(Space.com) On Tuesday, June 5, skywatchers in North America will have their last chance to see Venus pass in front of the sun for over a century. Because of the International Date Line, this event will occur on Wednesday June 6 in Asia, Australia, Africa, and Europe.
This event, called a transit of Venus, is one of the rarest sights in astronomy. Transits of Venus occur in pairs 8 years apart, each pair separated from the next by over a century. The last pair occurred in 1881 and 1889, and the next pair will occur in 2117 and 2125. This week’s transit is paired with a transit which occurred on June 8, 2004.
Why are transits of Venus so rare?
As the graphic associated with this guide shows, Venus’ orbit is tilted by 3.4 degrees as compared to the Earth’s orbit. As a result, most of the time Venus passes either above or below the sun when Venus is inferior conjunction with the sun (between the sun and Earth). Only when both Venus and Earth are at the points where the two orbits cross can we see Venus in front of the sun.
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