Light is a wave or electric and magnetic energy The speed of light is 186,000 mi/s = 300,000 km/s

Energy = hf = hc/ f = frequency h = Planck's constant = wavelength Highest energy (E) Highest frequency (f) Shortest Wavelength ( ) Lowest energy Lowest frequency Longest Wavelength c = f x c = speed of light

Atoms are comprised of a nucleus and electrons (in orbits -> would appear as a swarm or cloud) protons = positive charge; neutrons = no charge; electrons = negative charge

The nucleus is extremely tiny; atoms are empty space! This atom is blown up a trillion times = = 1,000,000,000,000 = 4.5 football fields = 450 yards = 1350 feet = ¼ mile

Atoms are defined by atomic number = number of protons hydrogen = 1; helium = 2; carbon = 6 The number of electrons is equal to the number of protons. A given atom does not always have the same number of neutrons (or mass). These different “flavors” of a given atoms are called isotopes.

The electron(s) are allowed only in permitted orbits; unlike planets in a solar system. The locations (sizes), and therefore energies, of these orbits are unique to each atom

The hydrogen atom Energy is measured in eV, or electron volts Light (photon) is electromagnetic energy Since only permitted electron orbits (energies), there are only permitted photon energies that interact with the atom. The photon energy equals the energy difference of the electron orbits (not shown) (true colors) Energy = 12.8 – 10.2 = 2.6 eV

Just to drive the point home… Note in right most panel that the electron slipped back down. This is the process of emission. absorption process emission process

A solid object emits a continuous spectrum A “perfect” object emits a blackbody continuous spectrum The shape and total energy depend upon only one quantity = temperature LAW 1

Blackbody Radiation max = 3,000,000 T nanometer E total = constant x T 4 J/s/m 2 E total = area under BB curve T = absolute temperature Absolute temperature measures the internal kinetic energy of an object. This is the energy from all the motions of the atoms.

LAW 2 A heated gas emits a emission spectrum The spectral lines depend upon the type of atoms.

Each atom has its unique spectral “fingerprint”

LAW 3 A “cool” gas in front of a hot source yields an absorption spectrum The spectral lines depend upon the type of atoms.

Stars have absorption spectra.

Stellar spectrum showing hydrogen absorption.