Of course, informal observations by individual astronauts are one thing, but more precise measurements are continually being made from space: space shuttle cameras have documented damage to citrus trees in Florida and in rain forests along the Amazon. More sophisticated sensors have measured atmospheric carbon monoxide levels, allowing scientists to study the environmental effects of city emissions and land-clearing fires.
Most of the Earth’s surface is covered with water, and at first glance it all looks the same: blue. But with the right lighting conditions and a couple of orbits of practice, it’s possible to make out the intricate patterns in the oceans—eddies and spirals become visible because of the subtle differences in water color or reflectivity.
Observations and photographs by astronauts have contributed to the understanding of ocean dynamics. For example, the energy balance in the oceans is better understood as a result of discoveries of circular and spiral eddies tens of miles in diameter, of standing waves hundreds of miles long, and of spiral eddies that sometimes trail into one another for thousands of miles. If a scientist wants to study features on this scale, it’s much easier to do from orbit than from a boat.
Believe it or not, an astronaut can also see the wakes of large ships and the contrails of airplanes. The sun angle has to be just right, but when the lighting conditions are perfect, you can follow otherwise invisible oil tankers on the Persian Gulf and trace major shipping lanes through the Mediterranean Sea. Similarly, when atmospheric conditions allow contrail formation, the thousand-mile-long condensation trails let astronauts trace the major air routes across the northern Pacific Ocean.
Part of every orbit takes us to the dark side of the planet. In space, night is very, very black—but that doesn't mean there’s nothing to look at. The lights of cities sparkle; on nights when there was no moon, it was difficult for me to tell the Earth from the sky—the twinkling lights could be stars or they could be small cities. On one nighttime pass from Cuba to Nova Scotia, the entire East Coast of the United States appeared in twinkling outline.
When the moon is full, it casts an eerie light on the Earth. In its light, we see ghostly clouds and bright reflections on the water. One night, the Mississippi River flashed into view, and because of our viewing angle and orbital path, the reflected moonlight seemed to flow downstream—as if Huck Finn had tied a candle to his raft.
Of all the sights from orbit, the most spectacular may be the magnificent displays of lightning that ignite the clouds at night. On Earth, we see lightning from below the clouds; in orbit, we see it from above. Bolts of lightning are diffused by the clouds into bursting balls of light. Sometimes, when a storm extends hundreds of miles, it looks like a transcontinental brigade is tossing fireworks from cloud to cloud.
As the shuttle races the sun around the Earth, we pass from day to night and back again during a single orbit—hurtling into darkness, then bursting into daylight. The sun's appearance unleashes spectacular blue and orange bands along the horizon, a clockwork miracle that astronauts witness every 90 minutes. But I really can't describe a sunrise in orbit. The drama set against the black backdrop of space and the magic of the materializing colors can't be captured in an astronomer's equations or an astronaut's photographs.
I once heard someone (not an astronaut) suggest that it’s possible to imagine what spaceflight is like by simply extrapolating from the sensations you experience on an airplane. All you have to do, he said, is mentally raise the airplane 200 miles, mentally eliminate the air noise and the turbulence, and you get an accurate mental picture of a trip in the space shuttle.
Not true. And while it’s natural to try to liken space flight to familiar experiences, it can’t be brought “down to Earth.” The environment is different; the perspective is different. Part of the fascination with space travel is the element of the unknown—the conviction that it’s different from Earthbound experiences.