NASA’s Galaxy Evolution Explorer (GALEX) will carry a telescope into Earth orbit that will observe a million galaxies, across 10 billion years of cosmic history, to help astronomers determine when the stars we see today had their origins.

GALEX is set to launch, no earlier than April 28, 2003, from Cape Canaveral Air Force Station, Fla. A Pegasus XL rocket, released by an L-1011 jet aircraft, will launch the satellite. The aircraft will climb to approximately 39,000 feet and release the launch vehicle and payload. The science mission will start after an initial month of in-orbit testing.

From its orbit high above Earth, the spacecraft will sweep the skies, for up to 28 months, using state-of-the-art ultraviolet detectors. Looking in the ultraviolet will single out galaxies dominated by young, hot, short-lived stars that give off a great deal of energy at that wavelength. These galaxies are actively creating stars, therefore providing a window into the history and causes of galactic star formation.

“The Galaxy Evolution Explorer is crucial to understanding how galaxies, the basic structures of our universe, form and function,” said Anne Kinney, director of astronomy and physics in the Office of Space Science, NASA Headquarters, Washington. “Its ultraviolet observations will round out the knowledge we gain from observations in infrared and other wavelengths,” she said.

Astronomers believe the universe originated approximately 13.7 billion years ago in the cataclysmic “Big Bang.” Galaxies, the basic building blocks of the universe, began to appear as the fireball of hydrogen and helium gas expanded and cooled. Recent observations suggest star formation peaked eight to 10 billion years ago. This mission is specifically designed to investigate whether this occurred and why.

The centerpiece of the satellite is a 50-centimeter-diameter (19.7-inch) telescope. It is equipped with sensors that will gather continuous images of galaxies in the ultraviolet to study their shape, brightness and size. Ultraviolet light, the type of invisible energy responsible for sunburn, is at the higher end of the electromagnetic spectrum, just above visible light in frequency, but below X-rays and gamma rays.

A device called a spectrometer will break down the light into component colors, just as a prism separates white light into a rainbow. These measurements will enable scientists to determine the distances of galaxies, and thus, their places in cosmic history. Combined with precise measurements of the ultraviolet brightness of galaxies, astronomers will be able to determine the rate at which stars are forming within those galaxies.

“This mission will provide the first comprehensive map of a universe of galaxies under construction and bring us closer to understanding how they, and our own Milky Way, were built,” said Christopher Martin, the mission’s principal investigator and an astrophysics professor at the California Institute of Technology in Pasadena.

Scientists will use data from the mission to learn when carbon, oxygen and other chemical elements were created inside blazing stars. Most of the elements found in the human body originated in stars. We are literally made of stardust. The mission will also conduct the first ultraviolet surveys of the entire sky beyond our own galaxy, including the first wide-area spectroscopic surveys. Rich in objects, from galaxies to quasars to white dwarf stars, this vast data archive will serve as a resource for the entire astronomical community.

The GALEX mission is led by the California Institute of Technology, which is also responsible for science operations and data analysis. NASA’s Jet Propulsion Laboratory, Pasadena, Calif., a division of Caltech, manages the mission and built the science instrument. The mission was developed under NASA’s Explorers Program, managed by the Goddard Space Flight Center, Greenbelt, Md. GALEX international partners include South Korea and France.

For information about the mission and NASA’s Explorers Program on the Internet, visit: