Star Points for September, 1997; by Curtis Roelle Action on the Ecliptic and the Harvest Moon In 1543 a Polish astronomer Mikolaj Kopernik (a.k.a. Nicholas Copernicus) published "De Revolutionibus Orbium Celestium" (On the Revolutions of the Celestial Spheres) to announce his heliocentric, or "sun-centered", theory of the solar system wherein the Sun occupies the system center as the planets revolve in orbits around it. Prior to his work the widely held view not only of main-stream astronomers, but theologians and the public at large, was that Earth occupied the privileged central position. Copernicus' theory was criticized and scorned by authorities of his day who preferred the continuation of the Earth-centered theory of the 2nd century A.D. astronomer Claudius Ptolemy in his book the "Almagest". According to Angus Armitage in "Copernicus: The Founder of Modern Astronomy" (Dorset, 1990), the religious reformer Martin Luther said of Copernicus, "The fool will turn the whole science of astronomy upside down. But as Holy Writ declares, it was the sun and not the earth that Joshua bade stand still." Today little doubt remains that Earth revolves around the sun, not the other way around. Why would anyone ever believe that the sun goes around Earth? For one thing our bodies cannot detect even the slightest motion. Our senses do not reveal that Earth is whirling around the sun at more than 18 miles per second. Also when we gaze up the sun does appear to be in motion. As Earth tours around the sun each year the apparent position of the sun in the sky changes with respect to the background stars. The sun traces a path all the way around the sky and returns to the same point one year later. This celestial path among the stars is called the "ecliptic". If you imagine projecting Earth's equator so that it forms a ring around the sky you would discover that the ecliptic band is inclined to the equator by 23.5 degrees. This month the Sun will be located at one of the two points where the ecliptic and equator intersect. When the sun is at either of these points called the "equinoxes" it is located directly above the Earth's equator. The Autumnal (or Fall) Equinox heralding the first day of Fall in the northern hemisphere occurs this year on 22 September at 7:55 p.m. EDT. The planets also follow the ecliptic, more-or-less. In the early evening sky this month Venus continues to blaze brightly in the west. Through a telescope you might detect Venus is not round but rather gibbous. Mercury and Venus are the only planets to show phases like the Moon because their orbits are located inside of the Earth's. Some 100 times fainter than Venus, reddish-amber Mars is seen low in the southwest to the upper left of Venus as twilight fades. Unfortunately, since March the brightness of Mars has greatly diminished and the planet is now situated beyond the far side of the sun. Fortunately bright Jupiter in the southeast rises higher as Venus sinks toward the western horizon. Binoculars or a small telescope will reveal Jupiter's four brightest moons. The moons are called the "Galilean" satellites because they were first announced in 1610 by the Italian astronomer Galileo Galilei. Saturn rises about the time Venus sets and by the wee hours sits high in the southeastern sky. The rings of Saturn are visible even in low power telescopes and is definitely worth the trouble of looking. Our moon's orbit in turn is inclined by some five degrees to the ecliptic. During September the orientation of the ecliptic relative to the horizon causes the Moon to rise only 20 minutes or so later each night so that there is prolonged moonlight in the early evening for a period of several days. For this reason the Full Moon of September is called the "Harvest Moon". This year Harvest Moon falls on 16 September. On the same day the Moon will be at "perigee", the closest point in its orbit about Earth. Thus, the 1997 Harvest Moon may appear even larger than usual, accompanied by abnormally high ocean tides. The paths of the Moon and Saturn cross on the morning of September 18. Since Saturn is more than 3,000 times farther away than the Moon, the Moon will simply occult, or pass in front of, the planet. This type of event called an "occultation" has nothing to do with Ouija boards. An occultation is an event where one object blocks another. Look for the Moon low in the western sky. Saturn disappears on the sunlit edge of the moon at approximately 6:57 a.m. EDT and reappears on the darkened edge around 7:42 a.m. The sun will be up for both events so binoculars or a small telescope, as well as a clear sky, may be necessary to see both objects. Rise up early before the occultation and you can find Mercury in the eastern morning sky in one of its best morning appearances of the year. At 6:15 a.m. Mercury will be about 10 degrees above the eastern horizon. After that it climbs higher but the increasing twilight of the rising sun will start to interfere. Feel free to clip this article and use it for a September tour of the exciting events occurring along this stretch of solar highway called the ecliptic.