We finished the documentary on asteroids, and discussed the implications of space rocks slamming into Earth. Even if humans are not directly struck by an asteroid impact, one complication would be the enormous dust cloud that would engulf the Earth for possibly years after. This would seriously alter the climate, and have drastic consequences for farming, for example. The closest we've experienced was the Krakatoa eruption in 1883, when the year after the event, the global temperature fell by over 1 degree Celsius. It took almost a decade for the planet to recover. We then started summarizing this course, and went back to first principles, i.e. the scientific method. To conduct scientific experiments, the scientific method must be fully understood, otherwise the results and conclusions are meaningless. In addition, other methodologies, such as following up on references, are needed to ensure a solid, scientific foundation. Jared is very strong on the scientific method, and he remembers it from a 5th grade science fair experiment. It is very pleasing to see how he has retained that knowledge, and I have no doubt that in a real-world situation he would know how to apply it.

When we started class, Jared was browsing through images (artistic reproductions) of accretion disks being distorted by the strong gravitational fields of black holes (this is due to light-bending, not the actual distortion of the disks). So I thought to introduce him to the topic of 'gravitational lensing' and the Einstein Cross. This is a phenomenon whereby a massive object, e.g. a galaxy, sits between us and a distant quasar, and its gravitational field bends the light emanating from the quasar. More proof that Einstein was on the right track with his Theory of General Relativity! Then, to continue with catastrophes that may befall Earth (following on from Gamma-Ray Bursts yesterday) we watched a National Geographic documentary on the great scientist Eugene Shoemaker, and his growing understanding and lifelong commitment to studying impacts on Earth caused by asteroids, and the threat they pose to life on Earth. As always when we watch a documentary, we paused regularly to address scientific issues presented.

One topic that we hadn't yet covered that I really wanted Jared to learn about is Gamma-Ray Bursts. These are the most energetic events in the Universe (after the Big Bang) and remained a mystery until the 1990s when NASA launched the Compton Gamma-Ray Observatory with the intent purpose of investigating these intense, brief, explosive events. Today, the commonly held theories regarding the origin of these bursts is that they are the birth cries of black holes, either via the collapse of a very massive star (known as a 'hypernova') or via the coalescence of two neutron stars. This latter has implications for the study of elusive gravitational waves.

We continued discussing how the Sun's activity is almost wholly driven by magnetism at its surface. Coronal mass ejections and solar flares expel large numbers of particles at high speeds into space. If the Earth is in the path of one of these events, the interaction between the particles and the Earth's magnetic field manifests itself as aurorae, or Northern Lights. This phenomenon is mostly visible at high Earth latitudes, so the Southern hemisphere experiences them, too. The only caveat is that there are hardly any inhabited areas at latitudes higher than 60 in the southern hemisphere, apart from Antarctica. Hence we mostly refer to the 'Northern Lights'. The various colors observed in the aurorae are attributed to different elements (green is oxygen, red is nitrogen, etc).

The crucial element to any planetary system, including our own, is the star at its center. In our case, it is the Sun. It is important to understand how the Sun works, so that we can in turn understand the formation and evolution of the Solar System. By understanding our own Sun and planets better, we can then apply this knowledge to other stars and planetary systems. The Sun is a complex entity, with several layers ranging from the core at its center where the major fusion processes occur, through the radiative and convective zones, and finishing with the photosphere (the layer that we see), the chromosphere, and the spectacular and incredibly hot corona. Most of the Sun's activity can be attributed to magnetism. Jared was very attentive in class today, and again demonstrated such curiosity and asked such hard questions ... They were fun to answer!

Today we completed the section on exoplanets by watching the final minutes of yesterday's documentary. Jared - as always! - had excellent questions, specifically on orbits and spacecraft (in relation to the Kepler mission that has discovered some 4000+ exoplanets). So I took the opportunity to discuss a little bit more on the physics of electromagnetic radiation, and why certain detectors (for X-rays and gamma-rays) need to be placed in space, and why some observatories (e.g. infrared) are located in Antarctica. We also re-visited particle physics, so we could include a segment on neutrinos (elusive, almost mass-less particles that are a direct consequence of nuclear fusion e.g. in the Sun), and why neutrino detectors need to be placed deep in disused mines, for example. The groundwork is now in place to start on the Sun tomorrow.

Seeing as Jared had expressed such a strong interest in exoplanets throughout our course, and he had worked so hard on his assignment, we're wrapping up the section on exoplanets with a PBS Nova documentary that came out in 2014. As always, we pause at regular intervals, so that we can discuss the numerous points and questions that Jared brings up. We also discussed again how the orbital period of a planet around a parent star is directly related to its distance from the star (the closer in it is, the faster it will orbit the star) and that its distance is the only variable (once the mass of the parent star is known). One gets to this simply by equating the gravitational force between two objects (Newton's laws of gravitation) with the force an orbiting object experiences due to centripetal acceleration.

Today we reviewed the Assignment that Jared prepared over the holidays on the Solar System. His assignment is in PowerPoint format. Jared did an excellent job of organizing all the information we had gone over before the break into very neat slides. For each slide, he managed to insert one to two pieces of new information, i.e. stuff that we had not covered in class. His initiative in this respect was amazing! Jared also mentioned that he would like to continue working on the presentation in the days to come, and I thought it was an excellent idea. We concluded class by reviewing the theory of circular orbits, and calculated Earth's orbital period based on the equations. We will continue with various aspects of orbital mechanics in the next couple of classes.

Jared was absent today.

We finished discussing exoplanets, and moved onto studying in more detail what are the prerequisites for finding evolved life on other planets. A planet like the Earth needs to be in the 'habitable' zone, it needs a stable, older parent star, it has to have an atmosphere to protect it from coronal mass ejections and solar flares, the crust has to be thick enough to support oceans and landmasses, and so on. We concluded with discussing Drake's equation. Frank Drake, the de facto father of the SETI program, came up with an equation in the 1960's to estimate the number of technologically advanced civilizations in the Galaxy. Of course, many parameters require speculation, but it's a good mental exercise to picture the vastness of our Galaxy.