Story by Paul Wood
To measure it, people once said, was to undertake “the noble experiment”— and that experiment sent Captain James Cook sailing into the Pacific for the first time. No one saw it throughout the entire twentieth century, and the next one won’t come for another 105 years. So for your lifetime, this is it: The Transit of Venus. And this time Hawai‘i happens to be front row center for the entire thing. The moment: Tuesday, June 5 from about ten minutes after noon until just before the sun drops into the sea.
To understand the Transit of Venus, remember your schoolkid- days planet lore— that Venus orbits between us and the sun. Rarely but regularly, we can watch the Earth’s sister drift across the face of the sun, a vivid black dot against our star’s hyper-blazing hugeness. These transits happen in pairs eight years apart, with more than a century intervening between pairs; the first of our current pair took place June 8, 2004. Only six transits have occurred since the invention of the telescope.
Who cares? All of Europe did once. Expeditions went forth in every direction to measure the precise seconds of the transit; the 1761 transit, for example, was observed by 176 scientists at 117 different spots across the globe. The purpose of these expeditions was to collect data that scientists could use to determine the exact size of our solar system.
Quick astronomy lesson: In 1534 Copernicus published his discovery that the planets orbit the sun in fixed order. Several decades later Johannes Kepler, using the mathematics of his brilliant mentor Tycho Brahe, figured out the relative distances of the planets from each other. But no one had a single, precise measurement that could be used as an exact celestial yardstick. If someone could figure out the distance between Earth and the sun, for instance, that number could be used to measure lots of other things — for example, the precise longitude of a sailing ship wandering around the Pacific. It was Edmund Halley (of Halley’s Comet fame) who in 1716 suggested that measuring the Transit of Venus could once and for all enable scientists to fix astronomical distance. But the transit would have to be measured with fine precision at places all over the planet. Halley’s idea launched multiple expeditions, including that of then-Lieutenant James Cook, who sailed to Tahiti aboard the HMS Endeavour to observe the 1769 transit.
When the transit came around again in 1874, the British were still dissatisfied with the accuracy of their measurements. So they again sent scientific expeditions across the globe. One came to Honolulu, and King David Kalakaua, seven months into his reign, greeted the party with great ceremony and set them up on a plot of land south of Punchbowl. The British group also set up auxiliary stations at what’s now Hulihe‘e Palace in Kailua-Kona and at Waimea, Kaua‘i. Those nineteenth- century scientists, in their beards, white suits and pith helmets, were not the best of guests: They griped about the rain, the mosquitoes and what they saw as the intrusive curiosity of Kalakaua, his court and his people.
By this time Americans were observing the transits, too. William Harkness, director of the US Naval Observatory, wrote in 1882: “We are now on the eve of the second transit of a pair, after which there will be no other till the twenty-first century of our era has dawned upon the earth. … What will be the state of science when the next transit season arrives God only knows.”
This time around, scientists are hoping that the transit’s slight diminution of the sun’s glare (one-tenth of one percent) will help them locate planets in faraway solar systems. As for you— well, science in its current state has provided a free iPhone app that will allow you to participate in the next noble experiment and help measure the transit yourself. Of course Venus is pretty small, and you don’t want to laser-fry your corneas— so make sure you’ve also got a telescope and eye protection equal to a hundred Maui Jims.