The solar systems largest planet, mighty Jupiter, rises in the east at sunset during September and shines with a radiant brilliance in the constellation Pisces (the fishes) all night long. When a planet rises at sunset and sets at sunrise, it is said to be at opposition, meaning opposite the sun. At opposition, a planet is closer to earth than at any other time, and when closest it is also brightest.

An opposition of Jupiter occurs every 13 months. Because the orbits of the planets are ellipses rather than perfect circles, each opposition of Jupiter occurs at a different point in its orbit resulting in a variation in closest approach. This month Jupiter will be closer than it has been since October 1963.

Jupiter outshines Sirius, the brightest star, by a factor of four. Only the sun, moon and Venus are brighter.

Jupiter is not only bright, but it is a marvel to look at in a telescope.

Being composed almost entirely of liquid metallic hydrogen, its rapid rotation (5,000 mph at the equator) creates turbulence similar to the way tropical storms form on earth. These disturbances reveal themselves as parallel colored bands making the planet look as if it had dark rings on its surface.

The rapid rotation of Jupiter creates another interesting effect, that of a flattening of its visible disc so that rather than being perfectly round, Jupiter has an ellipsoidal shape that is quite noticeable in a small telescope. The earth is flattened because of its rotation as well, but the effect is only slight compared to Jupiter (one part in 300 for the earth versus one part in 15 for Jupiter).

One of the most compelling features of Jupiter is its collection of four large moons that travel round the planet at breakneck speed. Each of these moons are about the size of our own moon, but because of their great distance from us, they appear only as little stars, Waltzing Matildas revolving in perpetual circles shifting from night to night, first on one side of the planet and then the other.

Sometimes one or two moons are absent being temporarily in front of or behind the planet. When in front, they can be observed as tiny black dots slowly crossing Jupiters bright surface.

The discovery of Jupiters moons by Galileo in the year 1609 caused a revolution in astronomy and marked the beginning of modem science. Planetary bodies orbiting another planet revealed that the earth was not the center of the universe (as had been the popular notion throughout history up to that time) opening up avenues of inquiry and insight not previously possible.

Astronomers will be on the hilltop behind at FENCE on Saturday night, September 11th, beginning at 8:30 p.m. with telescopes set up to observe not only Jupiter and its dancing moons, but innumerable other celestial wonders that abound in the early autumn sky.

Park at the main building and walk up to the top of the hill.

All astronomy programs are free of charge. Children are welcome as always. Binoculars are a plus!

Make plans to see us on&bsp; September 11th!