March 7th, 2011
Episode 255 of 470 episodes
Since the planet Venus is closer in to the Sun than Earth, there are rare opportunities to see it pass directly in front of our parent star. This is known as a planetary transit, and thanks to the geometry of the Earth and Venus, they only happen a couple of times a century. The transits of Venus have been used by astronomers to unlock the scale of the Solar System, and there’s another one just around the corner.