July 1991 (Mexico) Expedition Final

General. 300 people convened in Puerto Vallarta, Mexico as a base of operations for observing the July 11, 1991 total eclipse of the sun. The expedition was unique in that its goal was to position itself to see the most spectacular overall view of the eclipse, available near the southern edge of the path of totality. The expedition participants were not disappointed.

Preliminaries. The first 200 participants arrived in Puerto Vallarta on July 6, where they were met at the airport and transported to the beautiful Buganvilias Sheraton Resort on the beach. At the special check-in desk, expeditioners picked up their eclipse materials and identification badges, and were offered the opportunity to sign up for inexpensive side trips to take away lasting memories of the area. (The side trips included a cruise on the Princess Vallarta with snorkeling, a shopping tour of the city, a plantation and beach tour with swimming, and a horseback riding trip.) The materials provided included mylar solar filters for viewing the partial eclipse, the US Naval Observatory circular for this eclipse, the Astronomical Calendar for 1991, sky diagrams at eclipse time, and photography information.

Activities began with a courtesy cocktail party and get-acquainted reception. This was followed by a discussion of plans for observing the occultation of the Pleiades star cluster by the crescent moon, conducted by expedition astronomer David Dunham. Although the Pleiades event itself was clouded out at Puerto Vallarta, it was reconstructed by computer simulation using "Dance of the Planets" for the entertainment of the participants.

The astronomy week program also included three lectures by astronomer Tom Van Flandern: one on new ideas in cosmology; a slide tour of the solar system; and new solar system models, such as the latest about prospects for finding a "Planet X" beyond Pluto. There were also two sessions specific to eclipse preparations. One dealt with photography and video recording, and general viewing safety considerations. The second dealt with the logistics of travel to the primary viewing site or possible alternatives, and arrangements at the site.

Two days before the eclipse the last 100 participants arrived, in time for all the eclipse preparations but with little time to visit in the area. About half of the participants brought along telescopes and/or recording equipment.

Weather. Puerto Vallarta itself is slightly outside of the total eclipse path. It is located on the west coast of mainland Mexico, about midway between Mazatlan and Acapulco. Puerto Vallarta is surrounded by coastal mountains on three sides and the ocean on the fourth. Clouds tend to form at the mountains as weather patterns advancing from west to east are forced to higher altitudes; and in July (the rainy season) it is rather cloudy inland from there. However on the windward side away from the mountains, clear skies are common, and eclipse-viewing conditions were promising. The first landfall of the southern limit of the eclipse track occurred just north of Puerto Vallarta (the southern limit missed both Hawaii and Baja California); and no other site further down the eclipse track expected weather conditions any better.

We chose a site at the optimal 4 kilometers inside of the predicted southern limit, right at the ocean and several kilometers from the mountains. At this location we found the rural Mexican village of Sayulita, with about 3000 residents. The villagers welcomed our expedition, and allowed us to set up and use the facilities in their spacious schoolyard, where we had access to electricity and shelter. Most of the villagers, however, chose to heed the warnings of the Mexican government, and stay indoors during the eclipse, despite our encouragements.

The morning in Sayulita dawned clear, and all nine buses carrying participants disembarked there, although they were prepared to go further into the eclipse path if the weather threatened. All morning, clouds continued to form over the nearby mountains to our east, but the western sky remained quite clear. By an hour before totality, with the partial eclipse well underway, the clouds extended themselves across our zenith. (Totality would occur with the sun less than two degrees from the zenith.) Although they were thin enough to see the sun through, the clouds caused considerable worry. But with temperatures already falling noticeably, the clouds near the sun dissolved about 20 minutes before totality, and remained away until long afterwards. This "eclipse effect" on the clouds occurred just as expected at our site. (On the other side of the mountains, it would cause clouds to form). Nonetheless the clouds heightened anxieties until the eclipse cooling did its work.

Observations. The eerie light of an approaching eclipse was readily apparent to all. Even by 30 minutes before totality, crescent images of the partial eclipse could be seen on the ground. At 10 minutes to go, many people spotted Venus; and not long afterwards, Jupiter. Projected images of the sun's disk showed many sunspots, and one especially large sunspot group. Excitement mounted as the landscape grew darker, and stars became visible. A distant rooster crowed, and birds took their roosts. At three minutes to go, the first round of shadow bands appeared. They were lower in contrast than average, but had the usual effect of exciting and delighting the viewers.

Then came the three minute period of high activity. From sites near the path edges, the eclipse occurs in slow motion, with edge effects greatly enhanced. The thinning crescent began to break up into Baily's Beads for about 45 seconds before and after totality. However these were less conspicuous to the naked eye than in other eclipses, because the diameter of the moon was so much greater than that of the sun. But by 30 seconds before totality, a complete and startlingly beautiful diamond ring began to form as the corona (the sun's atmosphere) became visible along with the last brilliant bead of sunlight. This slowly faded out to reveal the totally-eclipsed sun in all its glory.

Observers were awestruck. The usually symmetric corona showed long streamers extending out on either side, a reminder of the recent intense solar activity. Correspondingly, major solar prominences (eruptions in progress) were seen by telescope along the Sun's limb beneath the coronal streamers. Perhaps most beautiful of all, the reddish-pink chromosphere remained visible at one limb of the sun throughout the 103 seconds of pure totality at our site, adding color to the phenomenon. Near the centerline, the red chromosphere (the inner corona) is visible for only a moment, giving rise to the expression "flash spectrum" for those who try to record it.

Reactions. Totality was followed by another 45-second period of edge phenomena in reverse order from the onset. When the last shadow bands had vanished and the observers caught their collective breaths, spontaneous applause broke out in the schoolyard. Comments of "fantastic" and "incredible" were heard from everywhere. One couple agreed that it was the most beautiful thing they had ever seen in their lives. A photography enthusiast said he just stopped everything during totality and watched the rest of the beautiful spectacle, mesmerized. One of the veteran professional astronomers was so distracted by the unprecedented beauty of the corona and chromosphere that he forgot to time the third contact. Another veteran of five eclipses with a unique perspective said that he was glad it didn't last longer because he couldn't have stood the sustained excitement another minute. Perhaps the most graphic comment by a first-timer: "I gave up trying to photograph it; I was too busy having an orgasm!"

Expeditioners gathered together again that evening for the closing banquet. But several participants with video records were able to show their captured treasurers, allowing everyone to relive the experience, and to see some views from different perspectives they had missed earlier. Some of the exposures were just right to bring out coronal detail, some just right for chromosphere colors, some brought out the Diamond Ring effect. David Dunham's video showed details of Baily's Bead formation, and movement patterns unique at the southern edge.

Cheers and applause greeted each new perspective as the video records were shown. It was agreed that these and the best stills would be woven into a video tape record of the entire expedition for later distribution to all participants. Emotions ran so high that the group could barely be brought back down long enough to hear reports from other sites in our on-line conference. Although saddened to hear that not all the other expeditions could share in our joy because of clouds at their sites, it seemed that nothing could dampen the enthusiasm of the evening.

As the expedition adjourned, there was one nearly unanimous sentiment exchanged: "See you at Eclipse Edge '94 in Rio!"