We get a planetary view of the atom

Nucleus 1/10,000 atoms diameter

99.9% of atoms mass is in the nucleus

BUT.....!!!

An orbiting electron must be accelerating…..WHY???Changing direction

So, it must radiate energy….WHY?Accelerating charges

cause EM radiation

KE & Momentum should be lost due to E-M radiation. Electron should spiral inward to nucleus

n=1 (Ground State)

n=3 (2nd excited state)

n=2 (1st excited state)

n=4n=5

n=3262 52 42

Larger Jump = More Energy = Bluer Wavelength

n=6

n=1 (Ground State)

n=3 (2nd excited state)

n=2 (1st excited state)

n=4n=5

Photons of all other energies (wavelengths) are ignored and pass on by unabsorbed.

n=2326 25 24n=6

Hydrogen

Helium

Oxygen

Neon

Iron

Nebula NGC 2363Nebula NGC 2363 This nebula is a glowing This nebula is a glowing

gas cloud about gas cloud about 10,000,000 LY from Earth.10,000,000 LY from Earth.

The hot stars in the Nebula The hot stars in the Nebula emit high energy photons emit high energy photons that are absorbed by the that are absorbed by the gas.gas.

The heated gases produce The heated gases produce an emission spectrum and an emission spectrum and the particular wavelength the particular wavelength of the red light of the of the red light of the nebula is 656nm. The nebula is 656nm. The exact wavelength of exact wavelength of Hydrogen.Hydrogen.

The Suns Absorption Spectrum

The Suns Absorption Spectrum from 420 – 430 nm. (TOP)The emission spectrum of Iron (Bottom)

In the late 1800’s astronomers were trying In the late 1800’s astronomers were trying to organize and make sense of all the data to organize and make sense of all the data they were collecting. they were collecting.

At the time, spectra studies were the most At the time, spectra studies were the most reliable, but there is a huge diversity of reliable, but there is a huge diversity of stellar spectra.stellar spectra.

In 1870’s stars were classified into various In 1870’s stars were classified into various letters based upon their spectral patterns.letters based upon their spectral patterns.

Hydrogen Balmer Lines StrongestHydrogen Balmer Lines Strongest

Stars containing heavier metals such as Stars containing heavier metals such as Calcium and Iron Calcium and Iron (Including the Sun, a G2 star)(Including the Sun, a G2 star)

Stars containing Titanium OxideStars containing Titanium Oxide

Hydrogen Balmer Lines Very Weak due to Hydrogen Balmer Lines Very Weak due to extreme tempsextreme temps

Hydrogen Balmer Lines fading out and trace Hydrogen Balmer Lines fading out and trace amounts of heavier elements starting to appearamounts of heavier elements starting to appear

In short, the In short, the OBAFGKM system OBAFGKM system allows us toallows us to

Identify the surface Identify the surface temperature of the temperature of the starsstars

Chemical composition Chemical composition of the starsof the stars

Where 4πR2 = area of a sphere

max ( ).

( )m eters

x

T K elv in

2 9 10 3

So we can determine the distances and characteristics of StarsWe need a betterbetter classification scheme