It's a handy invention, the calendar. 

Next Wednesday, August 12, will be one of my favorite days of the year, the peak of the Perseid meteor shower.  On that night I love to lie flat on my back, counting the shooting stars as they streak across the night sky.  One memorable year, the whole cast of Twelfth Night lay out on the Sonoma Valley Shakespeare Festival's open air stage and on the hillside above it to greet the light show with whoops and hollers after our audience had gone home.  Another year, lying on my deck with half the sky obscured behind my house, I still counted over a hundred meteors in less than an hour.

This year the show will be a little less spectacular than it often is.  The Perseids are named for the constellation Perseus which forms the backdrop for the section of the sky from which they appear to fall.  In the northern hemisphere Perseus rises right around midnight at this time of year -- or to put it more accurately, Earth, rolling from west to east under the North Star, turns at that hour to reveal Perseus in the sky to the northeast.  This year the moon in her waning gibbous phase will appear above the horizon at about the same time, a little further to the south.  Though only half her face will be illuminated, her light will overpower the smaller and dimmer meteors, so that even under the best viewing conditions, we'll be more likely to see only fifteen to twenty shooting stars per hour, rather than the more typical sixty odd.  Even so, I'll be out there in the wee hours of Wednesday morning, looking up and digging the show.

Having a calendar makes it possible for me to make a plan like that, to know in advance what night will be the best one to dedicate to star-gazing.  The calendar is a time map on which we can chart the itineraries of our upcoming months, weeks and days.  And though we're accustomed to the standard format of stacked pages of months or days, flipping or ripping our way forward from the top of the stack to the bottom and then starting over with the next year's edition, we can arrive at a better understanding of the calendar by picturing it as a wheel, each rotation in its forward motion bringing any point on the rim through every angular degree and back to its starting position.  The arrow of time moves ever forward in one direction, but its path is always a spiral.

The calendar is a map of time, but it's also congruent with a map of space, specifically the space occupied by the solar system, and each turn of the wheel traces the path of Earth in her annual revolution around the sun.  Looking outward from the solar system in any direction we see thousands of neighboring stars, whose motions relative to us are too slow to be detectable over spans of tens of thousands of years.  Our ancestors mapped that background of apparently fixed stars with fanciful pictures that they imagined to be formed by patterns of the brighter stars, patterns that we call constellations.  Earth and all the other solar planets (now that Pluto no longer enjoys that designation) orbit our sun in the plane of the ecliptic, a virtual wheel with the sun at its hub, and the ring of twelve constellations that surround the rim of that wheel are known as the zodiac.

We can map Earth's progress on her annual revolution by observing the apparent position of the sun against the backdrop of the zodiac.  For example, each time Earth traverses the opposite side of the sun from the constellation of the Crab, she passes through an orbiting cloud of debris left behind by the Swift-Tuttle comet every 135 years since at least the first century CE, the oldest known time its passage left a record.  Our sky cushions us against thousands of tiny collisions with odd bits of comet, burning them and diffusing their ashes, but a few are big enough to burn a visible path across the sky before snuffing out.  They come at us from the direction of the constellation Perseus, and our secular calendar calls the time we pass through that cloud August.  Earth intersects nine other comet trails big enough to trigger a meteor shower each year, but the only shower to rival the Perseids in intensity are the Leonids, who drop from the direction of Leo during what we call November.

The calendar doesn't derive its order from randomly distributed annual events like meteor showers, but from two points defined completely by the dance between Earth and the sun.  Earth leans off the vertical on her axis, so that on any day of the year either the northern or southern hemisphere is pointed a little more directly into the sun, except the two days when one side faces the sun head-on and begins to turn away, the solstices -- at summer the longest day of the year on which the sun reaches its greatest height, balanced by winter's lowest ebb and longest night.

Cultures everywhere on the planet recognize those days, and wherever civilizations have arisen, they've memorialized in architecture the directions of the earliest and latest sunrises.  Those and the days of perfect balance, the equinoxes, form the cardinal points, the four spokes of the year's wheel.  Even our modern secular calendar acknowledges these days, as it does the phases of the moon, though it's mostly forgotten it ever had a connection to them.

The pagan calendar adds four more spokes to the solar wheel, the cross-quarter days, each at the midpoint between two cardinal points.  Modern pagans usually call them by their medieval Irish names -- Samhain, the witches' new year, night of the dead, remembered in All Souls' Day and Hallowe'en -- Imbolc, the stirring of spring, crudely memorialized on Groundhog Day, adopted by the Church as St Bridget's -- Bealtaine, May Eve, the night it's officially warm enough to couple outdoors -- Lughnasadh, a night of bonfires and dancing, a celebration of harvest and occasion for sporting contests.

The astrologers' wheel also starts from the cardinal points, dividing the quarters into threes and naming the twelve segments for the constellations of the zodiac.  The zero point of the astrologers' zodiac is the first degree of Aries, the precise moment of the spring equinox.  One of the arguments advanced against adherents of astrology is that the astrological signs are out of synch with the actual constellations -- when the astrologer says the sun is in Aries, the constellation directly behind the sun viewed from Earth will be Pisces or Aquarius.  I'm not here to contend that there aren't good arguments to be made against many astrologers' claims, but this particular one is founded on a misunderstanding.

The astrologers' wheel isn't a map of space, it's a map of time, a calendar, and its cardinal points are the solstices and equinoxes, not the backdrop of fixed stars.  The wheel of time and the wheel in space aren't precisely congruent nor are they fixed in relationship to each other -- there's another cycle that governs the variation in their alignment.  Earth wobbles in her rotation the same way the handle of a spinning top describes a small circle around the vertical.  The period of this cycle is slightly less than twenty-six thousand years, meaning that any of the cardinal points of the year, let's take the spring equinox as an example, arrives each year about twenty minutes earlier in Earth's revolution as measured against the backdrop of the zodiac's fixed constellations.  This results in Earth enjoying 25,772 years for each 25,771 revolutions around the sun.  It also means that the north axis of Earth's rotation doesn't always point to Polaris, the North Star, but returns to point directly at it only once in each twenty-six thousand year cycle -- the slippage should be obvious within a couple of thousand years.

And finally, that explains why the astrological and astronomic zodiacs don't correspond.  From roughly four thousand years ago to roughly the start of the Common Era, the spring equinox, starting point of the astrological sign of Aries, occurred against the background of the constellation Aries.  It was probably during that time that the signs were given the names by which we know them now.  For the last twenty-one hundred years or so, the equinox has been traversing the constellation of Pisces, and it's now passing through the rather imprecise boundary between Pisces and the constellation of Aquarius.  Were you around for [musical cue] "This is the dawning of the Age of Aquarius, Age of Aquarius, Aquarius, Aquarius"?

I'm not convinced that harmony and understanding, sympathy and trust abounding, are any more likely for the next couple of millennia than they were for the last.  But I'm certain that in about six thousand years, the Perseid meteor shower, which now graces the season of Lughnasadh, will instead provide an annual May Eve light show.

I wish I could be as certain that our descendants will still be around to wonder at it, to slip outdoors to the hillsides and rut under the shooting stars.