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Rare Sighting For Venus Watchers PDF Print E-mail
Written by Andres Chavez Sun Staff Reporter   
Thursday, 07 June 2012 03:36

E. C. KRUPP, GRIFFITH OBSERVATORY

If you missed the Transit of Venus on Tuesday, June 5, from 3:06 p.m. to 8:02 p.m., you're totally out luck because the next one won't happen for another 105 years!

The Transit of Venus occurs when the planet passes directly between the Earth and the Sun. When viewed through the proper lens, Venus appeared as a small black dot as it transversed the surface of the Sun.

Long considered a wonder to scientists and other observers, the Transit of Venus is among the rarest of predictable phenomena. The transits occur in a pattern that repeats every 243 years, meaning the next one won't be seen until 2117.

More than just a celestial show, the Transit of Venus was of scientific importance in the history of astronomy because it allowed the measurement of the solar system. Venus transits occur like clockwork, appearing in pairs eight years apart, either in June or December. On this schedule, a June pair will come 121 1/2 years after a December pair while the December pair follows a June pair after 105 1/2 years. As seen from Earth, only transits of Mercury and Venus are possible.

Transits of Venus and Mercury occur at slightly different times, as seen from different locations on the surface of the Earth. The diameter of our planet (7,926.41 miles at the equator) is known and when compared to the distance to Mercury and Venus, astronomers are able to triangulate on the planets from various points on Earth when they are seen against a bright background as the surface of the Sun.

This allows the difference between the distances of the planet and the Sun to be calculated. Due to its considerably larger size, Venus is better for this purpose than Mercury. In the 18th and 19th centuries, the Venus transits provided astronomers with the best opportunity for measuring the absolute scale of the solar system based on Kepler's third law.

Published by Kepler in 1619, the third law establishes the relationship between the distance of planets from the Sun, and their orbital periods. The third law was also known as the harmonic law. Kepler viewed the workings of the solar system as the "music of the spheres" which followed precise laws, and could be expressed it in musical notation.

Currently, Kepler's third law is used to estimate the distance from an exoplanet (planets found in solar systems outside ours) to its central star, and helps to determine if this distance is inside the habitable zone of that star.

Modern techniques have rendered the Transit of Venus as merely a chance to view a rare and striking event. Tracking of interplanetary spacecraft, and especially radar ranging to the inner planets, finally achieved the precision sought by astronomers for centuries.

The next Transit of Venus will happen on Dec. 11, 2117. The last Transit of Venus occurred on June 8, 2004, but was not visible in Los Angeles. The last time it was visible from Los Angeles was Dec. 6, 1882.

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Last Updated on Thursday, 07 June 2012 21:03