Eclipse Viewing on the Water

Ships and boats offer an opportunity for considerable mobility when seeking those few minutes of sunshine during the critical moments of an eclipse and can often overcome the limitations of a climatologically challenged land-based site. Figure 21, a graph of mean cloudiness along the track, shows that sites off both continents are cloudier than on the land. Mean cloud cover in the Indian Ocean off Africa rises slowly, but that in the Great Australian Bight is much greater than inland Australia. While ships off either coast would offer the benefits of mobility, a water-based location in the Bight can also bring the advantages that come with a much higher solar altitude.

The Great Australian Bight is a cloudy place in December, though the closer one moves toward landfall on the eclipse track, the better the weather prospects become (Figure 21). Unfortunately the trade-off is steep, with the sun declining rapidly in the sky as better weather prospects are approached. On the centerline south of Perth the solar elevation will be about 24 degrees while offshore from Ceduna, the sun will set before fourth contact. The best location along the track can only be determined on eclipse day according to the weather at hand, and so ship-board expeditions should position themselves on the center line in the middle of the Bight in order to be prepared to move either east or west in search of a break in the clouds. Considerable movement may be necessary in order to find such a break, for frontal systems typically stretch across several hundred kilometers and may require many hours of sailing to break free of cloud. A serious attempt cannot be made without access to satellite imagery and a detailed forecast.

Examination of satellite imagery for 1999 and 2000 suggests that the shipboard chances for a view of the sun on the Australian Bight are slightly lower or equal to that at an inland site in Australia. Wave heights off Africa average 1.5 to 2 meters and 2 to 2.5 meters off Australia. The values in waters near Africa are similar to those in the Caribbean in 1998. Wave heights are more variable in the Great Australian Bight, reflecting the more stormy nature of weather systems in the region.

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