In this section of the class, we'll be talking about the fundamental principles of matter and radiation that underlie the subject of astronomy. We'll talk about the structure of matter, the distinction between atoms, molecules, ions, and isotopes, and also how atoms are put together from tiny compact nuclei and large clouds of negatively charged electrons. We'll also talk about new information on the substructure of matter, indicating the protons and neutrons are not fundamental particles, but made of quarks, and hinting at an even deeper level of structure which may be interpretable in String theory. We'll look at radiation as well and the equivalence of matter and radiation, in terms of Einstein's famous equation, E equals MC squared. We'll consider the different forms of energy, which in the universe are interchangeable. The most profound form of energy that we'll deal with in this class is light and other types of electromagnetic radiation. They are all unified in terms of being electromagnetic waves traveling at the same speed, 300,000 kilometers per second in a vacuum. Radiation is fundamental to how we understand the universe. Astronomers not only collect radiation but they disperse it by wavelength into spectrum, and spectroscopy is a key tool of astronomy. So we'll look at what can be learned from spectroscopy, which enables us to remotely diagnose the composition, temperature, and even density of remote astronomical objects such as stars, compact remnants of stars, and even entire galaxies. Then we'll look at matter and in particular, the theory of gravity that underlies all of the structure of the universe, from planets to stars to galaxies. The theory of gravity from Isaac Newton applies in almost every location in the universe. But in the early 20th century, Einstein developed a new concept of gravity that applies more accurately in regions where the gravity is strong. This is general relativity, and we need it to understand not only black holes and neutron stars, but also the entire universe and its evolution.