Tomorrow will be the last chance for anyone currently living on Earth to witness a rare celestial spectacle...the Transit of Venus.
The transit takes places when the planet of Venus passes directly between the Earth and the Sun, and can be seen as a dark ball crossing in front of the sun. The next transit will not take place until the year 2117, meaning this your last opportunity to witness the unique event, (unless you plan on having your head cryogenically frozen so you can be brought back to life some years into the future).
The transit will commence in North America in the hours just prior to sunset on June 5, with a large portion of the United States being able to view the event, weather conditions permitting. People in Asia, Australia, Africa and Europe will be able to witness the transit on June 6.
You will need a special filter to view the transit, as one should never look directly at the sun which can cause severe eye damage. Transits are considered the rarest of predictable celestial phenomena, occurring every 243 years, with a "twin" transit taking place 8-10 years after the first. (Tomorrow's twin transit took place in 2004.)