Last chance to see 'hole in the sun' for 105 years!

Maybe you'll be here in 105 years. If so, good for you. And go buy some real estate.

However, for the rest of us, this Tuesday will present a chance to see something that will never happen again in our lifetime. And possibly your children's. Though actually seeing it is going to require some extra protection.

It's called the "Transit of Venus," an extremely rare astronomical event in which Venus passes between the earth and the sun at just the exact right angle so that the planet is silhouetted against the solar disk -- like someone punched a hole in the sun. As the day goes on, the tiny black dot that's our solar system's second planet will traverse the sun in an arch.

And then it won't happen again until 2117. And if you're thinking, "That sounds like something we should commemorate!" well here you go: T-shirts are already available!

The Transit of Venus occurs four times every 243 years. The last one was in 2004, but Tuesday's will be the final transit of the century. In fact, Halley's Comet will be back before Venus criss-crosses the sun again.

More than just an awesome spectacle, the transit of Venus has also played a significant role in nothing less than helping determine the size of our solar system. During the pair of transits which occurred in 1761 and 1769, scientists dispatched around the world to record the event from observatories and living room telescopes in locations including France, Austria, Tahiti, America and Siberia.

They each timed the duration of the transit from their vantage points to help calculate the distance from the earth to the sun. Turns out many of their observations were flawed due to a phenomenon called "the black drop effect," (and some poor fellow also spent eight years trying to observe the thing and lost his wife and was presumed dead in the process) but the research laid the groundwork for learning the scale of the solar system.

The full duration of Venus' trip across the sun is about six hours and you can visitTransitOfVenus.nl to check your local viewing times.

The same site also has some very handy advice on how to avoid destroying your retinas trying to see the thing. It's pretty long and detailed though (sample sentence: "A safe solar filter should transmit less than 0.003% (density ~4.5) of visible light and no more than 0.5% (density ~2.3) of the near-infrared radiation from 780–1400 nm.") so we'll just advise using a pinhole projector or creating a means to view a reflection of the event.

Then jot down your detailed viewing instructions so that your kid's kid can tell their kid how to view the next transit of Venus in 2117. (source)