This lecture was initially prepared with one specific goal in mind: to explain the principles of the Special Theory of Relativity to an audience with no college level physics knowledge and at the same time solve the problem of the twin paradox, one of the classic problems in Special Relativity theory. It was initially presented at the Portuguese Conference of Physics Students (Covilhã, Portugal, 2001) and in the International Conference of Physics Students (Dublin, 2001), it was then presented to a wide range of audiences, at several high schools and in several editions of the Physics Week, organized by the Physics Student's Association of Instituto Superior Técnico, an engineering university in Lisbon.

On Earth Day (April 22nd) I gave a lecture at one of Lisbon's high schools about our home planet. In it I try to show a side of Earth we seldom think about, its size and the size of the continents, oceans and countries. I then proceed to explore the Solar System, then the Milky Way, our galaxy, and finally the whole Universe. The main purpose is showing that, on one hand, our planet is huge when compared to what we know of it, and on the other hand it's insignificant when compared with the emptyness of space or the size of the starts.