This June 8, 2004 photo shows the transit of Venus, which occurs when the planet Venus passes between the Earth and the sun, pictured in Hong Kong. (AP Photo/Vincent Yu,File)
This June 8, 2004 photo shows the transit of Venus, which occurs when the planet Venus passes between the Earth and the sun, pictured in Hong Kong. (AP Photo/Vincent Yu,File)

On Tuesday,  June 5, people in most parts of the world have a good chance of witnessing a once-in-a-lifetime astronomical event called the transit of Venus.

It’s a planetary alignment which occurs when the planet Venus passes directly between the Earth and sun.

For those of us here on Earth, it’ll look like a little black dot beginning on the edge of the sun and gliding across the face of it over a couple of hours.

The transit of Venus is expected to occur at around 2209 UTC.  Of course,  clouds could obscure the view and people in Portugal, southern Spain, western Africa, and the portions of South America are unlikely to see the occurrence because that part of the world will be in total darkness the entire time of the transit.

The striking event occurs about once a century, in pairs, with around eight years separating each twin event.  This upcoming occurrence is the second in a recent pair of events, the first of which took place in 2004.

Tomorrow’s transit will mark only the seventh time the phenomenon has been seen since it was first observed in 1639 by Jeremiah Horrocks and William Crabtree of England.

In 1627, astronomer Johannes Kepler became the first person to successfully forecast a transit of Venus when he predicted the 1631 event.

According to NASA, the 18th century astronomer, Edmund Halley – of Halley’s Comet fame – came up with a way of using the transit of Venus to determine the distance between Earth and the sun. He suggested  measuring the start and end times of the transit from different points on Earth, using methods of triangulation to make the calculation.

If you want to watch the transit of Venus be sure to take precautionary measures. These people, for example are using solar viewing glasses to safely view the Sun. (Photo: NASA)

The method was first tried in 1761, but the international team’s efforts were unsuccessful due to poor weather and other factors.

Another effort, in 1769,  with observation points all over the world, proved more successful, providing statistical data that led scientists to calculate the mean distance from the Earth to the sun was around 150,838,824 kilometers. Using more modern, technologically-advanced equipment, scientists now say the mean distance from the Earth to sun is 149,600,000 kilometers. Seems that, with Sir Edmund Halley’s help, the 18th century calculations were pretty darn close.

Speaking of NASA, the space agency announced that Don Pettit, a flight engineer on the International Space Station, will photograph the event. It’s the first time the transit of Venus has been observed from space.  The astronauts aboard the ISS in 2004 weren’t able to see the transit because they didn’t have any solar filters which would allow them to safely observe it.

World map show visibility of transit of Venus on June 5-6, 2012. (Map: Michael Zeiler)

Observatories and other various science-oriented institutions from around the world will be opening their doors to host transit watching parties and events.

If you’re planning on watching the transit of Venus, please make sure to take precautions, since looking at the sun directly can cause serious damage to your eyes.  Experts recommend you use protective glasses or telescope lenses with special solar filters, or better yet, watch it on TV or the Web.  Good luck with your observations because the next set of transits won’t take place until 105 years from now, in 2117.




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