Venus last crossed the sun in 2004, shown here. (Mike Durkin/Flickr)

Scientists and space-heads have been buzzing about the event for weeks now, but MSNBC gives a great breakdown of why the rest of us should care.

For one, it's pretty rare. Venus actually makes the rounds in paired trips, eight years apart. Then there's a lull for either 105.5 or 121.5 years. We just saw one in 2004, and after today, it won't happen again until 2117.

And apparently it matters when the different edges of the planet cross the sun's edge. These help scientists calculate the details of our solar system, and for today's purposes, can help give a better idea when you should direct your gaze upward—using proper safety precautions, of course.

Read the full guide here. 

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