IT'S unlikely many Mexicans will believe, as their Aztec ancestors did, that a jaguar is gnawing on the sun. But the fascination with the total eclipse, that will occur here on Thursday, is as intense as ever.El Eclipse will be one of the longest and best-witnessed total solar eclipses in history. The moon's shadow will trace a 130-mile-wide path on the Earth's surface from Hawaii, across the heart of Mexico, through Central America, and down into the jungles of Brazil. Assuming clear weather, about 50 million Mexicans should be able to see the rare day-becomes-night spectacle. It will be the last total solar eclipse visible in North America until the year 2017. And "ecliptophiles" will have to wait 141 years to see the moon park in front of sun for as long a period, say astronomers here. In the Mexican state of Baja California, where at least 300 scientists from around the world are gathering, the sun will be completely hidden for almost seven minutes. In addition to the opportunity to study the sun's corona (outer edge), this eclipse is occurring during a peak in solar flares and magnetic storms. "An unbeatable display of nature," said NASA scientist Steve Maran in a recent press conference via satellite from Washington, D.C. The entire process of "eating" the sun will last about three hours starting shortly after 10 a.m. in Baja California. On the Baja Peninsula, where it seldom rains, hotels and campgrounds are booked solid, with 50,000 to 100,000 tourists expected. And lodgings can only be obtained for a minimum of a week. There is, however, a controversy raging in Mexico over whether people should or should not watch the eclipse for fear of injuring their eyes. "The best is not to look directly at the sun at all. But if you're going to look, use an approved filter," says Pilar Conteras Irigoyen, a science spokeswoman for the Universidad Nacional Autonoma de Mexico (UNAM). As she gives this advice, she is hawking filters at 1,500 pesos (50 US cents) each to a crowd at the La Raza Metro station. A nearby UNAM display advises people to use a certified filter, to watch the sun's reflection in water, or to watch it on television. Sunglasses or exposed photographic film will not protect one's eyes, it says. Mexican health officials and several famous actresses in television commercials are encouraging people to view the eclipse indirectly via TV or some other means. Rodolfo Neri Vela, Mexico's first astronaut - along with many scientists - counters that it is safe to watch without any filter during the nearly seven minutes when the sun is completely obscured. The danger to eyesight exits only during the phases before and after the total eclipse, he says. In a recent newspaper article, he railed against creating an atmosphere of false alarm and "treating the public as if they were children." To avoid "chaos" on the interstate highways, about 1,600 Mexican federal police will require all cars to pull over for 15 minutes before and after the total eclipse. All airports in Mexico will be closed from 1 p.m. to 4 p.m. Folk festivals and ancient ceremonies are planned to coincide with the eclipse at various archeological sites around Mexico, where pre-Hispanic celestial observers pioneered precise astronomical predictions. Although simple curiosity and ardent entrepreneurship seem to have supplanted much of the superstition and ignorance surrounding the event, one Mexico City newsstand is doing a brisk business with a magazine entitled "How to get good luck from the eclipse." Presumably, the magazine advises one to become a vendor of eclipse paraphernalia before the cosmic shadow arrives.