The universe of ultraviolet astronomy is strikingly different from our familiar night sky. Observed at UV wavelengths, most stars fade from view, too cool to emit such short wavelength radiation. Ultraviolet light lies between visible light and X-rays on the electromagnetic spectrum, with shorter wavelengths and higher frequency than visible light.
Most ultraviolet light is absorbed by Earth's ozone layer in the stratosphere.
That's why instruments designed to observe UV emissions must get above the atmosphere, either by using rocket-borne instruments for brief observations or by using satellites and spacecraft for longer observations. Astro-2 is scheduled to be launched from the Kennedy Space Center in Florida aboard the space shuttle Endeavour in March 1995. As the shuttle orbits 220 miles above Earth, a large contingent of scientists and engineers will guide the mission from the Spacelab Mission Operations Control Center at Marshall Space Flight Center in Huntsville, Ala., while NASA controls shuttle operations from Johnson Space Center in Houston, Texas. Each component of the observatory has a specific role. HUT conducts spectroscopy in the far ultraviolet portion of the spectrum.