Most of the light we encounter every day is a chaotic mixture of light waves vibrating in all directions. Such a combination is known as unpolarized light. However, if the light -- or other type of electromagnetic energy -- passes through certain materials or is reflected, the waves will tend to vibrate in one direction and the light is said to be polarized. You can observe polarized light by looking through a pair of polarizing sunglasses at the brightness of the blue sky about 90 degrees from the Sun. As you rotate the glasses, the brightness of the sky will vary because the light has been polarized by being reflected in the atmosphere.
By determining the amount and direction of polarization and how these change with wavelength, one can learn about what causes the energy to become polarized. By using polarimetry (the study of polarization), scientists can learn a great deal about the object being observed and the space between the object and Earth.
The Wisconsin Ultraviolet Photo-Polarization Experiment science program is the first and most comprehensive effort to exploit the unique powers of polarimetry at wavelengths not visible on Earth. To do this, the telescope has a 50-centimeter (20-inch) mirror to reflect ultraviolet light to a spectropolarimeter, which measures the degree and direction of polarization at many different wavelengths. Before the development and flight of this experiment on the Astro-1 mission, virtually no such data existed because of the difficulty in obtaining these measurements with the degree of accuracy required for astronomical observations.
During the Astro-1 mission, the Wisconsin Ultraviolet Photo-Polarimeter Experiment team observed a variety of astronomical objects including the interstellar medium, hot stars, and active galaxies. The data gathered have allowed astronomers to refine theories and develop a better understanding of the universe. Many of these same types of objects will be observed in more detail during the Astro-2 mission to further improve our knowledge of the cosmos.
A Technical Summary of WUPPE gives more scientific details of WUPPE's capabilities.
Further information can be found on the WUPPE home page.
Portions of this text were taken from the NASA pamphlet ASTRO-2: Continuing Exploration of the Invisible Universe produced in September 1994.