Planet Swarm

By Bob Berman
Dec 1, 1997 6:00 AMNov 12, 2019 6:37 AM


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Sooner or later the laws of chance force the planets into crowded, eye-catching formations, and that’s exactly what the sky has cooked up for December. Throw enough planets together and, like vegetarians at a pig roast, they’ll stand out even to the casual onlooker. Since most are bright and change position nightly, the pageant is obvious even in light-polluted cities.

The year’s earlier months gave little idea of what lay ahead. Mars peaked last March, Jupiter in August, while Venus slowly crept from behind the sun’s glare during autumn. Each world, at its own pace, has now arrived in the southwestern sky as evening dusk fades.

Last month the planets spread out in a line along the twilight horizon. Now all but one (Saturn) clump together in a 45-degree swath of sky. The rendezvous occurs in the dim constellations Sagittarius, Capricorn, and Pisces--which offer not a single bright star among them--so you can’t confuse the foreground worlds with background suns.

Tracing out the planets’ nightly shenanigans may seem as daunting as keeping track of individual ants at a picnic, but in fact it’s easy. The brightest is Venus, while the faint orange star nearly touching it (especially on December 21 and 22) is Mars. To their upper left floats the second brightest planet, Jupiter. The wallflower at this ball, Saturn, hovers much farther leftward. Mercury’s down low, just 5 degrees above the horizon as twilight ends. (It vanishes after midmonth.) Even the fainter planets pay a call: Pluto is technically above the horizon but impossibly close to the sun; Uranus is in the same binocular field as Mars on December 27 and 28; and Neptune is to Uranus’s lower right. There you have it--every planet gathered in one district, while the rest of the heavens are host to none.

Need relief from the hectic pace of holiday shopping? Pause between your car and the mall and peer low into the twilight. Every bright star to the left of the sunset is a planet. Pay special attention to the beautiful, extreme proximity of Venus and Mars in the week before Christmas. Venus appears 250 times brighter than the Red Planet because it’s now six times closer to us, twice as close to the sun, twice as large, and five times more reflective. In the shiny Christmas ornament department, Venus has it all. Mars has only the nonglittering glory of playing host to our robotic vehicle Sojourner and the orbiting Global Surveyor.

With any small telescope or even binoculars, you can see Venus’s optimally large crescent shape (on view just once every 18 months), which continues to grow bigger and more beautifully slender through mid-January. And don’t put the instrument away until you’ve checked out Jupiter and Saturn, that solitary star halfway up the southern sky.

This is not a planets-only affair: the moon, the final naked-eye solar system holdout, joins the group during the month’s first week. It hovers above Mercury on the first of December, near Venus and Mars on the second and third, just above Neptune on the third, between Jupiter and Uranus on the fourth, and just above Saturn on the eighth. The moon leaves the party for the next few weeks, but returns again on New Year’s Eve, to sit amid five planets all over again.

This is a show that airs before prime time, so observe early. After 9 p.m. only Saturn remains, and a little past midnight it, too, has set. Such a concentrated arrangement at a conveniently early time will not recur until the next century. But this year, the natural holiday lights are on display for even the youngest of Earth’s appreciative sky watchers.

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