<P> There is a long history of observations of gravity - related phenomena during solar eclipses, especially during the period of totality . In 1954, and again in 1959, Maurice Allais reported observations of strange and unexplained movement during solar eclipses . The reality of this phenomenon, named the Allais effect, has remained controversial . Similarly, in 1970, Saxl and Allen observed the sudden change in motion of a torsion pendulum; this phenomenon is called the Saxl effect . </P> <P> A recent published observation during the 1997 solar eclipse by Wang et al. suggested a possible gravitational shielding effect, which generated debate . Later in 2002, Yang and Wang published detailed data analysis, which suggested that the phenomenon still remains unexplained . </P> <P> In principle, the simultaneous occurrence of a Solar eclipse and a transit of a planet is possible . But these events are extremely rare because of their short durations . The next anticipated simultaneous occurrence of a Solar eclipse and a transit of Mercury will be on July 5, 6757, and a Solar eclipse and a transit of Venus is expected on April 5, 15232 . </P> <P> More common, but still infrequent, is a conjunction of a planet (especially, but not only, Mercury or Venus) at the time of a total solar eclipse, in which event the planet will be visible very near the eclipsed Sun, when without the eclipse it would have been lost in the Sun's glare . At one time, some scientists hypothesized that there may be a planet (often given the name Vulcan) even closer to the Sun than Mercury; the only way to confirm its existence would have been to observe it in transit or during a total solar eclipse . No such planet was ever found, and general relativity has since explained the observations that led astronomers to suggest that Vulcan might exist . </P>

How many years does it take for the moon to cover the sun