I was impressed with how much information Gwendolyn had retained from last week's class! We reviewed the three types of missions and rockets from the early space program, and Gwendolyn remembered each one and how many crew they carried (Mercury = one astronaut, Gemini = two, Apollo = three). We stepped even further back, and looked at the history of aviation. To think that in only 66 years we went from the Wright brothers' hop-skip-and-a-jump to rockets to the Moon. Along the way, we discussed the pioneers of breaking the sound barrier (Chuck Yeager springs to mind) and how people at the time did not even know if a plane would come structurally undone or not if they went faster than the speed of sound. Gwendolyn asked many relevant questions on the nature of sound, and what does 'the speed of sound' mean, so next Tuesday we'll look further into this topic.

One of the topics that appears to interest Bobby is the scale of the Universe. We found a short documentary that we had not yet seen that started with a view of the Himalayas, then expanded outward to show the satellites that orbit Earth, the planets, the Solar System in the Milky Way, then all the galaxies all the way out to about 13.7 billion years ago when we see the echoes of the Big Bang in the form of the cosmic microwave background. As always, I stopped the video at appropriate places to discuss the concepts involved, and to answer Bobby's questions.

In order to understand black holes, it's necessary to be familiar with the concept of gravity. And one way to familiarize oneself with gravity is to explore space flight. In order to escape the enormous gravitational force of the Earth (relatively speaking - the force is strong for us who are stuck to its surface, but falls off inversely with the square of the distance, i.e. double the distance and you reduce the force of gravity by four) we need to supply rockets with enormous amounts of fuel. As always, Bobby asked the sharpest questions, including what would happen to the oceans if the Earth suddenly lost its gravity (not that that would happen, but Bobby's question on the hypothetical scenario was thoroughly amazing).

We started class with the history of human space flight in a (very small) nutshell. The Mercury mission (smaller rocket) carried one person into suborbital and then orbital flight that lasted several hours. The Gemini missions (larger rockets) carried two people into Earth orbit for more complex operations that would last for several days (up to nearly two weeks in one case). The Apollo missions (largest rockets, amongst which the majestic Saturn V) took three people to the Moon, two who descended onto the surface in the lunar module, the third stayed in orbit around the Moon in the command module. The reason for the ever-larger rockets is the fact that we need to escape Earth's gravity to enter into Earth orbit and to sail to the Moon. We talked a lot about gravity, and what effect the weaker gravity of the Moon (1/6 that of Earth) has on people walking on the Moon. We watched a short video with real footage from the Apollo 11 mission that illustrated some of these aspects.

Bobby was absent today.

We reviewed the different phases in the evolution of average stars (like our Sun) and stars that are much more massive, say approximately thirty times the mass of the Sun. As in previous classes, we noted that average stars 'burn' for billions of years, go through the red giant phase followed by the (misnomer) planetary nebula phase, and eventually leave behind a glowing ember we call a white dwarf. Much more massive stars burn furiously and deplete their fuel in a matter of millions of years, explode in spectacular supernovae events, and leave behind black holes.

Having covered the Solar System fairly thoroughly, I thought it would be good to move on to other topics. Today we talked about the fact that all the elements we know are formed in fusion processes within stars. The first generation of stars that appeared shortly after the Big Bang (that occurred nearly 14 billion years ago) were mostly composed of hydrogen. They were hyper giant stars, and quickly burned hydrogen into helium (and a trace of other elements). When they had consumed their fuel, they exploded as supernovae, seeding nebulae with the elements that would then form the next generation of stars, such as our Sun. Today we covered the concepts of 'element', 'Big Bang', and 'supernova'. Gwendolyn remembered a video we had watched in the first semester on the scale of stars with respect to more familiar objects such as our Moon, so we watched that again.

We started class with a group activity involving one other teacher and one student, and then I wanted to sit down with Bobby and do some science. We talked a bit about black holes, but Bobby was so very eager to play chess. I could tell it was going to be a tad difficult to get him to engage in science at that stage, so I thought chess might be an excellent focusing activity. It sure was! Bobby is an excellent chess player, one can really see his analytical skills come to the fore. Bobby remained very concentrated for more than twenty minutes in a row.

The Sun's - or a star similar to the Sun - life cycle involves birth in a nebula, fusion of the elements for billions of years, the red giant phase, followed by the planetary nebula phase, and the outcome of all this is a white dwarf remnant. For a star much more massive than the Sun, say, 50 times, the fusion phase lasts only millions of years, the star then self-destructs in a powerful supernova event, and a black hole is formed. Today we reviewed these life cycles, and some of the associated vocabulary, such as the origin of the word 'massive' used both to describe a star much 'heavier' than the Sun, or the gargantuan black holes in the centers of galaxies (as in 'supermassive').

To kick off our nutrition unit, Stephen learned about additives, preservatives and artificial colors. We watched a video detailing a science experiment using McDonald's foods and "fresh made" hamburgers and fries. Stephen was shocked. Then we reviewed what was covered today before the end of class.