Dancing in the Light
He knew, by streamers that shot so bright,
That spirits were riding the northern light.
—Sir Walter Scott, “The Lay of the Last Minstrel,” 1802
January 7, 1997, seemed to be an ordinary day on the Sun. Photographs taken at the Mauna Kea Solar Observatory showed nothing unusual. In fact, to the eye and other visible wavelength instruments, the images showed not so much as a single sunspot. But X-ray photographs taken by the Yohkoh satellite revealed some serious trouble brewing. High above the solar surface, in the tenuous atmosphere of the Sun, invisible lines of magnetic force, like taut rubber bands, were coming undone within a cloud of heated gas. Balanced like a pencil on its point, it neither rose nor fell as magnetic forces levitated the billion-ton cloud high above the surface. Then, without much warning, powerful magnetic fields lost their anchoring and snapped into new shapes; the precarious balance between gravity and gas pressure lost.
The massive cloud launched from the Sun crossed the orbit of Mercury in less than a day. By Wednesday it had passed Venus: an expanding cloud over thirty million miles deep, spanning the space within much of the inner solar system between the Earth and Sun. At a distance of one million miles from the Earth, the leading edge of the invisible cloud finally made contact with NASA's WIND satellite at 8:00 P.M. EST on January 9. By 11:30 P.M. the particle and field monitors onboard NASA's earth-orbiting POLAR and GEOTAIL satellites told their own stories