The Collins Observatory at Colby College will be open to the public for area residents interested in observing the transit of the planet Venus past the Sun on Tuesday, June 8. The transit begins at 1:15 a.m. while the sun is well below the horizon, and lasts until 7:25 a.m., when the silhouette of Venus leaves the Sun, according to Murray Campbell, the William A. Rogers Professor of Physics and Astronomy, who will conduct the observatory’s open house. Portable telescopes protected for safe viewing of the sun will be available at sunrise, 4:56 a.m. The main observatory cannot be used until 7:00 a.m. due to the tree line. Clear weather is needed to see the transit, and information on conditions will be available in a recorded message at 872-3251 prior to the event.

The last transit occurred in 1882, Campbell said. By observing from different geographic locations the length of time that Venus was in front of the Sun, 18th and 19th-century astronomers were able to determine the distance from the Earth to Venus and, using Kepler’s Third Law, from the Earth to the Sun. Perhaps the best known observer of a transit was Captain Cook in 1769, who was in Tahiti, but others observed that transit at locations including Hudson’s Bay, Canada, the tip of Baja California, Mexico, near Philadelphia. Pa., and in Greenwich, England.

An optical problem called the “black-drop effect” limits the accuracy of determining the distance to Venus using data from the transit. Modern astronomers use more accurate radar measurements for the distance to Venus, but observatories around the world will observe the transit optically.

No one should look directly at the Sun, Campbell stressed. Looking through unprotected binoculars or telescopes results in instant eye damage and can blind the observer. Colby’s Collins Observatory will provide views through safely protected telescopes.

Web sites with information about Venus’s solar transit include http://sunearth.gsfc.nasa.gov/sunearthday and http://www.transitofvenus.org/safety.htm.

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