Some events in astronomy are like a fine glass of wine and the June 5, 2012 transit of Venus across the face of the Sun was one of those fine moments. It was made even more so by a stubborn cut-off storm system over the Northeast U.S. that was unusual for June and came at the worst possible time. Against all odds during that week long chilly storm came a break at the right time allowing a rare chance to sip that fine wine, and savor a rare astronomical moment of a lifetime.
What is the big deal about the dark dot of Venus against the Sun, especially when many of us saw it eight years prior on June 8, 2004? First off it was an unusual sight and something that will never be seen again in our lifetimes. The next Venus transit is December 11, 2117, but the next one visible from this part of the world is not until December 8, 2125, so that gives the added sense of mortality and a greater appreciation of the event. Another big deal about a Venus transit is the same feeling that makes lunar and solar eclipses so special: the 3-D perception of our place in the Solar System and in the case of the Venus transit, how small Venus and Earth are compared to the Sun. Venus and Earth are almost the same size, yet Venus appeared so tiny compared to the Sun it was crossing; the Sun is around 93 million miles from Earth, but Venus was only about 26 million miles from Earth! The slow progression of Venus across the Sun also gave the feeling and proof that Venus indeed orbits between the Sun and Earth. The planets look like another star against a starry night sky giving no sense of depth perception even though we know otherwise, but a transit gives the sensation of depth.
The Venus transit has scientific applications, both historic and current. By timing the transit from widely separate regions on Earth and applying Kepler's Law of Motion, it is possible to calculate the distance from the Earth to the Sun. That was vital back in the 1700s and 1800s in determining the size of the Solar System. This motivated Captain Cook to sail to Tahiti in the South Pacific in 1769 to observe a Venus transit. Observing the Venus transit last year was like looking back in history and at something that has only seen seven times since the era of Galileo. Venus transits are indeed rare and yet the technique can be applied in the modern era. Scientists are discovering planets around other stars by using the transit method. When a planet passes in front of a star, the amount of light from the star drops a tiny amount. Our Sun was a tiny bit dimmer during the Venus transit, but way too tiny to notice without sensitive equipment. The Kepler spacecraft may have found over 2000 of these exoplanets, planets that orbit other stars, by observing transits. An astronomer on another planet in orbit around a distant star could discover Venus in our Solar System by watching it transit the Sun, and all the other planets including Earth if the alignments were favorable.
If you observed the 2004 and/or the 2012 transits of Venus, you can now gain a greater appreciation of the significance of a transit and gain a better perception of your place in the Solar System. If you missed the Venus transits, there is still a consolation prize, weather permitting. On May 9, 2016 Mercury will transit the Sun; it will be visible from start to finish, from 7:12 A.M. until 2:42 P.M., lasting 7 1/2 hours, so make no excuses not to see a transit this time!