Groundhog Sky

By Bob Berman|Wednesday, February 01, 1995
RELATED TAGS: SOLAR SYSTEM
Groundhog Day, when those giant rodents emerge to look for their shadows, seems completely irrelevant to the science of the sky. After all, why should marmot anxieties correlate with an early spring? And what happens if some but not all groundhogs see their shadows--a likely dilemma given their wide habitat range? Do they split the difference? Three more weeks of winter instead of six?

There’s plenty of room for scientific discomfort in this whole woodchuck deal, but things look up when you burrow deeper. For starters, the February 2 date isn’t as arbitrary as it may seem.

The week of February 2 marks the astronomical midpoint of winter. Sitting halfway between the December solstice and the spring equinox, February 2 is also the date of Candlemas, the fortieth day of Christmas, first celebrated by the Byzantines some 1,500 years ago. It’s one of the cross quarter days that marked the center of the seasons in ancient times. (But a little sloppiness crept in: winter’s precise midpoint is two days later.)

As for that six more weeks of winter business--that threat was not chosen impulsively either. It’s the interval remaining until the spring equinox. (Okay, sticklers, it’s six and a half weeks.)

Calendar revelations aside, Groundhog Day’s focus is on the clarity of the sky. Unfortunately, the deck is stacked. Long-term records establish February as one of the year’s cloudiest months in nearly the entire United States. (Its antithesis is September, one of the three clearest months in most places.) Sky watchers are often reminded of this. When the brightest comet of the last quarter-century (Comet West) blazed in the winter sky in 1976, in much of the United States it was hidden behind clouds for most of its visit.

So the odds have been rigged in favor of the no-shadow/early- spring option, a short winter scenario that in most states will not be plausible until the sun becomes a red giant.

If the groundhog does manage to view his shadow this month, use that night’s clear skies for the best view of Mars since 1992. On February 12 the orange planet, half the size of Earth and devoid of woodchucks, arrives at its closest point to us. Its brilliance attracts attention immediately as it blazes halfway up the southern sky after 10 P.M.

It’s a cinch to find. Nothing else is as orange and dazzling as Mars in the midnight sky. Only the Dog Star, Sirius, much lower and blue, is a bit brighter.

Now the bad news. Because of Mars’ lopsided orbit, its biennial get-togethers with Earth occur at greatly varying distances. The current opposition is the worst of the decade. Mars may be brilliant this month, but it’s far from its riveting intensity during a great opposition, such as the ones to come in 2001 and especially 2003. Then it will blow up like a balloon to nearly twice its current size of 13.9 arc seconds and get four times brighter. The same Martian detail will emerge with half the telescopic magnification.

During February’s rare clear nights, the sky often displays remarkable transparency because of cold air’s inherent dryness. Unfortunately, wintry turbulence makes the stars twinkle as if in a fairy tale, condemning telescope owners to stare at a ball of rollicking smudginess.

But you should try anyway. And definitely check out the Red Planet with the naked eye. You never know. If agitated woodchucks can modify your heating bill, maybe Mars can deliver detail in February from 63 million miles away.
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