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A glowing mystery surrounds the first American in orbit

NBC News' Jay Barbree tells the story behind John Glenn's Project Mercury spaceflight in 1962 ... and behind the mysterious "fireflies" he saw while he orbited the earth.

All was right for John Glenn and his Mercury spacecraft, Friendship 7. The two rocketed into orbit as one, and after crossing Africa, Glenn became the first American to witness a sunset from space.

“This moment of twilight is simply beautiful,” he reported from high above the Indian Ocean. "The sky in space is very black, with a thin band of blue along the horizon.  The sun went down fast, but not quite as quickly as I expected.  For five or six minutes there was a slow but continuous reduction in light intensity, and brilliant orange-and-blue layers spread out 45 to 60 degrees on either side of the sun, tapering gradually toward the horizon.”

He offered other glowing descriptions of the planet sliding by beneath him. He spoke of the snow-white mantle covering high mountains, the rich deep green of Bahamian waters and the sculptured sands of the deserts. He peered down at volcanoes and saw avalanches, told of sun reflecting off the clouds and the highest spires of great cities.

In the blackness, each massive thunderstorm became a giant light bulb, spitting and snarling with electrical fire. Observing a string of thunderstorms, flattening out along the horizon, it seemed as if he was approaching a battlefield with guns flashing and rockets firing and bombs bursting. It was incredible.

Suspended in the blackest velvet of night, only the motors and instruments of Friendship 7 offered any sounds. The remainder of the universe had gone mute. His eyes became acclimated to the darkness, and he turned down the lights of his instrument panel.

Moving through the velvet night, Glenn began to see the stars.  They appeared first as a filmy haze, became defined as a blanket, and then he was staring at the brightest, most clearly defined celestial engines he had ever seen — the stars, in a glory until so very recently never seen by the eyes of humans.

As he quickly completed his first run through the night he could see the thinnest crease in the darkness, a fairyland breath of slivered light. The breath became a whisper. Then, swiftly growing to a riotous shout of color, the horizon was transformed magically into a vivid, glowing crescent that separated night from day.

As the sun stabbed across half of the capsule structure, the other half lay in shadow and the dim reflected light from the planet below.

Suddenly John Glenn was no longer alone.

Surrounding Friendship 7, like tiny light motes from some fable of fairyland, were thousands of tiny creatures.  Some came right to his window, and he stared in wonder at the tiny specks.  Then he saw they were frost and ice. Some were shaped like curlicues. Others were spangled and starry, like snowflakes sailing and dancing and swirling in an incredible swarm about the spacecraft.

Glenn was beside himself with awe and curiosity and fascination.  He had no idea where this stunning phenomenon had originated. “I’ll try to describe what I’m in here,” he radioed the ground. Those below in the tracking station on Canton Island snapped to.

"I’m in a big mass of thousands of very small particles that are brilliantly lit up like they’re luminescent," Glenn went on. "They are bright yellowish-green.  About the size and intensity of a firefly on a real dark night. I’ve never seen anything like it."

"Roger, Friendship Seven, this is Canton Capcom,” came an immediate answering voice.  “Can you hear any impact with the capsule?  Over.”

“Negative, negative.  They’re very slow,” Glenn responded.  “They’re not going away from me at more than maybe three or four miles an hour.”

The ground team was awestruck, but hardly more so than Glenn. Both sides did their best to determine what was going on “up and out there.”

Just as suddenly as they appeared, the shining specks vanished as Friendship 7 sped over the Pacific expanse into brighter sunlight.  But they were back on the next sunrise, and the next, illuminated by the rays of that rising ball of fire.

Solving the mystery of John Glenn’s “fireflies” would have to wait until the next American, Scott Carpenter, sailed into Earth orbit.

Carpenter, believed by many to be America’s first scientist astronaut, entered the final sunrise of his mission with a bang of his hand against the inside wall of his Mercury capsule, known as Aurora 7.

The moment he struck the wall, he was flying through a swarm of "fireflies" like the ones John Glenn saw.  Again he struck the capsule bulkhead, and more fireflies showered into view.   Scott Carpenter proved beyond a question that the mysterious fireflies originated from vapor vented from the spacecraft.  Vapor produced by the astronaut’s own body.

Scratch one space mystery.

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Excerpted from "Moon Shot: The Inside Story of America's Apollo Moon Landings," by Alan Shepard and Deke Slayton with Jay Barbree. Reprinted with permission. Published by Open Road Integrated Media, copyright 2011. "Moon Shot" is available from , , , and .