The spectacular aurora borealis, or northern lights, is a rare event in these parts, but observers may get a hint of its glory tomorrow evening, when chemicals released from a high-flying NASA satellite mimic the colorful light show for scientific research.
The first of seven artificial auroras planned this month with the Combined Release and Radiation Effects Satellite could begin at 8:43 p.m. tomorrow high above the Caribbean, promising good visibility from the United States, Central America and most of Canada and South America.
"These clouds will show up as bright patches in the night sky," said Jerry Berg, spokesman at NASA's Marshall Space Flight Center in Alabama. Colored red, green or purple and lasting from five to 15 minutes, they will be "about the size of a full moon and nearly as bright."
The experiments are designed to study the way real auroras occur, a complex dance of charged solar particles and Earth's magnetic field that can disrupt high-frequency communications, damage power lines and hurt sensitive electronics on spacecraft, as well as paint the sky in brilliant hues.
Viewers are advised to look in the southern sky, at elevations between 10 degrees and 50 degrees above the horizon. And to increase the aurora's visibility, they should seek viewing locations away from city lights and haze.
Opportunities for the other releases occur between Saturday and Jan. 25, depending on conditions in the magnetosphere, the invisible shield formed by Earth's powerful magnetic field that deflects the solar wind about 40,000 miles out in space.
The wind -- charged particles surging outward in all directions from the sun at 1 million miles an hour -- sweeps around the Earth into a 240,000-mile-long tail, the same force that makes a comet's tail always point away from the sun. Sometimes the solar wind finds gaps in the protective shield, at the "polar cusps" where the looping magnetic field lines of the magnetosphere dip down to the magnetic poles.
Those charged particles collide with molecules in the upper atmosphere to produce the glowing aurora, a process similar to the one that occurs in a fluorescent light. In the northern hemisphere, it's known as the aurora borealis; in the southern hemisphere, the aurora australis.
"At times, the particles . . . make only weak, barely visible auroras," said Dr. David Reasoner, NASA project scientist at the Marshall center. "At other times, they pour out like a heavy downpour, making very bright auroras or an auroral storm."
That strange unpredictability is still a puzzle to scientists, and they hope the CRRES project will shed light on the process.
A joint effort between the National Aeronautics and Space Administration and the Air Force, the $190 million CRRES satellite was launched July 25 into a highly elliptical orbit that ranges between 220 miles high and 22,370 miles high. It carries 24 canisters containing barium or lithium vapor that can be opened by remote control.
As the satellite changes altitude, scientists can choose the height and location of the seven releases, including three of barium -- which glows green and purple -- and four of lithium, producing a red glow.
Tomorrow's release is scheduled to be nearly 4 pounds of barium vapor, at a height of 9,300 miles and lasting about 15 minutes. The largest release features 24 pounds of barium and could occur as early as Jan. 13 at 1:55 a.m.
The releases will range from 3,800 miles to 21,000 miles high, over an area ranging from Brazil to the south and the Caribbean to the north, and from the eastern tip of South America to southeast of Hawaii in the Pacific Ocean.
"There were two previous releases from CRRES in September," Mr. Berg said. "But they weren't as visible over a large area as these should be." Another half-dozen releases are scheduled for July and August, but they will be at lower altitudes that minimize visible aurora effects.
NASA officials say the experiments will "have no adverse environmental effects."
The space agency has lined up an extensive network to monitor the releases, involving 30 scientists from the United States, Germany, Canada and Argentina. They will be studying the auroras from the ground and in aircraft with special instruments.
The seven artificial auroras could occur during the following "windows" of opportunity:
Date .. Time
Jan. 10 8:43 p.m.
Jan. 12 9:18 to 9:58 p.m.
Jan. 13 1:55 to 3:44 a.m.
Jan. 14 10:32 to 11:12 p.m.
Jan. 15 12:37 a.m.
Jan. 15 3:13 to 4:58 a.m.
Jan. 15 10:56 p.m. to 12:40 a.m.
Jan. 17 7:28 to 9:28 p.m.
Jan. 18 12:01 to 1:55 a.m.
Jan. 19 8:42 to 9:21 p.m.
Jan. 19 10:45 p.m.
Jan. 19 11:55 p.m. to 3:08 a.m.
Jan. 20 3:50 a.m.
Jan. 21 11:59 p.m.
Jan. 22 1:09 to 4:22 a.m.
Jan. 23 12:52 a.m.
Jan. 24 4:15 to 5:36 a.m.
Jan. 25 3:13 to 3:43 a.m.