Photo taken on July 11, 2009 shows the sketch maps illustrating the whole process of the full solar eclipse during a popular science exhibition on the introduction to the forthcoming 2009 Full Solar Eclipse at the Shanghai Science & Technology Museum in Shanghai, east China. The upcoming full solar eclipse, predicted to betide on July 22 and believed to be the longest of its kind in 500 years, will be visible in most parts of the Shanghai Municipality.

    Thundershowers or thick clouds may overcast many cities in the Yangtze River Valley, including Shanghai, Chongqing and Wuhan as well as the eight sites with the best views recommended by the National Astronomical Observatories, according to local weather stations.

    Jiaxing City, eastern China's Zhejiang Province, is one of the places where the eclipse can best be observed. All its hotels and inns are fully booked by eclipse watchers, 6,000 of whom traveled from abroad, according to local tourism administration.

Local citizens watch the sketch maps illustrating the whole process of the full solar eclipse, during a popular science exhibition on the introduction to the forthcoming 2009 Full Solar Eclipse at the Shanghai Science & Technology Museum, in Shanghai, east China, July 11, 2009. The upcoming full solar eclipse, predicted to betide on July 22 and believed to be the longest of its kind in 500 years, will be visible in most parts of the Shanghai Municipality.

    "We have never seen such a huge number of foreign tourists flocking in," said Zhou Hongxia, deputy director of the local tourism administration.

    Enthusiastic eclipse observers should prepare themselves for possible bad weather, said Su Yi, head of Tianjin Astronomical Society.

    "Of course, a sunny day will be optimal," he said, as observers can enjoy a panoramic view of the corona, Bailey's beads and the backdrop of a starry sky, he said.

    Rain or shine, the observer will still experience darkness and may even see the eclipse vaguely through the clouds, said Su.

    National Astronomical Observatories have placed a number of live studios within the totality path. In the worst case, people can watch the scene via live coverage on TV or on the Internet, as long as one studio can observe the scene.