We watched the last part of the documentary on the Big Bang that concentrated on the Higgs field and boson, responsible for the mass of things in the Universe. We discussed the Large Hadron Collider, a particle accelerator 16-miles underground, straddling the French and Swiss border, and the instruments built to detect the Higgs. The documentary concentrated on the first second of the Universe, and Jared began asking very tough questions on the concept of time..! (We will start with stars tomorrow, Jared appears so fascinated by the Big Bang and its consequences, I wanted to spend a bit more time on it.)

Jared has worked so hard these past few weeks, that for our review session for the Big Bang and large-scale structures in the Universe we watched a video on the first second of the Big Bang featuring two well-known and much-respected science communicators of today, astrophysicist Lawrence Krauss and physicist Michio Kaku. We ran out of time, for again Jared asked all the right questions, so I paused to discuss them with him. Monday we will start with a new topic, stars!

We concluded the topic of large-scale structures in the Universe by discussing the Local Group of galaxies, of which the Milky Way is a member, and continued by exploring clusters of galaxies. The largest structures in the Universe are clusters of clusters of galaxies, known as 'superclusters'. A galaxy redshift survey conducted over many years has mapped the location and extent of superclusters out to about 2 billion light years. This map shows the presence of 'filaments' and 'voids', and informs us on the distribution of matter in the Universe at large, and helps to prove that the Big Bang was not perfectly symmetrical.

In today's class we reviewed the structure of the Milky Way, emphasizing the fact that a supermassive black hole resides at the center. The mass of the black hole is about two-and-a-half-million times the mass of our Sun, yet fits in a volume smaller than one tenth the orbit of the Earth around the Sun. That's dense! It transpires that all galaxies in the Universe contain supermassive black holes at their cores. Very distant galaxies, known as 'quasars' (from 'quasi-stellar source') were discovered in the 1960s, and radio observations showed them to power radio jets emanating perpendicularly from their core at nearly the speed of light.

We started class by reviewing the three main types of galaxies (elliptical, spiral, barred spirals; Jared's homework over the weekend), highlighting the fact that ellipticals are older than the spirals, and were probably formed through mergers of two or more galaxies. We then proceeded to discuss the structure of the Milky Way - that it's a barred spiral and consists of a central bulge and nucleus from which the bar and then the spiral arms emanate, and that the Solar System is situated in one of the outer spirals, approximately 8 kpc from the center. We reviewed how - through observations at different wavelengths we came to understand the structure of the Milky Way, and we concluded the session talking about the supermassive black hole sitting at the center.

We reviewed the scale of things in the Universe, starting with Earth, working our way through the other planets in the Solar System, going up in scale through the different types of stars, and ending up in the Hubble Deep Field where there are tens of thousands of galaxies, some nearly 13 billion light years away. This was to set the field for studying the basic 'building blocks' of the Universe, i.e. galaxies. We looked at the 'Hubble Tuning Fork' classification of galaxies, and discussed where the Milky Way fits into this classification.

We started class by discussing eclipses, since Jared had seen the lunar eclipse this morning. We discussed the difference between solar and lunar eclipses. We then returned to the Big Bang, and I explained to Jared the interaction between elementary particles (protons, neutrons, electrons, quarks, etc) and radiation, and why the early Universe was opaque. We talked about particle accelerators and cloud chambers, and how through high speed collisions we can understand better the fundamental building blocks of matter. Using what we know today, we can work backwards and infer (with sophisticated mathematical tools) what physical processes dominated in the first 380,000 years of the Universe.

We covered one of the most important milestones in the history of cosmology, the discovery of the microwave background by Penzias and Wilson (they later won the Nobel Prize for this achievement). This confirmed the theory of the Big Bang as the birth of our Universe. We then discussed the first few seconds after the Big Bang and the production of matter and antimatter in slightly unequal amounts which resulted in the formation of the first stars and then galaxies. We then covered the fact that until 380,000 years after the Big Bang radiation and matter were coupled, and hence we cannot directly observe anything before that time, so we have to build on our current knowledge of physics to infer the physical processes that occurred.

We continued exploring the scale of the Universe. We started by discussing space flight, and how the farthest human beings have been is the far side of the Moon. We reviewed the light year, and looked at the distances between various Solar System objects. Jared realized that compared to the light year, the Solar System (from the Sun to Pluto) is really not that large in the big scale of things. We also talked about Voyager I and how it has recently left the heliosphere. This is all groundwork in anticipation of covering the size of the whole Universe, how far it has expanded since the Big Bang.

Jared and I have started exploring the scale of the Universe in preparation for a more full-depth study of the evolution of the Universe following the Big Bang. We discussed the fact that lightyears are in fact units of length (and not time), and we looked at the the size of the Milky Way in terms of lightyears. I also introduced Jared to the 'parsec', the basic unit of distance used in astronomy (outside of the Solar System), and showed how it relates to the lightyear.