We reviewed last week's lessons, seeing as Jared was absent two days, and I could see he was not feeling well on Tuesday. He remembered a lot, despite everything! It was a very good lesson - once I saw Jared was remembering the lessons, I started to quiz him, as I used to do, and he did great. Then we started on the concept of the search for 'life' in the Universe, always stressing that it need not be like life here on Earth. We discussed the challenges for planets to host life, such as the extent of the 'habitable zone' and the presence of an atmosphere and a magnetic field, both of which shield the planet (as in our Earth) from harmful radiation from space. Jared was very attentive throughout the class, and again asked many interesting questions. It's good to have Jared back!

Jared was absent today.

Jared was absent today.

Today we finally started on a subject that has fascinated Jared since we started this course: planets outside our own Solar System, or exoplanets. We discussed why it's been so difficult even starting to find them - the first one was not discovered until 1995. This has to do with the fact that the light from the parent star completely drowns the light from the planets, and rather sophisticated techniques and instruments needed to be developed. Today, there are nearly 5000 known exoplanets, most of them discovered thanks to the Kepler mission.

Seeing as I hadn't seen Jared since December 10, we spent some time catching up - we discussed the National Geographic DVDs on the Universe I had lent him, and he told me what had interested him most. Being the season, we also discussed the winter solstice (December 21) and what that implies for the northern and southern hemispheres, and conversely how the summer solstice (June 21) affects the hemispheres. We also discussed the Tropics of Cancer and Capricorn (at +23 and -23 degrees latitude respectively) and how that is the extent on the globe at which you will find the Sun directly overhead on the summer and winter solstices respectively. Perihelion (Earth's closest approach to the Sun) also occurs at this time of the year, around January 3 or 4, and we talked about why this happens (the Earth's orbit is not perfectly circular around the Sun). It was a great pleasure to find Jared as attentive and curious as when I left over a month ago - a real joy to teach!

In summary, we reviewed the main characteristics of the objects found in the Solar System. We finished exploring the outer Solar System planets, Neptune and Uranus, and talked about the asteroids in the asteroid belt and dwarf planets in the Kuiper Belt. We also prepared the groundwork for Jared's assignment for the holidays.

I had barely walked into Jared's room when he excitedly asked me if I had recently checked the website 'Astronomy Picture of the Day' - Jared was enchanted with the video that had just been posted, and wanted to share it with me. It was a 3-minute video on the exploration of other worlds, voiced over by Carl Sagan. Following that, we discussed the pros and cons of space exploration/travel - Jared was very curious about the Challenger disaster in 1986, and its consequences. He had some very relevant questions regarding the origins of spaceflight, and so we discussed Robert Goddard and Wernher von Braun and the early history of rocketry. We covered some basics of orbital dynamics, a topic we will concentrate on next semester, also in the context of planetary motion. Jared appears to be fascinated by the concept of 'physics' (e.g. Coriolis forces, spacecraft orbits, etc) and shared some stories with me of how he recently had to explain certain physical concepts to some of his friends. We concluded the section on the scale of the Solar System, by scaling the planets to the Sun if it had a diameter of 22 inches (the diameter of a tire/wheel on one of the Renntech cars). The rocky planets would then all be under a half inch in diameter, while the gas giants would only be a few inches across.

We continued today with exploring the planets in our Solar System. We discussed how they are divided into four inner rocky planets all scrunched together and four outer gas giants spaced further apart. Jared appears to have grasped the concept of the formation of the Solar System extremely well (a collapsing cloud) and by himself associated this phenomenon with the larger phenomenon of galaxy formation. He again had such intuitive questions regarding the planets and their properties, and as always remained very attentive in class. For part of today's second period we watched a National Geographic documentary on the planets and, as before when we've watched a documentary (once on the Big Bang and once on relativity), we didn't get through it because Jared had so many relevant questions! It's a real pleasure to witness his curiosity. Jared himself assigned his homework for the weekend! - and has already thought of what he could work on while I'm away.

Even though the objects in the Solar System are those closest to us in the Universe, the distances to the farthest ones are nevertheless inconceivable. We started class by contemplating 'The Pale Blue Dot', the first-ever image taken from beyond Moon's orbit of Earth from the Voyager 1 spacecraft. At the time, Voyager 1 was at Pluto's orbit. After finding out the distances to the eight planets plus Pluto, we then re-scaled those distances to correspond to the same scale as if the school were the Sun and Jared's home were Pluto. If Jared's house is at 10km from the school, then the four inner rocky planets all lie within 400 meters (approximately 400 yards) from the school, and the gas giants fill out the rest of the space. No wonder when Voyager 1 looked back at the Earth it was a barely visible dot!

Today we started covering the Solar System. We looked at the Solar System as a whole, and discussed the main objects - the Sun, the planets, their moons, dwarf planets, comets, asteroids. We calculated what fraction of the Solar System's mass resides in the Sun, and concluded that it is over 99%, making the Sun the overwhelmingly dominant object in the Solar System. As always, I am very pleased with how curious Jared is, and how full of - totally relevant - questions he is. Jared remained attentive throughout the class, even though it was a double session.