Since the Mercury transit was such a fresh event, I thought to share the same material with Bobby that I had with Gwendolyn yesterday. It was wonderful to see Bobby's face light up when he first saw the tiny silhouette of Mercury appear against the backdrop of the Sun's photosphere and chromosphere in the video from the space.com website of the first few stages of the transit from an orbiting spacecraft. I was very impressed with how on the ball Bobby was with some of the Renaissance theories of the Universe, such as the heliocentric versus geocentric models of the Solar System, and the fact that at one point - not so long ago (relatively speaking) - the Earth was still considered to be flat. We spent some time talking about how boats appear to drop off the end of the Earth when they sail far enough away toward the horizon. Due to the fact that light travels in straight lines, on very clear days and with little turbulence due to air currents, or hazy weather, when a boat gets far enough toward the horizon, it will apparently disappear from view - this is not because it fell off the edge into nothingness, but because the Earth has significant curvature due to the fact it's spherical.