One might imagine outer space to be a peaceful place - a haven from the elements, an infinite expanse of utter purity with
. . . more pellucid streams,
An ampler ether, a diviner air,
And fields invested with purpureal gleams.
But there is weather even in infinity - or phenomena, at least, which go by weather names; space has its "magnetic storms" and "solar winds".
The Sun radiates energy to space in various forms. Heat and light are the most obvious but there are also X-rays, radio waves, and the "solar wind" - a continuous stream of tiny particles that spiral outwards from the rotating star. During periods of high sunspot activity, "gusts" occur in this solar wind to give what we call a "magnetic storm".
In such cases the protection normally provided by the Earth's magnetic field is no longer quite sufficient; the extraneous energy causes satellites to wobble in their orbits, and electrical power distribution networks, radio communications and computers systems are subject to disruption.
SOHO can now tell us when events like this will happen. The Solar and Heliospheric Observatory, a project undertaken jointly by the European Space Agency and its American counterpart, NASA, was launch ed on December 2nd, 1995. It was checked out and carefully tested over the succeeding months and then switched on for routine use just five years ago this month, in April 1996.
The anomalous bursts of energy that result in a magnetic storm on Earth are associated with clusters of sunspots on the solar surface. Unfortunately, by the time these areas of high activity swing into view on the face of the rotating Sun, it is too late for preventive action; the magnetic storm has come upon us.
But SOHO provides advance warning in two ways.
From its vantage point about a million miles from Earth, SOHO can see a beam of ultraviolet rays emanating from any active solar zone sweeping like a lighthouse beam across interplanetary space on the far side of the Sun; once identified like this, it is easy to calculate when, after several days, the beam will have swung around to point in Earth's direction.
And another of SOHO's instruments, almost unbelievably, can peer right through the Sun to locate hidden sunspots and their active regions on its other side.
Warned that trouble may be on the way, the authorities responsible for satellites, power lines and other technological systems can take appropriate protective action. And the "far-side forecasts" are also useful for scheduling manned space operations, during which astronauts might otherwise be exposed to dangerous particles if the Sun was in an active mood.