Electromagnetic Spectrum Description

(Click on the above diagram to see a full resolution version. Adapted from W. J. Kaufmann, "Universe", [Freeman:New York].)

The "electromagnetic spectrum" is a term used to describe the entire range of light radiation, from gamma rays to radio waves. We tend to think of optical radiation as "light," but the rainbow of colors that make up optical or "visible" light is just a tiny part of a much broader range of light energy. Many of these other portions of the spectrum get totally or partially blocked by earth's atmosphere, requiring telescopes to be flown in space if we are to observe objects at these wavelengths. There are no hard boundaries or breaks in this distribution of light energy, although for convenience we assign names to various sections, as shown in the diagram above.

Ultraviolet light picks up at the blue end of the optical portion of the spectrum and continues to shorter wavelengths, eventually blending into the X-ray range. HUT's distinction is that it can operate farther into the ultraviolet (that is, to shorter wavelengths of light) than other space-borne telescopes such as the Hubble Space Telescope, a spectral range that contains much new and exciting information about the objects being observed.

Click here for a diagram that demonstrates the relative spectral ranges and sensitivities of HUT and other ultraviolet space telescopes.

If you would like to learn more about light and how it is used to learn about objects in the Universe, you may be interested in this educational Web site: What are Those Squiggly Lines? Learning from Light, put together by HUT astronomer BillBlair.