As I mentioned back in March, tonight one of the rarest predictable astronomical events will occur – a transit of Venus. [I’m washing my hair! – Ed] What hair? ANYhoo… Since the invention of the greatest human innovation, the telescope, at the beginning of the 17th century, not by Galileo, there have been only 7 such transits. The next time it will happen will be on 11 December 2117.
The BBC’s spaceman, Jonathon Amos, has a good report on the historical and contemporary significance of the transit.
The phenomenon has particular historical significance. The 17th- and 18th-Century transits were used by the astronomers of the day to work out fundamental facts about the Solar System.
Employing a method of triangulation (parallax), they were able to calculate the distance between the Earth and the Sun – the so-called astronomical unit (AU) – which we know today to be about 149.6 million km (or 93 million miles).
This allowed scientists to get their first real handle on the scale of things beyond Earth.
The first person to predict a transit of Venus – the 6 December, 1631, event – was Johannes Kepler, but he died before it occurred.
Jeremiah Horrocks, the young English astronomer, was probably the first to record the phenomenon when he and his friend, William Crabtree, made separate observations of the passage on 24 November, 1639.
By the time the transits of 1761 and 1769 came around, they had become major scientific events. Expeditions were despatched all over the globe to get the data necessary to calculate the AU.
One such expedition was undertaken by Captain James Cook, whose epic voyage in the Endeavour took in the “new lands” of New Zealand and Australia.
Transit-hunting has proven a successful method in the hunt for exoplanets.
And from SunEarthDay on YouTube, part1 of a 6 part series of clips highlighting the history and the science behind the transit and the culture and history of Hawaii. As you’d expect, one of Those [Royal Society] Guys makes an appearance…
Adds Here’s a stunning short video from NasaExplorer using images from LASCO C3 coronograph on board the SOHO spacecraft.
Update Live video stream from NasaTV.