The twinkling of the stars is fine for nursery rhymes and poets but much less charming for astronomers. Atmospheric turbulence causes the twinkling and more generally distorts images; left uncorrected, a state-of-the-art 10-meter telescope would achieve only the same optical resolution as an amateur's backyard scope (albeit with much greater light-gathering capacity). The 2.4-meter Hubble Space Telescope, riding expensively in orbit up above the turbulence, embodies one spectacular solution. Over the past decade, astronomers have taken great strides in applying another solution, called adaptive optics: light from a bright star is used to detect the atmospheric distortions, and a continually adjusted deformable mirror corrects for them. Though increasingly popular, the technique is so far limited to the 1 percent or less of the sky that lies close enough to a sufficiently bright star.
Astronomers have now demonstrated the advantages of a more sophisticated technique called multiconjugate adaptive optics, which uses light from several stars or lasers to produce, in effect, a three-dimensional map of the turbulence. With this method, optical corrections can be made across larger patches of sky. Multiconjugate techniques would improve the current generation of 8- and 10-meter aperture telescopes and "will be absolutely essential for the ultralarge, 100-meter telescopes now being discussed," says Robert Q. Fugate, an adaptive optics expert working at the Air Force Research Laboratory at Kirtland Air Force Base near Albuquerque.
This article was originally published with the title Three-Star Performance.