May 15, 2000. Copyright 2000. Graphic News. All rights reserved.

UNDERSTANDING THE STAR NEXT DOOR

LONDON, May 15, Graphic News: THE ANCIENT Egyptians believed that the sun-gods journeyed over their heads during the day and at sunset were towed by barge through the underworld of Osiris. For almost 5,000 years stargazers knew scarcely more than the pharaohs about the central force in the solar system Ð until the discovery of blemishes on the solar disk in the early 17th century.

Italian astronomer Galileo Galilei observed sunspots travelling across the surface of the sun in 1611 but it was not until 1896 that Norwegian eccentric Kristian Birkeland Ð who always wore a red fez to Òprotect his brain from radiationÓ Ð put forward a theory that the spectacular displays known as the aurora borealis, or northern lights, were caused by what he termed an Òelectrical corpuscular beam.Ó Birkeland was the first to suggest that something other than light was reaching Earth.

But the most decisive proof, prior to the space age, was that of German physicist Ludwig Biermann who in 1951 hypothesized that a stream of particles Ð which he termed Òsolar corpuscular radiationÓ Ð travelling at speeds of hundreds of miles per second was necessary to explain the appearance and size of the plasma tails of comets which always pointed away from the sun Ð irrespective of whether the comet was approaching or moving away from the sun.

It took a further seven years for Eugene Parker of the University of Chicago to suggest that the outer layers of the corona flowed away from the sun at a velocity very similar to BiermannÕs corpuscular radiation. This plasma flow, named the Òsolar wind,Ó was confirmed by instruments aboard the Soviet Lunik 2 and 3 spacecraft, NASAÕs Explorer 10 and the Mariner II in 1962, which detected a solar wind reaching speeds of 450 miles per second (700 km/sec).

In 1993 the twin Voyager space probes found direct evidence for the true extent of the sunÕs influence. Called the Òheliopause,Ó this is where the solar wind hits interstellar space. That collision produces intense, low-frequency radio signals that were detected by antennas on the Voyager spacecraft about 11.2 billion miles (18 billion km) away Ð more than three times the distance of the outermost planet, Pluto, from the sun.

We may have come a long way since the ancient Egyptians but our sun continues to present us with plenty of mystery.
/ENDS

Sources: NASA/Marshall Space Flight Center; Cambridge Atlas of Astronomy; The Planets, BBC; Associated Press; Reuters