I've spent this week at the Sydney Writers' Festival in Australia, where I had the honor of giving the closing address on a topic of high local interest: the upcoming Transit of Venus. The rare passage of Venus across the Sun's face will be visible from all of eastern Australia, weather permitting, on June 6. Not only will locals get to see the six-plus-hour event in its entirety, but the history of their country is bound up with James Cook's voyage to view the 1769 Transit of Venus. After Cook completed his astronomical mission in Tahiti, he obeyed government orders to sail on to other southern lands, explore them, and claim them for the British crown. In the following century, with Australia in favored viewing position to see the transits of 1874 and 1882, observatories here purchased new telescopes and devised specialized cameras for the occasions. I've gotten so enthused discussing the June 6 prospects in Sydney that I need to keep reminding myself my own date with Venus is set for the day before, June 5, back home on the other side of the International Date Line. I'll be viewing the transit--the last one Earthlings will see till 2117--from the Mount Wilson Observatory in California.
The transits of the 18th and 19th centuries gave astronomers the means to gauge the distance from the Earth to the Sun. Although modern radar methods allow more precise Solar System measurements, the June event offers a unique opportunity to probe the atmosphere of Venus and to refine strategies for detecting Earth-like or Venus-like planets around other stars.
At the same time, amateurs the world over will get the chance to double-check the Earth-Sun distance in a new cooperative global enterprise.
The Transit of Venus app, available free, miniaturizes a shipload of expedition paraphernalia. Unavailable during the last transit, in 2004, the app enables anyone with the right eye protection and a smart phone to seize this once-in-a-lifetime opportunity.