Urban dwellers who despair of ever seeing anything interestingin the night sky, take heart. This month's pairing of Jupiter and Saturn, the twin towers of our solar system, will be the most spectacular in 60 years— an in-your-face light show visible from every city on Earth.
Civilizations throughout history considered the meeting of Jupiter and Saturn, called a Great Conjunction, a highly significant event. According to one theory, the star of Bethlehem was actually a rare triple conjunction of the two planets, in which they appeared to pass each other in the sky three times. The conjunction this month is not a triple one, but it is remarkable for at least three other reasons.
First, Jupiter is close to perihelion, the point at which its oval orbit brings it closest to the sun. At perihelion, Jupiter also comes closest to Earth and receives its strongest dose of sunshine. It will not appear this bright again for nearly a decade. Second, Saturn reaches an even rarer milestone: It hasn't been this brilliant for a quarter century. Although noticeably dimmer than Jupiter, it still outshines all but two stars.
Finally, the giant planets meet in an especially desirable patch of heavenly real estate. Back in 1961 they paired in Sagittarius, which placed them low in the south, hidden behind haze, trees, and lampposts. Last time around, in 1981, the Great Conjunction location improved to Virgo, but the planets still climbed barely halfway up the sky. The present pairing is in Taurus, an ideal spot for observers in Europe or the United States. Around midnight, the duo soars high overhead, accompanied by the bright orange star Aldebaran, the menacing eye of Taurus the Bull. On November 12, a nearly full moon joins the fray.
When Jupiter comes nearest to Earth on November 26, a modest 50-power spotting scope will make it look as big as the full moon. Even a pair of binoculars will reveal Jupiter's four large satellites; they look like tiny stars that dance about the planet from day to day. Yellowish Saturn, which reaches its most proximate point a week earlier, is aligned so that its bright, icy rings appear tilted wide open. The rings stretch as wide as the disk of Jupiter, a jeweled spectacle for amateur astronomers.
Great Conjunctions have also been a boon for NASA, which has repeatedly used a gravitational lift from Jupiter to fling spacecraft to Saturn and beyond. Voyager 2
used a series of such slingshots to visit not just Saturn but also Uranus and Neptune in relatively rapid succession during the 1980s. En route, the spacecraft discovered that Jupiter's enormous cone-shaped magnetic field extends outward to the orbit of Saturn, more than 400 million miles away. The two planets touch, in a sense, each time they line up.
With the passing of the current conjunction, it will be another 20 years before Jupiter and Saturn return to an optimal configuration, and much longer still until Uranus and Neptune again fall into place. Returning for a second look at the sun's enigmatic outermost planets will require a better kind of rocket. But that is a problem for NASA's engineers. For ordinary civilians, now is the time to savor a sight that requires nothing more than a pair of eyes and a cloudless November evening.
Solar System Live (www.fourmilab.ch/solar/solar.html
) lets you plot the true positions of the planets in the solar system.
If you want to learn more about Jupiter and Saturn, drop by the extensive Views of the Solar System Web site: www.solarviews.com/eng/homepage.htm
Frustrated by light pollution that drowns out all but the brightest stars? The International Dark Sky Association (www.darksky.org
) promotes energy-efficient lighting that restores some of the beauty of the heavens.