Atomic Physics & Particle Physics
Atoms and the minute particles from which they are made strongly influence the nature of many phenomena that play out their roles on astronomical scales. The fields of atomic physics and particle physics provide many valuable insights into the life cycles of stars, the forms of spaceborne radiation, and the way we can use spectra to study distant objects.
The discipline of atomic physics concerns itself with atoms, the particles from which atoms are made, and the various energy states that atoms can take on. The tiny, dense nucleus of an atom is made up of protons and neutrons. Clouds of electrons, less than a thousandth the size of the nucleons, buzz around the nucleus in a complex array of energy states.
Particle physics delves into scales even smaller than the atom as it sheds light on the worlds of subatomic physics. When atoms are torn apart, usually in the presence of large amounts of energy, subatomic particles come out to play. Some are familiar, such as protons, neutrons, and electrons; others are more exotic, bearing strange names like muon, neutrino, baryon, meson, and the elusive quark. Plasmas, such as the "soup" of electrons and protons that makes up the solar wind, and many of the most dangerous forms of radiation, such as cosmic rays, are collections of subatomic particles.
The "laws" of physics at atomic and subatomic scales are so different from those we observe in our "normal" daily experiences that physicists had to invent a whole new field to describe them. The discipline of quantum mechanics predicts the strange behaviors found in the worlds of the very small. In the realms of quantum physics, the distinctions between particles and waves disappear, we lose our ability to define the locations of objects in favor of probabilistic descriptions of where particles are likely to be, and the mere act of observing a phenomenon can fundamentally alter its behavior.