AST201H5 Lecture Notes - Lecture 5: Chemical Element, Mass Number, Atomic Number
Document Summary
Ultraviolet - about 200 nm x rays - about 1 nm. Before 1950s, astronomy used only visible light. Since 1950, astronomy has had the technology to use all forms of radiation. Light is both a wave and a photon at the same time. Brightness of light number of light photons /s. Light is so important because it brings us info about distant matter. Most fundamental form of matter = atoms. About 100 different kinds of atoms = different chemical elements. To connect light, matter we need to understand the structure of an atom. Atoms have 3 basic components: proton (+, neutron (n^0, electron (-) The electric force dominates inside the atom, and gravity is negligible. Electron"s mass is negligible compared to the proton or neutrons mass. Protons and neutrons are confined to a tiny nucleus, about 10^-15m across, nucleus has all the atom"s mass, nucleus has a + electric charge.
