Last weekend, a 19-inch aluminum sphere studded with 878 polished aluminum mirrors floated gently out of the payload bay of the Space Shuttle Discovery into orbit about 230 miles above Earth. The satellite, known as "Starshine," will circle the planet about every 90 minutes for the next six months, passing over most of the inhabited portions.

Resembling a disco ball in space, the slowly spinning spacecraft will reflect sunlight off its myriad mirrors, giving ground-based observers a view of a sparkling star-like object tracking across the deep twilight skies.

Schoolchildren in 18 countries around the world ground and polished the one-inch-wide mirrors. And now the students will be tracking Starshine's progress through the skies to see for themselves the effects of solar radiation and atmospheric drag on orbiting payloads.

Solar activity is increasing and soon will reach the maximum in the sun's 11-year cycle. As sunspots and other surface events become more frequent, greater amounts of charged particles are ejected into space. When they impact our planet, they cause the outer fringes of the atmosphere to expand, increasing the aerodynamic drag on satellites in low Earth orbit.

As a result, after about six months in orbit, the 87-pound Starshine will succumb to the atmosphere's grasp and plummet to a fiery end -- but not before its day-to-day comings and goings have been meticulously timed and recorded by hundreds of observers worldwide.

Those data will be combined and collated to give an accurate portrait of the satellite's orbit. If NASA deems the project a success, it may fly one each year over the course of one complete sunspot cycle.

One of the mirrors on Starshine was fabricated by student members of the RARE (Rocketry, Aviation, Robotics Exploration) Club at Bishop Denis J. O'Connell High School in Arlington, under the direction of science teacher Sister Dianne Mollica.

The students will spend the summer following the progress of their handiwork, recording the precise moment that the satellite passes by certain bright stars. They will use international time signals for precise timing and Global Positioning System receivers for exact geographic location.

Such measurements are important to predicting the future of the thousands of objects now in low Earth orbit. Those objects, the detritus of the space age, constitute virtually the only difference between the present night sky and the one seen by ancient Egyptians and Babylonians.

At this moment, the Air Force is tracking more than 8,000 objects in low Earth orbit. Powerful radar and visual tracking arrays enable the U.S. Space Command to keep tabs on this cosmic debris.

From the heart of Washington, an informed observer with a pair of binoculars (7 35 or 7 42 recommended for Starshine sighting) can track satellites beginning about an hour before dawn or after dusk. Satellite spotting is a great urban stargazing pastime.

Out in the suburbs, a novice observer usually can see half a dozen satellites on a clear, moonless night. At a dark sky site, well away from city lights, a novice with a basic knowledge of the sky can identify several dozen within a couple of hours.

In our area, about 40 satellites, including the Russian Mir and the International Space Station, can be seen with the naked eye at various times of the year. In addition, the 77 satellites which make up the Iridium communications network will occasionally produce brief but very strong sun glints that are sometimes bright enough to be seen in broad daylight.

Artificial Earth satellites, like everything else in the solar system except the sun, shine by reflecting sunlight. In order for a ground-based observer to see one, two conditions must be met simultaneously -- the observer must be in darkness, and the satellite passing overhead must be in direct sunlight. That's why the best viewing times are the twilight hours.

In the early days of the space age, optical tracking of satellites by amateur observers was more than just an activity at a star party. When the first primitive payloads were placed in orbit, thousands of observers around the world tracked them for the benefit of scientists.

Many schools organized "Moonwatch" programs, spacing student observers along a baseline with small telescopes to watch satellites pass by certain stars. Starshine will revive this tradition.

You can join the RARE Club and its cohorts in following the progress of Starshine. The satellite project has a Web site (http://www.azinet.com/ starshine) that will carry the latest information on the program.

If you're interested in other things whizzing around up there, check out Bright Satellites Over Washington at http://www.usno.navy.mil/pao/BRIGHTSAT.html for weekly listings of satellites visible from this area. From that page, you can link to several others and learn more about this fascinating aspect of watching the night sky.

So, if you're out in the mountains or at the beach this summer, keep an eye out for a moving, shimmering "star" tracking slowly across the sky. It's helping tomorrow's satellite engineers get a leg up on the future and providing yet another reason for Earth-bound denizens to look up.

Geoff Chester is public affairs officer at the U.S. Naval Observatory in Washington.

From Space, Good Reflections on You

The satellite STARSHINE's orbit will take it around the Earth every 90 minutes at an inclination of 51.6 degrees to the equator. It will spin at the rate of about one revolution per minute, producing a flash of sunlight from the mirrors every few seconds. Those flashes will be visible during evening twilight and before morning twilight, while the satellite is in direct sunlight and the observer on the ground is in darkness. For details on how to observe STARSHINE and contribute to the project, go to http://spacekids.hq.nasa.gov/starshine.

SOURCE: U.S. Naval Observatory

CAPTION: Starshine Project Director Gil Moore with student participants.