Rare transit of Venus

It sounds like the title of a book by Henry Miller. And while it’s an astronomical event rather than a novel, it has still produced all of the triumph and tragedy, interest and excitement we expect from a good read.

It’s called the transit of Venus. And as the name suggests, it refers to Venus passing between the Earth and the sun, thereby allowing us to see Venus moving across the sun.

Since Venus is much farther away from us than the moon, it doesn’t produce a solar eclipse. Rather, Venus appears as a black dot, sort of like a moving beauty mark on the face of the sun.

Also unlike an eclipse, the transit of Venus is a very rare event. Although the last such transit was just eight years ago, in 2004, the next will not occur until 2117. Transits occur in pairs eight years apart, but after a pair of transits has been completed, we have to wait either 121.5 or 105.5 years for the first of another pair.

Despite the difference between transits and an eclipse, there are also similarities. Transits create a great deal of excitement among laypeople and astronomers alike, and offer unique research opportunities for the latter group. And it is these research opportunities, combined with the rarity of the transits, that have led to both triumph and tragedy.

Scientists realized early on the research value of the transits, and Jeremiah Horrocks was able to estimate, from his observations of the 1639 transit, both the size of Venus and the distance between the Earth and the sun.

Horrocks’s estimates, while far more accurate than any up until that time, were not perfect. Hence, famed astronomer Edmund Halley suggested that the 1761 and 1769 transits offered the opportunity to further refine estimates of the astronomical unit – the distance between the Earth and sun.

This required that astronomers journey to various parts of the world to view the transit. In 1760, one such astronomer, Guillaume Le Gentil, ventured from his homeland of France but due to war, didn’t make his intended destination of India. Gentil was therefore still on a ship during the transit of 1761, and could not make observations.

Nonetheless, he decided to wait eight long years for the next transit, and built a small observatory in India in 1768. And then, despite good weather all week, the sky became overcast on the day of the transit, once again making observation impossible.

If that weren’t enough, Gentil became ill with dysentery, and when he finally arrived home in 1771, he discovered that he had been declared dead, lost his position with the Royal Academy of Sciences, his wife had remarried and his relatives had plundered his property.

Nonetheless, Gentil did apparently remarry and recover his position. And the 1761 and 1769 transits did result in improved measurement of the astronomical unit.

Now that astronomers have moved well beyond our own solar system, the 2012 transit offers the opportunity to refine techniques for discovering “extrasolar” planets. And as always, it offers the rest of us a chance to witness a rare astronomical event, one that will be visible to us between 3 p. m. and 8 p. m.

Like an eclipse, the event should not be viewed without special equipment. And if you’re not familiar with such equipment, and you value your vision, it’s best to attend a facility like the Gordon MacMillan Southam Observatory at the H. R. MacMillan Space Centre, which will provide various means for safe viewing and will provide interpreters to discuss the event.

Of course, despite the advancements over the centuries, we are all still at mercy of the weather. And judging by the forecast, things don’t look promising right now. But in that event, the Space Centre will also have a feed from Hawaii. And in any event, things could be a lot worse:

Just remember Guillaume Le Gentil.