Space Exploration: Above the Green Veil

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The night sky is never completely black. Even when the moon is down, the stars and nebulae give off some light. And that small glow is equalled by a chilly, luminous layer far out in space which surrounds the earth like a diaphanous green veil.

Scientists have been studying this "airglow" layer for more than 40 years, and astronomers were cursing it long before that. Its faint green luminescence, which is probably caused by the recombination of irradiated oxygen atoms, masks dim but fascinating stars from earthbound telescopes. And not until men learned how to climb above that shimmering stratum in spacecraft could observers be sure of its altitude and thickness.

Astronauts John Glenn and Scott Carpenter both looked down on the airglow layer from their soaring Mercury capsules and found it as bright from that vantage point as the earth under a quarter moon. Then, last May, Gordon Cooper took a special camera aloft with him and photographed the airglow as he passed over Australia on his 16th orbit. With color film twice as fast as anything available commercially, he shot a sharply defined green band 16 miles thick, distinct from the blue-white earth some 65 miles below. "It must have been a tremendous experience, seeing this wedding ring sticking up all around," says Physicist Edward P. Ney, who prepared the experiment along with two University of Minnesota colleagues.

Though what Cooper saw in the green veil was no surprise to scientists, the astronaut did manage to jolt them with another discovery. As he passed over South America, Cooper caught a glimpse of a thin, barely visible rust-colored layer roughly 70 miles higher than the green stratum he had been searching for. His sighting confirmed an earlier report by Astronaut Wally Schirra, and scientists now suspect the green veil may be topped by a red one made up of photochemically stimulated atomic oxygen.