An event like last week’s solar transit of Venus tends to make a splash in our neighborhood in Baltimore, which is about a mile up the road from the Space Telescope Science Institute (STSI), headquarters of the Hubble Space Telescope.

On Tuesday, while astronomers in a secure room in the basement of STSI were busy training Hubble on the moon, using it as a mirror to study the light bouncing off Venus during the transit, amateur astronomers and curious locals gathered in the shadow of the Eisenhower Observatory next door, in order to see the transit with their own eyes.

Why?

Good question.

These days, you can get an infinitely better view of a solar event like the Venus transit sitting in front of a computer than you can by peering at the sun through a welder’s lens, or looking at a projection on a piece of white paper. Observatories across the globe — and even in its orbit — broadcast the transit live.

There’s a strange sort of psychology at work in viewing these rare natural phenomena. Take Halley’s comet. I was in college when Halley’s comet last swung by the earth, back in 1986. But even as a callow, self-involved, nineteen-year-old, I felt that if I didn’t see it, or, more importantly, make an effort to see it, I’d be missing out on something important. After all, the comet wouldn’t be back again for 75 years. You didn’t have to be an actuary to know that chances were pretty slim you’d be around in 2061 for the next viewing.

Halley’s comet is pretty well known. Certainly a lot better known than a Venus transit.

So what was the big deal?

Aside from being even rarer than Halley’s comet, the Venus transit has, over the centuries, played a crucial role in the history of science.

By the 17th century, mathematicians and astronomers had a good enough handle on the relative orbits of the Earth and Venus to be able to predict the transit with some accuracy. In 1627, Johannes Kepler predicted that there would be a transit in 1631. This was an incredible feat of mathematics, considering that Venus transits happen in pairs separated by eight years, with a good 120 years or so between pairs.

Kepler’s prediction suggested a method for settling one of the burning questions of the day: how far was the earth from the sun? By observing the Venus transit from two places on earth — the farther apart the better — astronomers would be able to make a pretty good estimate of the sun’s distance, using a phenomenon called “parallax.”

You use the parallax phenomenon every time you look at something with both of your eyes. The few inches that separate the left eye from the right give human beings the ability to perceive depth.

Depth perception is an artifact of the human mind, but it’s based on a simple physical truth: two observations of the same thing, taken from different locations, make it possible to calculate the distance between the observers and the thing.

The 1631 transit was a bust, mainly because it wasn’t visible from Europe (unfortunately, Kepler’s calculations weren’t accurate enough to predict that). But all eyes were on the sun eight years later for the 1639 transit, which was carefully observed and recorded by two English scientists, one of whom used his observations to make the first tentative calculation of the sun’s distance.

That first calculation was pretty far off, but it was the most accurate guess to date. By the time the next transit rolled around in 1761, Europeans had conquered the seas. The observation of the 1761 transit was one of the first international scientific collaborations. Astronomers in Siberia, Norway, Madagascar, and Newfoundland trained their eyes on the sun. A pair of English surveyors named Mason and Dixon contributed precise observations from the southern tip of Africa.

Eight years later, the Royal Navy and the Royal Society dispatched a young captain named James Cook to the South Pacific to observe the transit. (And also, as an added bonus, to report on any strange and interesting lands he happened to encounter, which included what became known as Australia and New Zealand.)

Those transits produced better calculation of the sun’s distance, and the transits that followed in 1874 and 1882 produced even better ones.

But something happened between 1882 and the next transit, in 2004: human beings extended their reach into space. Radio telemetry using space probes made parallax calculations obsolete.

Even so, there’s still plenty to be learned from a Venus transit. The purpose of last week’s Hubble observations was to hone our ability to study planets in remote solar systems.

Who knows what the transit will teach us in 2117? I’m going to go out on a limb and say that I probably won’t be around for it. But I’m grateful that the overcast sky cleared at 6PM on June 5th, 2012, so I could spend a few minutes with my wife watching a little black dot crawl across the face of the sun.

We held hands. It was romantic.

 

This column was published in the Perry Co Times on 14 June 2012

For more information, please contact Mr. Olshan at writing@matthewolshan.com