On June 5, skywatchers will have their last chance to glimpse a rare celestial spectacle, a “transit of Venus,” in which the planet passes directly between Earth and the sun. Venus will take six hours to march across the star’s face, appearing as an inky black dot in silhouette against the looming solar disk.
After that, the sun-shadowed Venusian outline will disappear until 2117. Because the planet’s orbit is slightly off-kilter, its solar transits come in pairs spaced eight years apart, with more than 100 years between pairs.
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