Transit of Venus

Written by on December 2, 2009 in Learning with 0 Comments


The story of the transit of Venus is one that outlines some of the most significant scientific discoveries ever made, discoveries that would profoundly change the way we see ourselves and our place in the universe.

A transit of Venus occurs when Venus comes between the Earth and Sun and partially eclipses the solar disk. They are some of the rarest and predictable astronomical phenomena, always happening in pairs separated by eight years. Each pair follows another in repeating intervals of 121.5 and 105.5 years. Our last transit was in 2004, the next will happen on June 6th, 2012.

Mankind has only been witness to six events since the invention of the telescope in 1609. The first one was observed by Jeremiah Horrocks and William Crabtree on December 4, 1639. As the silhouette moved across the Sun certain key measurements had been made and from this the first determination of Earth’s distance from the Sun was calculated. This was all made possible using Johannes Kepler’s three laws of planetary motion and Edmund Halley’s concept of ‘parallax’ measurement.

Parallax measurement uses trigonometry to calculate the displacement of an object from two different stations or points of view on the surface of the earth. Calculations of the angles involved yield accurate distances, hence the separation between the Earth and Sun was discovered. From there the rest of the planets were easily measured and within a short period of time we had an accurate scale of the solar system.

This scale then allowed us to deduce a vast range of other parameters – ie. size, mass, atmospheric composition, surfaces, internal structures, magnetic and electric fields and elementary particles. Then, beyond the physical characteristics, we even began to postulate how the planets may have formed and how the solar system would eventually end.

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