Reverent as pilgrims, my two children and I are journeying to a faraway place where dawn breaks and dusk falls twice on the same day, and where the stars come out with the sun still overhead.

Our destination lies in the southern expanse of the Black Sea near Turkey, under the shadow of the moon. There, at an exotic convergence of latitude and longitude, at predicted but ephemeral coordinates in space and time, we will witness the miracle of a total eclipse of the sun.

The eclipse promises all the spectacle of a coronation or a command performance. But a sudden squall--even a passing blanket of clouds--could obscure it from view, despite all our dreams and difficulties in coming to this place.

Attraction turns to obsession for some eclipse-chasers, who stand ever-ready to travel any distance for yet another occult fix. I once met a nonagenarian who had followed 14 solar eclipses. He bore the telltale crescent-shaped scars on his retinas, like hidden battle ribbons won for solar valor. In his youth, someone must have forgotten to cover this man's eyes at the dangerous moments (leading up to and immediately following totality) the way my mother shielded mine with layers of black-and-white film negatives that long-ago morning in the early '50s when she took me to see a partial eclipse on our way to school.

Each eclipse comes as a shock, no matter that it occurs on schedule, according to predictions forecast centuries in advance. No two look quite the same, and every one, by its nature, overturns the world order. Even the most experienced observers simply gawk at the sight, sensing the same bizarre disorientation that birds and animals must share, as they hasten to their nests or burrows through the sudden midday darkness that an eclipse spreads in its wake.

Only the Earth and the moon--and no other planets or satellites in the solar system--can figure in the ceremony of totality. By a stunning accident of cosmic gravity and geometry, these two bodies alone possess the precise size and distance relationships to periodically extinguish the central fire of the sun. The puny moon, only one four-hundredth the sun's diameter, lies 400 times closer to the Earth. Thus the moon exactly matches the sun in apparent size in our skies, as though they were two halves of the same grapefruit. When the new moon dogs the sun across the daytime sky, it can sometimes step in front of that bigger, brighter heavenly body and obliterate it from our view. To some believers, this coincidence serves as proof of the existence of God.

Although the moon turns new once a month, it obscures the sun approximately just once in two years. Unlike the long winter or the long-awaited spring, the eclipse season lasts only a few moments. And instead of arriving in a whole hemisphere, it touches down upon a single narrow swath of land and water--often so remote as to be almost inaccessible. (The path of this coming eclipse cuts clear across Europe and parts of Asia, through unusually populated areas.) The eclipse brings a weather change that lowers temperatures by 10 or 15 degrees at a stroke. But the abrupt cold spell, like the eclipse itself, passes hurriedly through the region like a shiver down the spine.

No total eclipse can last much longer than seven minutes, because of the Earth's persistent turning at 1,000 miles an hour and the moon's unwavering progress around her. Yet I once knew a man who had raced the moon across the sky in a high-flying private jet, and stretched out totality to an unnatural eight and one-half minutes.

My children and I will behold Wednesday's eclipse from the deck of a ship temporarily adrift near the Bosporus. Together with 300 other people, we shall be united on this vessel, the Stella Oceanis, in this single purpose. As a veteran of the 1991 eclipse, which I watched in the Sea of Corts at the tip of Baja California, I already know what will happen.

At "first contact," the eastern rim of the moon just grazes the western rim of the sun. Then gradually, inexorably, the moon encroaches on the sun's disk, and dimples it, as though taking a bite out of a cookie. Over the course of an hour the darkened part will grow steadily larger, and the crescent sun shrink to nothing behind the moon.

"Bailey's beads," someone will whisper, naming the string of bright baubles visible when only a narrow arc of sunlight shines through the chain of mountains on the moon.

"Diamond ring." The last flash of sunshine sparkles atop the remaining sliver of light before the moon completely swallows the sun.


This will be the time to remove our protective glasses and gaze naked-eyed at the two bodies superimposed on one another. After the foreplay of partiality, teased out over 90 minutes, this union is explosive in its impact. The temperature plummets. The sky switches, as if by command, from the hot glare of a summer noon to a crepuscular blue. The blackness of the moon is a pool of soot, flat as flannel or felt. And all around that black pupil streams the sun's glorious corona, ordinarily invisible, but now an enormous, spreading presence, glowing like burnished platinum, reaching out to touch stars that have been absent from the night sky for months.

The same moon that shutters the sun's light will silence the passengers and crew members gaping skyward. No one will say a word. Flaming red whorls of solar prominences will spurt from the moon's black disk--each of these a huge hump of pure hydrogen gas, towering 50,000 or 80,000 miles above the sun's surface, and clearly visible to the unaided eye during totality. The duration of an eclipse could be 6 minutes, 53 seconds, like the "Eclipse of the Century" on July 11, 1991, or the predicted 2 minutes, 23 seconds for this final total solar eclipse of the millennium. Either way, it feels by turns like an instant, like an eternity. For a few fearful moments of eerie twilight, one cannot help but wonder whether the world will stay like this forever.

Then the moon will begin to reveal the sun again, and the spell will be broken. Voices will return. People will sit up, look around, through their tears, at the other tear-stained faces.

Moments later, our temporary Mecca will vanish like a breaking wave, for nothing distinguishes this site save the brief drama to unfold above it. The black magic sun will desert the indifferent waters, promising to reappear elsewhere, months and years hence.

I had hoped to take my two teenagers to see the last total solar eclipse, in February 1998, near Aruba. I chortled then at the unusual good fortune of finding the eclipse path lying along a tropical paradise in mid-winter--as opposed to Siberia in early March, say, as happened in 1997, or the Sahara in the summer of 1973. But my daughter got a part in the high school play, and the performance date conflicted with the eclipse.

Other excuses--summer jobs, preparations to leave for college--could have scotched this trip just as easily, except that I insisted this time. I wasn't going to let the event slip by again. As we approach the midline of totality's path, solemnly I shall give my children the same advice a wise, experienced astronomer shared with me on the correct technique for viewing an eclipse: "Look up, look up, look up!"

Some people anticipate a total solar eclipse as a once-in-a-lifetime experience. You're not quite complete until you see one, they reason, but after you do, you move on to other things. The pyramids. The Inside Passage. The Great Wall of China. But the truth, for some of us at least, is that the first eclipse merely whets the appetite for the next.

Dava Sobel is the author of "Longitude" and "Galileo's Daughter: A Historical Memoir of Science, Faith, and Love," which will be published by Walker this fall.