The first to occur is the near-total eclipse of the sun. Coming May 21, 2012 it will be a near-total event in the Black Rock Desert less than 100 miles north of me. Yes, it's the same desert where the annual Burning Man festival occurs every Labor Day weekend. Even here in the big city, the eclipse should be pretty spectacular. Of course, DO NOT LOOK AT THE SUN if you are thinking of witnessing this spectacle yourself. Hie your eyes to a local university, community college or even a high school with an astronomy class to find if they are going to have their telescopes with appropriate filters fired up.
Even if you don't live in northern Nevada, you don't have be the target of a Carly Simon song and fly your Lear Jet to Nova Scotia to see it. And we can only hope your experience is better than that of Monty Python's too. Visit NASA's website to see how much eclipse you get in your area. Below is a screen shot showing the details at the best closest spot to me.
Interestingly, a couple of hundred years ago, the transit was a way for astronomers to measure the size of the solar system. How? Observers from two disparate locations on Earth would see two distinct paths of Venus across the sun. Using the slight difference in the length of time it takes Venus to move from one edge of the sun to the other, they were able to calculate the distance from earth to the sun, and thus the size of our solar system. Once again, science and math charging to the rescue.
Again, DO NOT LOOK AT THE SUN - not even for just a second. I cannot stress this enough. You WILL damage your eyes, and I will take it as a personal affront, since you will no longer be able to easily read the pithy wisdom of my words.
For gobs more information on the transit, visit transitofvenus.org. Alas for my hordes of Brazilian, Argentinian, and Chilean readers, the transit will not be visible to you at all.