The Union Recorder

June 6, 2012

The transit of Venus

Beate Czogalla
The Union-Recorder

MILLEDGEVILLE — June 5, 2012. Yep, that’s today. Today is one of the most anticipated days of the century for many astronomers and hobby photographers alike: the planet Venus will pass directly in front of the sun, and its transit will be visible from most of Earth’s inhabited regions.

So what, you might think — Venus is a planet, closer to the sun than Earth, so wouldn’t it pass in front of the sun’s face at least once a year?

Technically, yes.

But due to the difference in inclinations of Venus’ and Earth’s orbital planes you can actually only observe such a transit about every 100 years (the next one won’t be until 2117). Here in Milledgeville it starts at 6:09 this evening. It should be a no-brainer, but it bears repeating: do not under any circumstances attempt to observe this transit with the naked eye. Not only is Venus too small to be picked out in the sun’s glare, the sun will also fry your retinas and cause irreversible damage to your eyes. So unless you have a good pair of welding goggles handy (be sure they have no. 14 shade glass) you’re better off watching it online and being perfectly safe. There will be webcasts, live reports from all over the world, and there are plenty of ways to participate safely. Here is the link with all the info:

Venus transits always occur in pairs, about eight years apart, so if you missed the one in 2008 now’s your chance!

So what is the big deal, anyway?

If you’ve ever wondered how far away the sun really is, or how big our solar system might be, a transit of Venus helped answer that question before the advent of radar astronomy. While we have very accurate means of measuring those distances now the proven mathematical system of parallax came amazingly close. If you observe a cosmic event such as a transit from points far away on Earth (as long as you know the distance between those points) some simple trigonometry will allow you to calculate how far away the sun is.

The famous explorer James Cook was dispatched to Tahiti in 1761 to observe the transit of Venus, which also brought about another unexpected discovery. What messed up the data then was the observers’ inability to determine the precise start and ending of the transit due to Venus’ atmosphere, which cause distortions of the sun’s edge, first discovered by Russian astronomer Mikhail Lomonosov. Up until that point nobody had even suspected that Venus might have an atmosphere, but it was confirmed in the 1874 and 1882 transits. At this point astronomers were trying to capture the event with photography for the first time, and excitement ran high, even though those first attempts produced grainy and largely useless pictures. Still, they were able to pinpoint the crucial Earth – Sun distance to within 500,000 miles. A transit of the asteroid Eros (yes, the one that now has the NEAR Shoemaker spacecraft sitting on it) in 1931 refined this measurement to within 3,000 miles, but it wasn’t until the 1960s that radar measurements measuring the distance between Earth and Venus helped provide an accurate number at long last.

This doesn’t mean that the method of calculating distance via parallax is out. The Kepler spacecraft uses it to find new extrasolar planets – and what if you want to measure even greater distances, say, between galaxies, where a mile here or there really doesn’t matter? Good old trig to the rescue!

So why are we still getting excited about the Transit of Venus, even though we’ve long answered the question it was supposed to provide an answer for? How about: because it’s just cool? Or because it won’t happen again in our lifetime? Or how about the fact that this event captures the public’s imagination, and people talk about science and the history of science, and they look up the principle of parallax, and James Cook and Mikhail Lomonosov?

The Transit of Venus is not only a rare spectacle — it is also a unique opportunity to celebrate the ingenuity of the human scientific mind and the creativity of people who look at our universe and want answers, and then get to work and figure them out.

Watch a short video about the Transit of Venus here:

Beate Czogalla is the Professor of Theater Design in the Department of Theatre and Dance at Georgia College & State University. She has had a lifelong interest in space exploration and has been a Solar System Ambassador for the Jet Propulsion Laboratory/ NASA for many years. She can be reached at