Long before Mercury, Gemini, Apollo and Columbia; before Alan Shepard's suborbital flight of the Earth, Edward White's spacewalk, Neil Armstrong's first step on the moon and John Young and Robert Crippen's touchdown of the space shuttle in California's Mojave Desert, there was Chesley Bonestell, a paintbrush and, more often than not, an astonishingly prophetic imagination.

"While others argued about the possibility of rockets and spacecraft traveling to the moon and planets, Bonestell showed us what it would all look like when we got there," says Frederick C. Durant III, former assistant director of the Smithsonian's National Air and Space Museum and coauthor (with Ron Miller) of "Worlds Beyond: The Art of Chesley Bonestell."

Bonestell, the acknowledged "dean of space art" who celebrates his 98th birthday Wednesday, continues to paint nearly every day in his California studio. An exhibit of 34 of his oil paintings, dating from 1943 to 1979, is on display at the National Academy of Sciences through March 5.

Bonestell's illustrations of manned visits to Saturn and Jupiter do not differ markedly from the photographs taken by the Voyager spacecraft decades later. And even when he misses -- as he did with his moon paintings that depicted a craggy surface instead of the meteor-worn topography revealed in 1967 by the lunar probe vehicle Surveyor -- the results are no less impressive.

Meticulous detail and a demonstrated understanding of light and shadow and of mechanical perspective are the hallmarks of a Bonestell painting. Indeed, his realistic technique is such that his thin-oil paintings on heavy illustration board have been mistaken for color photographs.

Many of the paintings in the exhibit first appeared in magazines such as Life and Look during the late 1940s, when most professional engineers and scientists were yet to embrace the possibility of space flight. According to Durant, Bonestell's collaboration with science writer Willy Ley -- which resulted in the 1949 publication of "The Conquest of Space" -- "convinced a generation of post-World War II readers that space flight was possible in their lifetime."

Space painting was Bonestell's third career: He had first worked in architecture, helping on such American landmarks as San Francisco's Golden Gate Bridge and New York's Chrysler Building, and then was a special-effects artist in Hollywood.

As a "matte artist," Bonestell designed and executed realistic background paintings for such classic films as "The Hunchback of Notre Dame," "Citizen Kane" and "How Green Was My Valley." His work later appeared in such early science fiction movies as "Destination Moon," "When Worlds Collide," "War of the Worlds" and "Conquest of Space."

The skills Bonestell refined in Hollywood served him well when he turned to space art. He once explained, "As my knowledge of the technical side of the motion picture industry broadened, I realized I could apply camera angles we used in the studio and illustrate 'travel' from satellite to satellite, showing Saturn exactly as it would look."

Bonestell's marriage of science and art came full circle when he teamed with rocket pioneer Wernher von Braun for a series on the feasibility of satellite flight published in Collier's magazine in 1952. Bonestell was able to draw upon the mathematical and mechanical training he received as an aspiring architect in college to realistically illustrate von Braun's concepts.

So precise were Bonestell's renderings of von Braun's sketches of booster rockets and spacecraft that von Braun wrote in the forward to Ley and Bonestell's book "Beyond the Solar System": ". . . Chesley Bonestell's pictures . . . are far more than beautiful, ethereal paintings of Worlds Beyond. They present the most accurate portrayal of those faraway heavenly bodies that modern science can offer."

Although many of his paintings appeared in "science fiction" publications, Bonestell never felt a kinship toward the genre, says Durant. "He's much more excited about seeking the truth than fanciful imaginings of it."

Of Bonestell's catalyzing role in the formation of a national space program, Durant says, "The timing was right. It was the postwar period . . . people had expectations."

Bonestell's art serves as a reminder of how many of those expectations were met.