Venus, the Best and Brightest

A historian makes the case for Earth’s closest neighbor.

Venus's transit in front of the sun in 2012 (NASA)
Editor’s Note: This article is part of the series “What Is the Best Planet?

I usually don’t criticize my colleagues in public but I would like to draw attention to two articles in The Atlantic—one by Adrienne LaFrance ‘Jupiter Is the Best Planet’ and the other by Ross Andersen who claims that Saturn is the best planet in the solar system. Honestly? They can’t be serious. Jupiter might be our largest planet but do we really want to say that bigger is better? Surely, size can’t be enough to win this cosmic competition.

And Saturn? The ringed planet is such a show–off. I admit, the first time I saw Saturn through a telescope, I was impressed. It’s a magnificently beautiful planet, but after a while beauty becomes a little boring. It’s a bit too superficial as a criteria and frankly, there is not much else to admire about Saturn. It’s just a gas giant, way out in the distance.

Consider Venus instead, a planet named after the goddess of love. Who cares if it’s a little hot up there? Who cares if its surface is hidden behind thick clouds composed of sulphuric acid? In his plea for Saturn, Ross Andersen writes that the inner planets are boring, but I beg to differ. Venus is the most fascinating of all planets: from her (yes, Venus is a she) importance to the ancients, her brightness in the sky, her role in triggering the first international scientific collaboration, and the lessons we might learn from her about the runaway greenhouse effect. Venus is such a great planet that I have even written a book about her: Chasing Venus: The Race to Measure the Heavens.

But I’m getting ahead of myself—let me make my case for Venus properly.

The ancient Babylonians called her Ishtar, for the Greeks she was Aphrodite, and for the Romans Venus—goddesses of love, fertility, or beauty. Venus has fascinated humankind for millennia. She is the brightest star in the night sky and even visible during a clear day. Some saw her as the harbinger of morning and evening, of seasons or portentous times. She reigns as the ‘Morning Star’ or the ‘Bringer of Light’ for 260 days, and then she disappears to rise again as the ‘Evening Star’ and the ‘Bringer of Dawn’—which is the reason why many cultures thought she was not one but two planets. Not so for the Babylonians, who recorded her movements for a period of 21 years on the Venus Tablet of Ammisaduqa around the mid-seventeenth century B.C.E. The Mayans also regarded Venus as important and she was part of their religious calendar.

But enough of the ancients. Venus continued to be significant for later generations too. She played a role in the acceptance of Copernicus’s heliocentric model of the solar system. When Galileo saw Venus goes through phases like the Moon, he noticed that sunlight could only have interacted with it in this way if the planets moved around the sun.

In the 18th century, Venus, the ‘bright queen of the sky’ held the key for the size of the universe. No other planet can claim such an accolade. In the midst of the Seven Years’ War, Venus initiated a scientific race across the world—a race that united hundreds of astronomers from dozens of countries. As the war tore Europe and its colonial possessions apart, scientists ignored political, national, and religious borders in their search for knowledge. They traveled across the globe to far away places to observe the transit of Venus, one of the rarest astronomical events.

During the transit, Venus moves between Earth and sun and is visible for about six hours as a perfect black dot moving slowly across the burning face of the sun. The planet, which is almost as big as our own, is dwarfed by the immensity of the sun. The transits occur in pairs—eight years apart—but then it takes more than a century for Venus to do her show again. (The last transit was on June 6, 2012 and if you missed it, you really have missed your chance, because the next one will only be in December 2117).

For astronomers in the eighteenth century the transits of 1761 and 1769, Venus was the celestial yardstick with which to measure the size of the solar system. If they could only measure the exact time and duration of the transit, they would get the data they needed to calculate the distance between Earth and sun, and by extension the dimensions of the solar system—the holy grail of astronomy.

The only trouble was that several people at different locations had to measure the rare heavenly rendezvous. If they viewed the transit from different places as far apart as possible, they would observe Venus traversing the sun along a slightly different track. With the help of relatively simple trigonometry, these different tracks (and the differences in the duration of Venus’s march across the sun) could then be used to calculate the distance between the sun and Earth.

This is where the adventure stories begin. Years in advance of the transit, astronomers traveled to the far corners of the globe to be ready for the rare celestial encounter, risking their lives to catch a glimpse of Venus. It was an audacious undertaking at a time when clocks were still not accurate enough to measure longitude precisely, and when a letter posted in Boston would take two to three months to reach London.

The names associated with these Venus observations read like a roll call of the Who Is Who in the eighteenth century: Benjamin Franklin was involved, as were Charles Mason and Jeremiah Dixon who measured the Mason–Dixon Line in between their transit observations. King George III built a special observatory for Venus and Catherine the Great dispatched eight expeditions across her vast empire, extending as far east as Yakutsk. Captain James Cook was sent on the Endeavour to watch the transit in Tahiti while others traveled to the remote island of St. Helena. Dozens of astronomers boarded ships, carriages, and sledges to travel to the outposts of the known world—from the Arctic Circle to Tahiti; from Siberia to India and from Cape Town to Jakarta. Laden with instruments that weighed half a ton, the astronomers traveled amongst warring armies, tropical storms, or treacherous ice. Like invisible threads, their voyages created a web of knowledge and collaboration across the globe.

There was David Rittenhouse, for example, America’s first astronomer, who built himself an observatory on his farm in Pennsylvania and instructed a great many others how to observe the transit. But he was so excited when Venus finally appeared on the day of the transit that he fainted, missing the beginning of the most important scientific event of his life. Or the British astronomer William Wales, who woke up every morning with his bedding frozen stiff against headboard of his bed (which was covered in a layer of ice) in his hut in Hudson Bay despite having said in his job application that he “was preferring a voyage to a warmer climate.”

Many astronomers endured unbelievable hardship—from life–threatening diseases to bloody battles—all for the elusive distance between Earth and sun. There was the tragic Guillaume Le Gentil who chased Venus for eleven years—from France to Pondicherry, Mauritius, Manila and back to Pondicherry—but in the end failed to take a single useful measurement. Or Chappe d’Auteroche who travelled 4,000 miles to Siberia for the first transit and then to Baja California for the second, where he viewed Venus from a typhus–infested Jesuit mission. Delirious with fever, Chappe died hours after recording his final data.

Others were luckier and dispatched their results to the scientific societies in the learned centers in Europe where the data was collected. During each of the two transits—in June 1761 and 1769—around 250 official observers at more then one hundred locations measured Venus’s path across the sun. There were problems, bad weather, uncertainties, and inaccuracies but amazingly the astronomers calculated that it was between 93 and 97 million miles, very close to today’s accepted value of just under 93 million miles.

Pretty impressive, but the most important result was that an international community of scientists and thinkers had worked successfully and peacefully together. The race to observe the transit of Venus was a pivotal moment in a new era, one in which humankind tried to understand nature through the application of reason. It was the most ambitious scientific enterprise ever planned and the transit astronomers are the forefathers of all Big Science Projects today—and all because of the very best planet in our solar system.