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In June 2012, Venus will pass across the face of the Sun for only the second time this century and the last time until December 11,2117 (105 years!). When Venus lines up between the Earth and the Sun, its as close as it ever comes. It will apear over 58 arc-seconds wide (a little less than 1/30 the width of the Moon or Sun in the sky).
2004 Venus transit, courtesy of National Solar Observatory/AURA/NSF
Johannas Kepler predicted the first Venus transit in 1627 would occur in 1631. Unfortunately, the 1631 event occurred below the horizon in Europe and went unnoticed. By the 1700's, Edmond Halley (of Halley's Comet fame) laid out the techniques and observations needed to measure the distance to the Sun using a transit of Venus. Kepler's laws of planetary motion explained the relationship of the various orbits, not a true measure. If the Earth-Sun distance could be accurately measured, then the true size of the solar system could be understood. Expeditions were mounted in the late 1700's by various teams, including Charles Mason and Jeremiah Dixon (also known for the Mason-Dixon line!). The results were marginal due to the "black-drop effect" as silhouette of Venus neared the limb of the Sun. The transits of 1874 and 1882 did little to improve the measurement. The Earth's atmosphere and telescope imperfections made the "seeing" fuzzy at the critical contact points. At the start of the 20th century astronomers used the near-Earth asteriod Eros 433 to determine the astronomical unit. Today, radio signals from spacecraft orbiting distant planets have refined the measurement.
While Venus passes in front of the Earth about every 584 days, the orbit of Venus is inclined ( by about 3.4 degrees) relative to the Earth. Most of the time Venus passes above or below the Sun as viewed from Earth during this conjunctions.
While a transit of Venus no longer holds a scientific value, it is a rare and stunning event. Oliver Lee State Park and the Amateur Astronomers Group will have specially-filtered telescopes and glasses (limited) available for the public to view this "once in a lifetime event". Venus will look like a black dot silhouetted against the Sun's brilliant disk. The entire transit event will not be viewable from Oliver Lee state Park due to the rotation of the Earth, however we will witness the initial transit and approximately half of the transverse across the face of the Sun (weather permitting, of course!).
The AAG will post images from the transit on this page...... STAY TUNED !!
