~Exploring the 18th Century ~

There was one figure in history that could be labeled as the Godfather of the Transit. Without even witnessing the event, scientist Edmund Halley realized that if the Transit of Venus was observed from different locations on the globe, the parallax affect could be used to accurately calculate the distance between the Earth and the Sun (AU). He originally got this idea from examining the Transit of Mercury, when he was sent down to St. Helena’s to study it. Halley, in St. Helena’s, was able to take reasonably accurate measurements to compute the AU; but he recognized that the Transit of Venus would provide a better parallax from which the Earth-Sun distance could be measured to a greater precision.

BOX 1: WHAT IS SOLAR PARALLAX AND HOW WAS IT USED?

Parallax is the apparent displacement or the difference of position of an object when it is seen from two different locations. This effect can be applied on the calculation of the Astronomical Unit by measuring the shift in position of Venus against the sun in the background.

Even though Halley did not live to see the Transit of 1769, in 1716, Halley made a detailed plan for future generations of scientists to follow so that the AU could be calculated. There were a few crucial pieces of data that were needed to make Halley’s plan a success:

The Transit had to be observed from at least two different positions on the globe.
For each position, the longitude and the latitude had to be determined.
From each location, the exact time that Venus made first contact with the Sun (also known as Interior Contact of Ingress) and the exact time that it came out of Transit (Interior Contact of Egress) had to be recorded. These timings were required to be accurate to the very second; otherwise they would be useless as they would give an imprecise AU value (if computed).

Even though the Transit of 1761 was beyond Halley’s lifetime, in 1716, Halley formulated a plan that revealed the exact calculations which were needed to compute the AU, as well as the best places on the globe from where the Transit could be observed to give the best data values.

Although his plan seemed simple, we must understand that the technology available to scientists in that era was limited, and the actual feat of getting good data was close to impossible. Even then, the Transits of 1761 and 1769 were met by great excitement by the scientific community. Preparations for the phenomenal event had been sparked decades before, and a global emphasis was placed on using the rare occurrences to their optimum potential.

The first problem that scientists faced was that the locations in the world which were proposed by Halley were spread throughout the globe and many were still inaccessible or inhabited e.g. South Africa, Siberia, North and Central America, the Indian Ocean and the South Pacific. Longitudes and latitudes that were needed were not impossible to determine, but could only be done by highly-skilled astronomers and it took months to make careful calculations. Basically, to obtain the necessary data meant a lot of travel, and travel was difficult in those times. Long and difficult journeys aboard wooden ships were life threatening as well as expensive, and were measured in months and years… not hours, like we are able to do today. Also, observers had to reach their destination, find a suitable location from where to observe and then set up the equipment before and after the Transit. This meant that teams of astronomers who were dispatched throughout the world to observe the Transit of Venus in 1761 and in 1769, devoted years to prepare and study the phenomenon at the risk of losing their lives.

Not only that, but the world was united during these preparations, as a global effort was required to coordinate journeys, gather, transfer and process data. The Seven Year War that stretched in Europe from 1756 to 1763 did not comprise the scientific effort that was being placed on observing the Transit of Venus. Despite strong hostilities between neighboring countries, scientists were allowed thoroughfare between lands as well as protection against the violence.

Yet, more problems arose, for after years of preparation, Mother Nature still had the last word. During the precious 7 hours when the Transit occurred, cloudy weather or other unfavorable conditions (like nearby warfare, or breakdown of equipment) made observations impossible to carry out or rendered them completely useless because of a lack of accuracy. The Transit of 1761 allowed a scientist named Mikhail Lomonosov to prove that Venus had an atmosphere, which could be seen as a blurry halo around the planet. It was this same halo – Venus’s Atmosphere – that made observing the Transit a misery for astronomers, as they slammed into their first brick wall: the Black Drop Affect. Few were able to get good data from the Transits of 1761 and 1769.

BOX 2: WHAT IS THE BLACK DROP AFFECT AND WHAT PROBLEMS DID IT CREATE?

The black drop effect is caused by refraction of light through an atmosphere or steam which makes the original subject seem larger than it actually is. Through the sulfuric atmosphere of Venus, the sun's rays are refracted and they appear to form a halo around Venus. This makes it hard to determine when the ingression (first contact in a Transit with the edge of the Sun’s limb) and egression (second contact that marks the end of the Transit) occurs. The black drop affect did not allow scientists to get accurate timings of the transit, and hence time, effort and money invested in an expedition was wasted because of the imprecision created by this natural, uncontrollable factor.

However, there was one notable expedition that was launched to observe the Transit of Venus that not only obtained good data, but had a great cultural and political affect.

In 1768, Captain James Cook set sail form Plymouth aboard the H.M.S Endeavor, accompanied by astronomer Charles Green and naturalist Joseph Banks. Armed with Gregorian reflecting telescopes, astronomical quadrants, clocks, pocket watches, tent observatories and other fiddly brass instruments; the purpose of Cook’s mission was designated by the Royal Society of London... and it was mostly a scientific one. Yet, politics did creep into the picture as Cook had also been sent to explore the South Pacific in search for the mythical southern continent.

After more than 7 months at sea, Cook and his crew landed at Tahiti, where they set up their equipment at a high location that is still known as “Point Venus”. Though Charles Green and his companions (including Captain Cook) had to endure theft of instruments, they got better timings than anyone else had in that era. However, they had been hoping for an error margin of 2 seconds, but the black drop affect, regardless of the effort Green put into choosing his instruments, widened the margin to almost 10 seconds.

Still, the trip had been successful in producing excellent data. Not only that, Cooks journey impacted the South Pacific islands, allowed different cultures to meet and led to the discovery of the mystical southern continent (which includes New Zealand).

Therefore, it is easy to conclude that Cook’s legendary journey had not only impacted the international scientific community by producing valid data from which the AU could be calculated, but had triggered the meeting of cultures in our historical timelines that would eventually lead to the globalization which exists today.