Electromagnetic spectrum
Optical moon X-ray Moon Gamma ray Moon



SPECTRAL MOONS. Most of us are used to the silvery Moon as it appears in the visible part of the spectrum to our eyes or in photographs made with optical telescopes (left). But peer at Luna in other wavelengths and it has a very different aspect. If you perceived the cosmos in x-rays, it would look rather like the ROSAT image (center). If your vision registered cosmic radiation, you would see something similar to the image from the Compton Observatory (right). By comparing data from wavelengths bands in the spectrum, astronomers are gaining new knowledge of the universe.

Similar to the inability to sing more than half an octave of a musical scale, the range of our eyes perceives only a limited portion of the electromagnetic spectrum. We are hopelessly stuck in the narrow band known as "visible light." Meanwhile, the wavlengths stretch out to the more languid infrared and radio frequencies on one side and tighten into highly energetic x-rays and gamma rays on the other. And each separate wavelength would add another dimension to our vision, were we able to see it.

The good news is that astronomers are finding ways around our visual impediment. Although optical telescopes, be they simple or sophisticated, are not much more than magnifying glasses, scientists are now looking at the cosmos through other lenses that allow them broaden their viewing bandwidth, from infrared to gamma rays. In the process, astronomers, astrophysicists and astrochemists are gaining unprecedented insights into the age, origin and ultimate fate of the universe; into the life cycle of galaxies, stars and planetary systems; and even into the wellspring of life itself.

Their most recent vision extension came in the form of the Chandra X-Ray Observatory, launched from the Columbia space shuttle on July 25. Chandra is the third of the National Aeronautics and Space Administration's planned Great Observatories. Its observing range neatly fills the gap in the spectrum between the Hubble Space Telescope, offering incomparable optical resolution, and the acute Compton Gamma Ray Observatory. When Chandra becomes fully operational, it will be the most powerful x-ray observatory available to astronomers, exceeding the resolving capability of its predecessor, ROSAT, by as much as 50 times.

After a smooth liftoff on July 23--which was delayed first by indications of a dangerous hydrogen leak and then by weather--the mission was letter perfect. The crew, headed by the first female shuttle commander, Eileen M. Collins, accomplished their mission of launching the largest payload ever carried aloft by a shuttle and made a flawless night landing at Kennedy Space Center on July 27.

Since then, Chandra has been in the hands of its controllers at Smithsonian Astrophysical Observatory in Cambridge, Mass.; they are guiding it into a high orbit away from the interference of Earth's electromagnetic field. The last burn of the satellite's boosters is scheduled for August 4. Meanwhile, the team has continued to test and check Chandra's instruments.

NASA has not quite completed its effort to provide space-based observatories that let astronomers apprehend the cosmos seamlessly in all wavelengths. The last of the Great Observatories, now bearing the dreary moniker of Space Infrared Telescope Facility (SIRTF), aims to tackle the other end of the spectrum. Present plans call for a launch in 2001.

All three existing NASA observatories bear the names of leading astronomers whose research contributed to the work the observatories do--Edwin Powell Hubble, Arthur Holly Compton and Subrahmanyan Chandrasekhar. As of yet, SIRTF doesn't have a scientific namesake. Got any ideas?