Stargazer

Everyone knows the Sun is a brilliant round ball that travels around Earth each day. Perfect and unchanging, it is made of shiny quintessence, a heavenly substance not found on Earth.

At least that's what sophisticated Europeans thought in the early 17th century when Galileo and others began studying the heavens with the newly invented telescope 400 years ago.

That view of the Sun began to crumble when Galileo and other early astronomers discovered sunspots. They seemed to be clear evidence that the Sun wasn't perfect after all. And seeing the sunspots move across the Sun's surface indicated that the Sun was rotating on its axis.

Galileo's observations, especially of Jupiter and Venus, also led him to accept Copernicus' theory that the Sun doesn't go around the Earth, but rather Earth and the other planets go around the Sun. And as mentioned in previous columns, his promotion of these heretical ideas got him in serious trouble with the ecclesiastical-governmental authorities.

Today, of course, the Sun-centered view of our solar system is universally accepted, and we have a much better understanding of the nature of our Sun.

An ordinary star, the Sun is a huge gaseous ball composed not of any exotic heavenly substance but primarily of hydrogen, the most common element in the known universe. It's heat, light, and other forms of energy come from nuclear reactions deep within its core.

At its center, the temperature is 27 million degrees whereas the temperature at the visible surface (called the photosphere) is a mere 10,000 degrees. The sunspots which so intrigued and baffled Galileo are now known to be areas of magnetic disturbance; they are darker in appearance because they are cooler.

And finally, our Sun, like all stars, is not eternal. It was born 5 billion years ago and will die in another 5 billion years. • Sky Calendar. * Mar. 7 Sun.: The Moon is at 3rd quarter. * 15 Mon.: The Moon is new. * 16 Tue.: evening: A very thin crescent Moon is to the lower right of Venus low in the west at dusk, and above the planet the next evening. * 20 Sat.: Spring (vernal) equinox, the northern hemisphere's first day of spring when day and night are (about) 12 hours long. * 20 Sat. evening: The crescent Moon grazes the Pleiades star cluster, a sight best seen in binoculars; the star Aldebaran, the "red eye of the bull," is to their upper right. * 21 Sun.: Saturn is at opposition (on the opposite side of Earth from the Sun) when it rises at sunset, is up all night, and sets at sunrise. * 23 Tue.: The Moon is at 1st quarter. * 24 Wed. evening: The gibbous Moon is to the upper right of Mars, and below the planet the next night. • Naked-eye Planets. (The Sun, Moon, and planets rise in the east and set in the west due to Earth's west-to-east rotation on its axis.) Evening: Mars is high in the east as Saturn rises an hour after sunset; Venus is visible very low in the west after sunset. Morning: Saturn, low in the west, is currently the only morning planet.