Tuesday was the last opportunity I’ll ever have to see the transit of Venus with my own eyes, and Alaska is one of the places where it was (theoretically) visible from beginning to end. Local astronomers with properly shielded telescopes were set up by the Noel Wein Library in Fairbanks, so since the sun was actually shining around 2, I took off to see the fun.
I said theoretically because while the sun was up for the duration of the transit, and the transit was visible (unlike a solar eclipse) from anywhere that the sun was visible, it’s been cloudy most afternoons. I set out with more hope than expectation, as towering clouds were visible in all directions. (It had hailed the day before.)
I’m not going to repeat in detail the reason why transits of Venus are rare—the Wikipedia article I’ve linked to does a good job of that. Basically, the orbit of Venus is inclined to the orbit of Earth by 3.4°, which means that Venus appears actually to cross the sun only when both planets are very near the line of nodes, the line defined by the crossing of the two orbits, at the time Venus comes closest to Earth. Last Tuesday was the last time this century that this will occur.
By the time I made it to the library, the lawn sprinkled with telescopes was sunlit – most of the time. Clouds were scudding back and forth over the sun, and a thunderhead was towering to the east and headed our way. (Yes, thunderstorms often move from east to west up here.) I got a look at the sun through a properly filtered reflector during a break in the clouds, and later managed a photograph of a setup where a small telescope was focused on a mirror that produced an image on a white card. Literally minutes later the sun was covered with dark clouds.
I’m glad I had a chance to see this. I’m not a big observer of astronomical events, but I got to watch the total solar eclipse in 1963, any number of lunar eclipses, the partial eclipse last month (via a pinhole camera) and now the Venus transit of 2012. Wish I could find my solar eclipse photo – it was spectacular.