The Nebular Theory, Matter, and Light Matter – atoms and molecules Kinetic and potential energy Electromagnetic spectrum Spectroscopy Terrestrial, Jovian, and dwarf planets Nebular theory Goal du jour Understand more about matter, and how we use light to study the Universe.

The basics of matter Atoms The atomic nucleus Electrons Building blocks of matter. Atoms consist of a nucleus, and a surrounding cloud of electrons. The atomic nucleus Protons—massive, + charge Neutrons—massive, no charge Electrons Low mass, - charge # of electrons = # of protons

The basics of matter Elemental notation: He Isotopes Ions 4 2 1H = 1 proton (and 1 electron) 2H = 1 proton, 1 neutron (and 1 electron) 4He = 2 protons, 2 neutrons (and 2 electrons) Isotopes The same element (proton #), but different masses (i.e., different numbers of neutrons). Ex: He Ions Atoms temporarily stripped of one or more electrons. 3 2

The basics of matter Molecules are atoms that have been bound together by mutual attraction. Simple compounds O2, N2 Complex compounds CO2, H2O, C12H22O11 (sucrose), “DNA” Organic compounds Contain C-H bonds

Phases of matter Solid Liquid Gas Phases Freezing→ Sublimation→ (Plasma) Solid Freezing→ ←Melting Sublimation→ ←Deposition Evaporation→ ←Condensation Liquid Gas

Types of energy Kinetic Energy Energy exhibited by motions: speed, vibrations, rotations. Potential Energy Stored energy: at the top of a hill, a compressed spring, E=mc2 Radiative Energy Energy stored in photons, technically in each photon’s magnetic and electric fields, hence “electromagnetism.” Temperature A measure of how much kinetic energy is in a sample of molecules

Electromagnetic Radiation Photon A self-propagating packet of pure energy. c All photons all travel at the “speed of light”, the highest speed at which anything in the universe can travel. Frequency Higher energy photons have a higher frequency. Wavelength Higher energy photons have smaller wavelengths. Types of electromagnetic radiation radio→ microwave → infrared → ROYGBIV → ultraviolet → x-rays → Gamma rays

Spectra Spectrum A graphical display of the different kinds of photons in a beam of radiation. It might be portrayed as a line-graph, or (if visible light) as a multicolored display. This kind of smoothly varying, peaking spectrum is called a continuum spectrum. Continuum spectra are produced by opaque, glowing objects.

Continuum spectra The wavelength peak of a spectrum is affected by the glowing object’s temperature. Very hot objects glow blue. →We can take the temperature of objects by looking at them!

Electrons in atoms To understand the other kinds of spectra, we must first understand how electrons in atoms interact with photons. Electrons can jump from one level to another in atoms. An electron dropping towards the atom releases energy in the form of a photon. An electron must absorb a photon in order to jump to a larger orbit. Every different kind of element has a different set of electron orbit sizes. This will be useful.

Types of spectra Continuum spectrum Emission spectrum An opaque object will produce a continuum spectrum. Emission spectrum A transparent gas cloud, excited by some energy source, will produce an emission spectrum. Absorption spectrum A continuum source, with a transparent gas cloud in front it, will produce an absorption spectrum. Chemical analysis Since every atom has its unique set of electron orbits, each atom has a characteristic spectrum. →We can learn about the composition of gas clouds, or planets, or stars in space by looking at them!

Four classes of solar system objects Terrestrial planets Jovian planets Dwarf planets Moons of the Jovian planets (We’ll talk about them all in detail…later…)

Solar System models A good formation model should explain all these things. →See details of the Nebular Theory, p89. → Pay particular attention to origin of two types of planets.

Appendix: How gas discharge tubes work Gas normally does not conduct electricity 1)High voltage applied across gas drives electrons across the gap. 2)Electrons ram into the gas atoms in the tube, exciting the bound electrons (i.e., gives the electron energy). 3)The bound electron settles back to its ground level, releasing the stored energy as a photon. 3)Repeat