The experience of a lifetime:
Without a doubt, this month’s Venus transit was the experience of a lifetime. That’s because the next time the phenomenon occurs will be in 2117.
As the sun set on June 5, Venus made a rare and spectacular appearance and more than 700 people saw it from the Buehler Planetarium and Observatory. Venus actually passes between the Earth and the Sun every 583.9 days, but it rarely crosses directly in front of the Sun as it did this month.
A historical wonder
A Venus transit is of great historical significance to astronomers. A Venus transit was first predicted and observed in 1639. For many years, only relative distances were known about our solar system, but it was understood that accurate time and position measurements of a Venus transit could lead to actual distances of the space between the planets and the Sun. Edmund Halley formulated a detailed plan for how the transits of 1761 and 19769 should be observed, long after his death, in order to measure the distance of the Sun to the Earth. After the 1769 transit, the distances were known to within 5 percent of modern-day values.