Tale of Two Planets

Nearly two decades in coming, Jupiter and Saturn are neighbors again.

By Bob Berman|Tuesday, September 01, 1998
RELATED TAGS: SOLAR SYSTEM
As the members of the solar system roam the sky, we're treated to endless meetings between them. Look up on September 6 and watch how the moon narrowly passes Jupiter, then visits Saturn two nights later. The pair of naked-eye conjunctions are repeated on October 3 and 6.

A zodiac creeper such as Jupiter will frequently meet other planets. It has only to linger while fast-lane Venus and Mars pay a call every year or two on their speedy rounds. All manner of planetary permutations thus parade overhead for our enjoyment. One bright conjunction, however, remains elusive: the meeting of Jupiter and Saturn. This encounter, alone among the many cyclic planetary patterns noticed by ancient sky watchers, requires steadfast patience.

Enormous Jupiter, the most brilliant "star" of the midnight heavens, overtakes bright, lethargic Saturn once in 20 years. You'll have an opportunity to see this meeting only a few times in your life, so it tends to make an impression. It did, for me. As an astronomy-loving teenager in 1961, I was fascinated by Jupiter and Saturn's encounter in Sagittarius. When they next floated together, I was married, philosophically wondering where destiny would find me in another two decades. Now the Great Conjunction approaches again.

When Jupiter finally does catch lazy Saturn in the year 2000, their rendezvous will be veiled in solar glare. We'll miss the precise conjunction, but we can have some fun by observing Jupiter's approach, like a sheriff overtaking the villain. Right now it's an especially attractive pastime because we've been so planet-starved. A few stragglers lingered during the first few months of 1998, but nightfall has been utterly planet-challenged since then.

This month the deprivation ends abruptly. Jupiter reaches opposition-when it rises as the sun sets, and is closest and brightest-on September 15. Saturn arrives at that same coveted milestone almost six weeks later, on October 23. Their oppositions are closely timed because the worlds are now near enough to each other to lurk in the same part of the sky, during the same hours of night. There they'll stay throughout the rest of the year.

Both Saturn and Jupiter have glided upward, away from the blurry, horizon-hugging oppositions they've displayed in recent years. These two gas giants now look finer than they have for more than a decade.

The story gets better. Both planets orbit in elliptical paths, creating unequal oppositions, so that each year's "close approach" differs from that of the preceding one. Jupiter's 1998 opposition finds it at very nearly its closest point to the sun and Earth. The planet hasn't appeared this big (49.7 seconds of arc) since 1987.

Saturn's growth is even more dramatic. At 20 arc seconds, it's larger than it has been since 1978. Moreover, its trademark rings, which were edgewise in 1995 (greatly diminishing the planet's naked-eye brightness), have steadily assumed a more face-on tilt. They're a wondrous sight through any telescope at 60 power or higher. In this orientation, Saturn shines at magnitude zero through November-not dazzling, like Jupiter, but extremely bright and instantly obvious, even from cities. The planet is the first and only bright star to brilliant Jupiter's left. The pair are separated by 40 degrees (about two thumb-to-little-finger spans held at arm's length) and are nicely up by 10 p.m. at midmonth, and very prominent at midnight.

Factor in September and October's traditional clear skies, and, by Jove, we're suddenly in a premier observing period-the year's elite place to meet.
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