The Nebular Theory, Matter, and Light

1. Terrestrial, Jovian, and dwarf planets2. Nebular theory 3. Matter – atoms and molecules4. Kinetic and potential energy5. Electromagnetic spectrum6. Spectroscopy

Goal du jour

Understand more about matter, and how we use light to study the Universe.

Four classes of solar system objects

Terrestrial planets– Close to Sun– Small– Rocky– Few (if any) moons

Jovian planets– Far from Sun– Giant– Gaseous– Many moons

Dwarf planets– Rock and ice – Rock and metal– Often cometary– Tiny

Jovian moons– Rock and ice– Small– Very exciting

Solar System models

A good formation model should explain all these things.→See details of the Nebular Theory, p79.

→ Pay particular attention to origin of two types of planets.

The basics of matterAtoms

Often considered the building blocks of matter, but atoms have internal structure.

Atoms consist of a nucleus, and a surrounding cloud of electrons.

The atomic nucleusProtons—massive, + charge

Neutrons—massive, no charge

ElectronsLow mass, - charge

# of electrons = # of protons

The basics of matter

1H = 1 proton (and 1 electron)2H = 1 proton, 1 neutron (and 1 electron)4He = 2 protons, 2 neutrons (and 2 electrons)

IsotopesThe same element (proton #), but different masses (i.e., different numbers of neutrons).

Ex: He

Ions Atoms temporarily stripped of one or more electrons.

AntimatterMuch like normal matter, but with key characteristics being opposite the state we are familiar with: antiprotons, antielectrons (positrons, etc).

.

Elemental notation: He42

32

The basics of matterMolecules are atoms that have been bound together by mutual attraction.

Simple compoundsO2, N2

Complex compounds CO2, H2O, C12H22O11 (sucrose), “DNA”

Organic compoundsContain carbon (C) -- or --Contain C-H bonds

Phases of matter

PhasesSolid

Liquid

Gas

(Plasma)

Solid

Liquid Gas

Free

zing

→←

Mel

ting

Evaporation→

←Condensation

Sublimation→

←Deposition

Types of energy

Kinetic EnergyEnergy exhibited by motions: speed, vibrations, rotations.

Potential EnergyStored energy: at the top of a hill, a compressed spring, E=mc2

Radiative EnergyEnergy stored in photons, technically in each photons magnetic and electric fields, hence “electromagnetism.”

TemperatureA measure of how much kinetic energy is in a sample of molecules

Electromagnetic Radiation

PhotonA self-propagating packet of pure energy.

cAll photons all travel at the “speed of light”, the highest speed at which anything in the universe can travel.

FrequencyHigher energy photons have a higher frequency.

WavelengthHigher energy photons have smaller wavelengths.

Types of electromagnetic radiationradio→ microwave → infrared → ROYGBIV → ultraviolet → x-rays → Gamma rays

Spectra

SpectrumA 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 spectraThe 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 spectrumAn opaque object will produce a continuum spectrum.

Emission spectrumA transparent gas cloud, excited by some energy source, will produce an emission spectrum.

Absorption spectrumA continuum source, with a transparent gas cloud in front it, will produce an absorption spectrum.

Chemical analysisSince 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!

Gas discharge tubes

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