ALMOST EVERYANCIENT CULTURE recognized the Sun as the giver of life and primary power behind events here on Earth. The Sun is the center of our solar system, our local star. It has no permanent features because it is gaseous-mainly incandescent hydrogen. The temperature of the Sun's visible yellow disk-the photosphere-is about 9,900oP (5,500°C).Over the photosphere, there are layers of hotter gas-the chromosphere and corona. The thin gas in the corona is at about a million degrees. By using spectroscopic analysis (pp.30-31), scientists know that the Sun, like most stars (pp.60-61), is made up mostly of hydrogen. In its core, the hydrogen nuclei are so compressed that they eventually fuse into helium. This is the same thing that happens in a hydrogen atomic bomb. Every minute, the Sun converts 240 million metric tons of mass into energy. Albert Einstein's famous formula, E=mc2, shows how mass and energy are mutually interchangeable (p.63), helping scientists to understand the source of the Sun's energy.

EVEN THOUGH THE SUN is more than 93 million miles (149 million km) from Earth, its rays are still bright enough to damage the eyes permanently. The Sun should never be viewed directly and certainly not through a telescope or binoculars. Galileo went blind looking at the Sun. This astronomer is at the Kitt Peak National Observatory in Arizona. Two mirrors at the top of the solar telescope tower reflect the Sun's image down a tube to the mirror below. Inside the tube there is a vacuum. This prevents distortion that would be caused by the air in the tower.

CORONAL LOOPS: Huge loops of very hot gas surge through the Sun's corona, guided by the magnetic field. These loops are about 30 times larger than Earth. This picture was taken from space. Sometimes, the corona blasts huge clouds of gas into space. If one of these coronal mass ejections reaches Earth, it may cause a magnetic storm and trigger an aurora (northern or southern lights).