Venus Transit Viewing at College Observatory

Categories: For Faculty, For Staff, Uncategorized

On Tuesday, June 5, local residents will have what will be literally the only opportunity in their lifetime to view a rare astronomical event–a transit of Venus. Shortly before sunset, Venus will pass directly between Earth and the Sun. Transits of Venus occur in pairs eight years apart, separated by more than a century. The last transit was on June 8, 2004, but the next one will not occur until December 11, 2117.

The Physics Department at Middlebury College plans to have several rooftop telescopes available to view the transit. All are equipped with filters that permit safe viewing of the Sun. The telescopes on the roof of McCardell Bicentennial Hall will be open from 5:30 p.m. until the Sun sets at about 8:30, providing the weather cooperates.

One should NEVER try to view the Sun with a telescope, binoculars, or even with the naked eye without a filter specially designed to block almost all of the Sun’s light.  Looking for even an instant can cause severe and permanent eye injury!

Venus should start to pass in front of the Sun at 6:04 p.m., and its silhouette will gradually move across the Sun’s face. It will complete only about a third of its passage before the Sun sets in Vermont at 8:40 p.m.

If the weather is clear, the rooftop telescopes and the 24-inch telescope in the observatory dome will reopen toward the end of twilight, at 9:15 p.m. They will remain open until 10:30 p.m. for viewing the stars and the nearly full Moon.

Transits of Venus have an interesting astronomical history. In 1716, Edmund Halley (of Halley’s Comet fame) realized that carefully timing a transit of Venus from different locations around the world could enable astronomers to calculate the distance between Earth, Venus, and the Sun, and hence the scale of the entire solar system, none of which were accurately known at the time. Halley knew he would not live to participate in this experiment; the next transit was in 1761.

For the transits of 1761 and 1769, a host of countries mounted expeditions to far-flung corners of the globe to time the event–the first example of a major international scientific collaboration. Despite immense effort and several successful observations, timings (and hence the distance measurement) were not as accurate as hoped because of a “black drop” effect that makes Venus’s disk stretch and blur into the edge of the Sun at the start and end of transits.

The best known voyage was that of Captain James Cook, who sailed for eight months across the unknown South Pacific to reach Tahiti to view the 1769 transit. (This is approximately the same length of time a journey to Mars would take today!) His expedition viewed the transit from what they named Point Venus. From there, Cook continued westward and became the first European to accurately map much of the Australian coast.

This event is free and open to the public, but will take place only if the sky is clear enough to get at least glimpses of the Sun. If the weather appears uncertain, visitors may call the observatory at 443-2266, after 4 p.m. on the afternoon of June 5 for a status report.

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