Al Ain scientist says Venus transit will be 'special'

Venus will transit across the Sun on Wednesday, a rare event that will not be repeated until 2117.

Dr Ilias Fernini and colleagues at UAEU. Courtesy of Dr Fernini

Dr Ilias Fernini, assistant professor of astronomy at the United Arab Emirates University in Al Ain (UAEU), will look up wistfully at the night sky in the early hours of Wednesday morning. If he could have his own way, the dawn chorus would start at 2.07am, allowing him to observe the transit of Venus in its entirety, as this faraway planet passes between the Sun and the Earth.

Instead, Dr Fernini will start his astronomical observations at 5.36am, and will continue his watch for the next three hours as Venus moves serenely across the face of the sun, dwarfed and silhouetted by the immensity of our nearest star.

"The transit is special," he says, "because we are observing an event that will not happen again in our lifetimes."

Such transits occur in a pattern that only repeats itself every 243 years. They happen in pairs, eight years apart, separated by gaps of 121.5 years and 105.5 years.

The last transit was in June 2004, only the sixth to have occurred since the first recorded observation in 1639, and the next will not be until 2117.

Despite their rarity, transits are now well-understood events that can be viewed in comfort and safety, as long as observers take adequate precautions when looking at the Sun. Dr Fernini's telescopes will be fitted with powerful filters to allow direct observation of the Sun and plotters that will project an image of the transit harmlessly onto the ground. For previous generations of astronomers however, this wasn't always the case.

In 1716, the British astronomer Edmond Halley called on the world's scientific community to unite in a global experiment to measure the transit that was predicted for June 6, 1761. According to Halley, if enough astronomers were stationed around the globe and enough data was collated, it should be possible to accurately gauge the size of the solar system.

Hundreds of astronomers rose to the challenge, braving the elements, war, pestilence and the unknown to make accurate observations of the event.

It is their remarkable story that historian Andrea Wulf recounts in her latest book, Chasing Venus: The Race to Measure the Heavens. Wulf is unstinting in her praise of the audacity, bravery and dedication to the pursuit of knowledge of all of those astronomers involved in the project. She describes the logistics of the Venus missions as mind-boggling.

"Imagine a time when there wasn't even a standard unit of measurement on Earth," she tells me. "When it took three months for a letter to get from Philadelphia to London. These men travelled to the furthest reaches of the globe simply because they thought this project was [that] important." The attempts to map the transits of 1761 and 1769 saw expeditions launched by both governments and the leading scientific societies of the day.

The British dispatched Captain James Cook to Tahiti and Charles Mason and Jeremiah Dixon to Sumatra. France sent astronomers to India, California and Siberia, while Catherine the Great sponsored eight expeditions to the icy wastes of the Russian empire.

Inevitably, some had more noble motives than others.

While the astronomers may have seen themselves as part of some international brotherhood of science, the British East India Company was more interested in the strategic and commercial advantages that an understanding of the size of the solar system would bring, particularly in the field of navigation.

Venus had exercised the imaginations of priests, artists and thinkers throughout history, but it was during the 17th and 18th centuries that the planet played a fundamental role in defining our current understanding of the universe and our place within it.

In 1610, Galileo's telescopic observations of the phases of Venus finally overturned the older geocentric theories of the solar system that had existed since before Aristotle. He proved that the planets orbited the Sun not the Earth.

In the 17th century, astronomers had understood the relative distances between the Earth, Sun and other planets but what they didn't understand was how far apart the planets were. As Wulf writes: "Eighteenth-century astronomers had a map of the solar system, but no idea of its true size. Without knowing how far the Earth really was from the Sun, such a map was all but useless. Venus ... was the key to unlocking this secret. As the brightest star in the sky, she also became the perfect metaphor for the light of reason that would illuminate this new world and extinguish the last vestiges of the Dark Ages."

It took a long while for the data from each transit to be collated and the results from the 1761 observations were riddled with irreconcilable mistakes. The stats from the 1769 transit proved more reliable, however, and allowed astronomers to determine the distance between the Earth and the Sun within a range of 92,900,000 to 96,900,000 miles - a figure very close to today's accepted value of 92,960,000 miles (149,604,618 kilometres).

In essence, the 18th-century efforts to observe the transits of Venus were the pre-eminent scientific endeavours of their time - equivalent to modern efforts to split the atom or send a man to the Moon.

For Wulf they occupy "a pivotal moment" in an era in which man tried to understand nature through the application of reason and, just like Diderot's Encyclopédie, Samuel Johnson's dictionary and Linnaeus's sexual classification of plants, they are the product of a very particular historical moment.

"The period of the 18th-century transits is a wonderful moment when two things come together. Not only are the transits able to be accurately predicted, but technological innovations in clocks and telescopes mean they can be accurately observed and measured as well."

For Wulf, the real value of the Venus missions lies not in their historical status as the world's first truly international scientific experiment, but in the fact they continue to have an impact on contemporary science, culture and society.

"We tend to talk about a global village as a 20th-century phenomenon, but the foundations were laid in the transit decade. It's the beginning of modern science as we understand it and the model for the international scientific cooperation, communication, experimentation and funding that continues to this day," she says.

For Dr Fernini, observations of the transit of Venus also have a currency that extends beyond their rarity: "The transit is an important way to present astronomy, physics and science to a wider public."

He hopes that other students, faculty members and even teachers and pupils from local schools will accept his open invitation to attend his observations on the UAEU campus on Wednesday, despite the early start.

Dr Fernini's observation will take place between 5.30am and 9.00am on Wednesday, June 6 at the Falaj Hazza football field, men's campus, UAE University, Al Ain. For more details see http://faculty.uaeu.ac.ae/ifernini.

Nick Leech is a freelance journalist living in Abu Dhabi.