Right, so the scientific importance behind the transit has to do with the question of how we manage to measure things in space (like the distance between the Earth and Sun), but have you wondered exactly how it is that scientists manage to measure even greater distances, like how far away other galaxies are, or even how old the universe is? Well, wonder no more because here's a quick little introduction to the general idea:
And if you want the more serious treatment about how scientists have figured out the age of the universe, you might want to check out In Our Time, with Melvyn Bragg.