Getting the blues: picturing the universe in the far ultraviolet.

If you want a snapshot of ordinary, sunlike stars, look in visible light. But if you're searching for fireworks, cast your eyes into the blue.

It's at ultraviolet wavelengths that hot, energetic stars begin to stand out from the crowd, no longer swamped by emissions from the much larger population of cooler stars similar in mass to the sun.

Although a number of Earth-orbiting telescopes have studied X-ray emissions, few have ever before viewed the cosmos in the part of the electromagnetic spectrum known as the far ultraviolet. During a recent 16-day sojourn above Earth's atmosphere as part of the Astro-2 Observatory, the Ultraviolet Imaging Telescope (UIT) did just that, capturing some 750 images of stars, supernovas, colliding galaxies, and regions of recent starbirth (SN: 4/8/95, p.213). It also recorded the first detailed ultraviolet image of the moon.

Precision pointing enabled the telescope to stare at 52 of the targets for more than 1,000 seconds each, recording radiation that can't penetrate Earth's ultraviolet-absorbing atmosphere. Because dust in galaxies also obscures ultraviolet light, the telescope can glimpse only those few massive stars that happen to lie in relatively dustfree regions.

Astronomers weren't able to develop UIT's film and see the new images until the shuttle had returned to Earth. Now, those pictures promise to shed light on the nature and timing of starbirth in a variety of galaxies. The sharpness of the pictures and their wide field of view may serve to guide follow-up observations by the Hubble Space Telescope, says UIT co-investigator Susan G. Neff of NASA's Goddard Space Flight Center in Greenbelt, Md. Hubble can zero in on selected regions of a galaxy, imaging them at longer ultraviolet wavelengths, but at considerably higher resolution, than the UIT can at far-ultraviolet wavelengths.

Team leader and UIT designer Theodore P. Stecher of Goddard, along with Neff, Robert H. Cornett of Hughes STX Corp. in Lanham, Md., and their colleagues, presented several of the new images in June at a meeting of the American Astronomical Society in Pittsburgh. The following represent a sample of those pictures.