into a spectrum for study. Photometry measures the quantity of light in specific wavelengths or by combining all wavelengths. Astronomers use many filters in their work. Filters help astronomers analyze particular components of the spectrum. For example, a red filter blocks out all visible light wavelengths except those that fall around 600 nanometers.

Unfortunately for astronomical research, Earth's atmosphere acts as a filter to block most wavelengths in the electromagnetic spectrum. (See Unit 1.) Only small portions of the spectrum actually reach the surface. (See figure 2.) More pieces of the puzzle are gathered by putting observatories at high altitudes (on mountain tops) where the air is thin and dry, and by flying instruments on planes and balloons. By far the best viewing location is outer space.

Unit Goals

  • To investigate the visible light spectrum and the near infrared and ultraviolet spectral regions.
  • To demonstrate the relationship between energy and wavelength in the electromagnetic spectrum.
Teaching Strategy

Because of the complex apparatus required to study some of the wavelengths of the electromagnetic spectrum, the visible light spectrum will be studied in the activities that follow. Several different methods for displaying the visible spectrum will be presented. Some of the demonstrations will involve sunlight, but a flood or spotlight may be substituted. For best results, some of these activities should be conducted in a room where there is good control of light.

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