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Catherine Pilachowski
IU Department of Astronomy
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Last modified: Wednesday, June 2, 2004

Public viewing of transit of Venus to be offered on June 8

Telescopes with solar filters available

BLOOMINGTON, Ind. -- On June 8, the planet Venus will slowly move across the face of the sun, appearing as a small black dot that might be mistaken for a sunspot. The rare celestial event, called a transit of Venus, last happened in 1882, when it created such excitement that spectators jammed Wall Street to see it.

The Indiana University Department of Astronomy and the Stonebelt Stargazers will host a free public viewing of the transit of Venus from 5:15 a.m. to 6 a.m. on the roof of the university's parking garage in the 900 block of East Atwater Avenue. Telescopes with solar filters will be set up so that visitors can view the transit safely. The garage will be open beginning at 5 a.m., and parking in the garage will be free until 7 a.m.

The transit lasts six hours, but it will be in its last hour when the sun rises in Bloomington on June 8. The sun will be barely above the treetops during the viewing from the roof of the parking garage.

During the 1882 transit of Venus, some astronomers risked their lives during voyages to remote locations in the Southern Hemisphere because they hoped to use careful observations of the transit to measure the distance between the Earth and the sun. That distance provided what was then the fundamental means to map the positions of heavenly bodies and determine the size of the universe. The measurement was so crucial to those tasks that the British Astronomer Royal in the mid-19th century called it "the noblest problem in astronomy."

Nations spent the equivalent of millions of dollars mounting expeditions to view and measure the 1882 transit of Venus from different locations on Earth. Those efforts resembled in their time the later Apollo missions to the moon and the robotic rovers now driving across the surface of Mars.

"In the 19th century it was really analogous to the space race," said Steven J. Dick, chief historian at NASA. "Any country that had a scientific reputation sent out transit expeditions. It was a race to see who could come up with the best technique and final answer."

Tales of some transit expeditions provide glimpses of key moments in history when astronomy intersected with wars, empires and exploration.

Great Britain, for example, sent Captain James Cook off to the South Pacific to observe a transit in 1769. His mission eventually took on far more importance as a means of expanding the British Empire. The Royal Society of London sent Charles Mason and Jeremiah Dixon to Sumatra to witness the 1761 event. Though they stopped in South Africa instead and measured the transit from there, they so impressed their superiors that they later were assigned to survey the border between Maryland and Pennsylvania, a project that resulted in the Mason-Dixon line.

The astronomer Johannes Kepler in 1627 was the first to realize that observers at different places on Earth could use the transit of Venus to calculate the distance to the sun. An observer in London, say, would see Venus from a different angle than would somebody in Cape Town, South Africa. Knowing the distance between the two cities, astronomers could use the angle between the observers to calculate the distance to Venus, and from that, the distance between Earth and the sun.

When Venus appears in front of the sun on June 8, astronomers will use the event for other purposes. Some will collect data on the atmosphere of Venus, while others will refine their techniques for studying planets around other stars. By watching how the sun's light changes when Venus transits, scientists can learn how to study transits of planets passing in front of their own parent stars.

The following are links to Web sites with information about the transit of Venus.

This NASA map shows where the transit on June 8 will be visible: http://sunearth.gsfc.nasa.gov/eclipse/transit/TV2004/TV2004-Map1b.GIF

The European Southern Observatory will provide a Webcast of the transit: http://www.vt-2004.org

The Exploratorium in San Francisco offers a Webcast of the event and instructions on observing the transit safely: http://www.exploratorium.edu/webcasts/index.html

The Smithsonian Institution has an online exhibit, "Chasing Venus: Observing the Transits of Venus, 1631-2004": http://www.sil.si.edu/exhibitions/chasing-venus/intro.htm