Nicole at Skepchick has links for how and when for this week in 2012. The Local Transit Times page on the Transit of Venus website reckons that for Sydney the details are as follows (and the Sydney Observatory reckons they’ve done their sums right):
Average Cloud Cover for June: 58%
ingress exterior Jun 6 08:16:09
ingress interior Jun 6 08:34:05
transit center Jun 6 11:30:12
egress interior Jun 6 14:26:23
egress exterior Jun 6 14:44:15
Notes on the data
Planetary transits start when the planet’s disk is externally tangent with the sun (ingress, exterior). From then, the planet may be discerned as a little black dent in the solar limb, gradually growing bigger until the entire planet is seen on the solar disk (ingress, interior). During the next five to six hours, the planet will traverse the sun’s disk until the planet’s disk will touch the opposite solar limb (egress, interior). The transit ends when the planet’s disk is externally tangent with the sun (egress, exterior).
For we Australians and New Zealanders, it’s one of those what-if history questions: if not for the 1769 transit of Venus where Captain James Cook was commissioned to take scientific observations from Tahiti, making for a neat stepping stone for an investigation of the Southern Oceans for evidence of the ‘postulated Terra Australis Incognita‘, how much longer might our islands have remained unknown to the Europeans? Which nation other than Britain might have discovered and settled us instead if Cook had been a less astonishing navigator/cartographer?