FUSE What's in a Name?

Although the FUSE acronym is easy to remember, it's full name, the Far Ultraviolet Spectroscopic Explorer satellite, is quite a mouthful! But with a little explanation, this name is really quite descriptive.

Ultraviolet refers to a portion of the energy spectrum of light that is invisible to the eye, at wavelengths below the violet-blue portion of the visible spectrum. In "units" used by astronomers to measure light, visible light extends from about 3500 to 7000 Angstroms (350 to 700 nanometers, or nm), and ultraviolet light is at smaller wavelengths.

FUSE is sensitive to far ultraviolet light, in the range from about 900 to 1200 Angstroms (90 - 120 nm). This small but important region of light is largely inaccessible to other telescopes. (Hubble Space Telescope's coverage only extends down to about 1150 Angstroms, for instance.) Coatings of special materials on all of FUSE's reflecting surfaces and light detectors provide it with this special capability. Hence, FUSE complements other NASA missions,

Spectroscopic is an adjective describing spectroscopy, a technique of analyzing light to derive quantitative information about the source of the light. FUSE observes the far ultraviolet light it "sees" at high resolution, spreading the light out so that astronomers can analyze it in great detail. There are many unique spectral features in the far ultraviolet spectral range, and high resolution information is important to measure what astronomers need to see in order to learn about objects in the Universe.

The Explorer part of the title has a double meaning. Explorer-class satellites are a particular category of medium size science mission in NASA jargon. But for FUSE, the title explorer is appropriate in another way: FUSE has more than 10,000 times the sensitivity of the previous satellite that observed the far ultraviolet spectral region with high resolution, the Copernicus satellite in the mid-1970's. Where Copernicus could primarily observe stars that are visible to the unaided eye, FUSE will be able to observe much fainter and more distant stars in our Galaxy, as well as stars in nearby galaxies, the distant galaxies, and even distant quasars and so-called "active" galaxies.