Stephen reviewed terms learned thus far for the current unit and he made flash cards to use throughout the unit.

As always, I start each lesson by quizzing Gwendolyn on topics we have covered, either in the last class, or even further back in time. Today I thought it would be good to review what we have learned about the Solar System, so I started by asking Gwendolyn some questions. Let me say that Gwendolyn really knows the main planets in our Solar System. She is spot-on with their order from the Sun, and remembered perfectly that the only two planets without moons happen to be Mercury and Venus. Gwendolyn also remembered that the gas giants have large numbers of - identified -moons (around 50 or 60 for Jupiter and Saturn, some 10-30 for Neptune and Uranus). And we always have a giggle when we recall that Mars' moons are somewhat irregular in shape, and are often likened to potatoes. We watched a short NASA documentary on the planets, and at every moment I could, I paused the video to ask Gwendolyn questions to make her think about what was being said. As always, I got the feeling that Gwendolyn was truly engaged in our class.

Bobby was absent today.

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.

Stephen continued with his Stanford test today.

Since we had the 2016 Transit of Mercury yesterday, I thought it might be interesting for Gwendolyn to see some videos related to that event. These transits occur approximately 13-14 times per century, and basically involve the planet Mercury passing across the face of the Sun. The first transit of Mercury was observed in 1631 by Pierre Gassendi, some twenty or so years after Galileo Galilei pointed a telescope toward the skies. I took the opportunity to tell Gwendolyn a bit about Galileo, and the history of modern-day astronomy. Galileo, contrary to popular belief, did not invent the telescope, but he was the first to point this magnifying instrument toward the skies (we also looked briefly at the physics of lenses). What was so important about these first observations of transits was that the heliocentric model of the Solar System was still in its infancy, and seeing the perfect sphere of Mercury pass across the face of the Sun also consolidated the fact that Earth was, in fact, round, and not flat. In addition, some of the transit images we looked at were taken from orbiting spacecraft closer to the Sun, and so we could see the complex magnetic structure of the Sun's surface.

I understood that Bobby needed to go over certain concepts before next week's test, and one of them was seasons on Earth. Using the globe that is in his room, I showed how the tilt in the Earth's axis affects the amount of sunlight that impinges upon the surface, and in turn this determines whether the northern or southern hemisphere experiences winter (and the other hemisphere by definition summer). I started by reminding him that all planets not only orbit the sun, but also rotate about their own axes. All planets but one have an (arbitrary definition) up-down axis and when I asked Bobby which one did not he replied without hesitation Uranus (Bobby has a great memory). We then watched a short documentary on the bolide that crashed into the Russian steppes a few years back that was caught on several dash-cams. The size of that rock was some 17 yards across, not large enough to cause widespread damage, but sufficiently large to be spectacular in the sky and create a shock wave strong enough to knock people off their feet. This bolide is a larger version of what we know as 'shooting stars', which are in effect small grains dust that burn up in the atmosphere.

In our discussions on gravity, I thought it might be a good moment to introduce Bobby to the concept of the 'equation' in science. I asked him if he could come up with an equation and without hesitation he said E = m c^2. I spent a few minutes explaining the different terms in this equation, i.e. that 'c' is a constant representing the speed of light, and this number never changes; that 'm' stands for mass, and this is the input (as an important aside, Bobby was fully aware that 'mass' and 'weight' are two different things, the latter being the effect of gravity on mass); and the 'E' is for energy. We then moved onto the four fundamental forces of nature (electromagnetic, strong and weak nuclear forces, and gravity) - the first three act at short range, while gravity is a long-range force. After I introduced the equation for the force of gravity to Bobby - F = G (m1 * m2) / d^2 - and explained to him what the terms are (G the gravitational constant, m1 and m2 the two masses upon which the force acts, and d the distance between the two masses) I showed him what happens to the force if either or both masses increase (the force increases). I then asked Bobby what happens to the force if I increase the distance between the two bodies, and without hesitation he replied it decreases. Spot on!

Stephen created nutrition flash cards as an activity to show what he has learned thus far, and to use for studying for tomorrow's quiz. He also was able to poll students about a new healthy snack! He is checking to see if people can determine which snack is healthier. He studies the labels first, then checks with schoolmates.

Stephen started class with an online review game, and a new one showing the fat, sodium and oil content of different snacks in a fun way. Then he worked on brainstorming and beginning the writing for his healthy eating writing assignment.