The longest total solar eclipse of the century—to be unsurpassed in duration until June 13, 2132—was witnessed today by millions as a swath of Asia was cast under the moon's shadow that cut through parts of India and China. I journeyed to north central India to try to catch a glimpse of one of nature's most awesome spectacles. I found the entire country excited by the eclipse. Many thousands traveled to the zone of totality, whereas in many places an age-old superstition still held sway.

PATNA, Bihar State, India—At 4 A.M. local time, when roads are typically deserted in and around this ancient city of two million on the banks of the Ganges river, traffic was already heavy. By sunrise at 5:10, expectant crowds were amassed at Gandhi Maidan (Patna's counterpart to New York City's Central Park) armed with solar goggles and telescopes. Fast-moving monsoon clouds were approaching overhead and covered the eastern horizon, but the hordes of watchers kept their fingers crossed. The mood was festive: a multicolored tent had been erected; music and announcements blared from loudspeakers. Even the police, called in to maintain law and order, seemed more interested in joining the fun—a far cry from the previous day, when a crowd that had lined up to buy solar goggles became violent after the stock of 15,000 ran out.

In Varanasi and Allahabad—equally old cities a few hundred kilometers upstream on the Ganges and among the holiest sites for India's 850 million Hindus—crowds started gathering in predawn hours for the ritual bath that observant and superstitious Hindus take during a solar eclipse. In Hindu mythology, the demon Rahu swallows the sun god Surya periodically in a short-lived triumph of evil over good, but Rahu has a hole in his stomach, so Surya manages to escape. In any case, many Hindus still regard a solar eclipse as particularly inauspicious and shutter their temples, abstain from eating, throw away their leftovers, and take a bath in the Ganges or other holy body of water.

This eclipse was no exception. By daybreak the number of bathers had swelled to a few hundred thousand. All along the river's route, from Haridwar to Varanasi and Allahabad and on to Patna and Kolkata, people came to take a dip and ward off evil. (By end of the eclipse, millions had taken a dip in the Ganges; in Varanasi, there was a stampede on the banks of the river that left one person dead.)

But probably nowhere was the crowd as large and expectant as in Taregna, a small, dusty village near Patna to which thousands and thousands of Indians had traveled. (News reports put the crowd between 60,000 and 100,000.) Taregna (the name derives from counting stars) is where Aryabhata the Elder, the sixth-century Indian astronomer who is often credited with the invention of zero, had undertaken his celestial observations. Roads leading to Taregna were clogged for hours.

In contrast to the superstitious taking ritual dips, scientists had gathered around the country to make eclipse observations. Certain measurements can only be made during solar eclipses. (Einstein's theory of general relativity was first observationally tested by astronomer Arthur Eddington during a 1919 solar eclipse.)

During today's eclipse, a few scientists led by Brajesh Kumar from the Udaipur Solar Observatory (USO) had gathered on a rooftop in Patna to study the sun's corona—its hard-to-see outer atmosphere. Another group from the USO had requisitioned an Indian Air Force transport plane to do solar spectroscopy. Others were studying the polarization of the light to get a better understanding of the sun's coronal magnetic field.

The solar eclipse started around 5:28 A.M. in Patna and surrounding areas. Thick rain clouds moved in and out as the eclipse progressed, so it was a matter of luck whether or not the critical minutes of totality were visible. In Patna and Taregna, totality was obscured, much to the disappointment of those amassed there. Yet a few kilometers away, on roads leading away from the city and in nearby towns such as Vaishali and Gaya, during the minutes when the moon's shadow covered the sun completely the rare sight was visible.

The eclipse started with the moon's shadow creeping across the face of the sun. The sun looked like a crescent moon through solar glasses or a filtered telescope. An hour later, just minutes before totality, the sky darkened considerably. The entire world looked different in color as bands spread across the sky. Then there was a final diamondlike ring around the sun before total darkness set in. Day had suddenly turned into night, and the temperature dropped. At this point, only a few prominences from the sun's corona were visible. To those watching, it felt wondrously eerie. Then, slowly the moon moved on, and a sliver of sun reemerged. After a few minutes, the solar disc swiftly revealed itself. By about 7:30 it was all over, and a brilliant sun shone with an intensity that promised another steamy day in Bihar.