Streaking Satellites Clutter the Night Sky

While on a recent trip to a remote cabin on the bank of the frozen Yukon River, I was treated to a night sky that was free from light pollution. I stood shivering under a purple black ceiling that was crowded with a billion stars.

Suddenly, a star caught my attention by gliding steadily across the sky. It seemed to be moving very fast, and it featured a constant white light; it wasn't twinkling like the other stars. I was about to roust my cabin mates for a look at a UFO when I remembered what it was I was looking at--a manmade satellite.

My sighting was no reason to wake anybody, according to Dirk Lummerzheim, a research associate professor of aeronomy at the Geophysical Institute. "There are hundreds of them," he said of satellites orbiting about 300 miles overhead. "It's crowded with satellites.

Lummerzheim knows many by name because much of his research depends on the information sent back to Earth from satellites. He'll be plugging information from the soon-to-be launched Polar satellite into computer models in an attempt to better understand the ionosphere, the outermost shell of Earth's atmosphere.

"Satellite" is a term borrowed from astronomy to describe manmade spacecraft we put in orbit around Earth or other planets. The moon, for example, is a natural satellite orbiting Earth in an egg-shaped path.

Satellites such as the one I saw are probably military, weather, or earth-observing satellites, Lummerzheim said. These types of satellites, designed to get a sneaky or large-scale view of the world, all orbit close enough (about 300 to 600 miles up) to be seen as they reflect sunlight. These spacecraft will often seem to disappear when streaking across the night sky, a phenomenon caused when a satellite's orbit takes it behind Earth's shadow.

Unless it crashes into space debris, a satellite could orbit Earth perpetually, Lummerzheim said. Because there's no air friction in outer space, a satellite revolves around a planet because of two forces; the centrifugal force that blasted the satellite into space, and the planet's gravitational pull.

Before a satellite is launched aboard a rocket or carried on the space shuttle, scientists calculate how much thrust is needed to place a satellite into orbit at a given height above Earth. Once the satellite is slung to the proper elevation, it finds a balance between centrifugal and gravitational forces and cruises along an orbital path.

While visible satellites that eyeball Earth orbit at a relatively low elevation, satellites that carry many of our phone calls and live television programs are stationed about 22,240 miles away. At this elevation, satellites take 24 hours to orbit. This nifty feature allows scientists to "park" satellites above a spot on the equator. Although they still move, these geostationary satellites, sit in the same spot relative to the earth.

From their lofty perches, geostationary satellites can reach of one-third of Earth's surface at once, which is handy for bouncing phone signals all over the globe. If we call Germany from Alaska, for example, our signal may travel quite a distance. After dialing Germany, computers in local phone companies instantly decide whether to rout the call by ground line or satellite.

If a satellite connection is free, a computer directs the phone signal from a ground station to the satellite. If the satellite finds no direct link to Germany, it may route the signal back to a ground station somewhere else, say in Florida. From there, the signal might be directed back to a satellite, which then finds a connection at a ground station in Germany, sends the signal down and connects it by ground line to the phone of the person being called. In the seconds the connection is made, the signal has logged almost 100,000 miles.

Even though the signal is going the speed of light, the incredible mileage it's traveled sometimes results in an uncomfortable delay, in which two callers often end up talking at the same time. Combine that with the miles phone signals have covered and you've got what I call a lengthy conversation.