The Spectrum

Page
5

Every element’s atoms have a unique set of discrete energy levels (orbits)

As the electron drops from a higher to lower orbit it sheds a unique color of light

Small energy jumps: red light

Big energy jumps: violet light

The set of colors (a series) gives each atom its distinctiveness

AND, if a photon of just the right energy hits a cool, rarified gas, the gas absorbs that color

Fraunhofer lines!

Slide 39

Without going into great detail…

Planck contributed to a new science called Quantum Mechanics (term dates from 1927)

Quantum Mechanics was a sea change in the way scientists (and non-scientists) saw the cosmos

Newton’s idea of a deterministic universe was supplanted by a probabilistic universe

In other words, there is no absolute certainly (I think)

Slide 40

A Powerful Technique

Bunsen and Kirchhoff said something to the effect that, if Heidelberg was burning they could determine what is was made of

They then metaphorically looked at each other and realized they could tell what the Sun was made of*!

And they found it wasn’t burning in the “normal” sense

As an aside, contemporaries Herman von Helmholtz and Lord Kelvin postulated that the Sun shined from a release of gravitational energy

*Of course, others had this idea as well, but B & K are best know for it.

Slide 41

If we were to go to the sun, and to bring away some portions of it and analyze them in our laboratories, we could not examine them more accurately than we can by this new mode of spectrum analysis. —Warren De La Rue (1861)

Slide 42

Kirchhoff’s Laws

After further study Kirchhoff postulated three laws:

A rarified hot gas gives off emission spectra

A dense cool gas absorbs light at discrete colors (absorption spectra)

A dense hot gas emits a continuous spectrum

Slide 43

A New Science: Astrospectroscopy

Astronomers break the light from stars, nebulae, and supernovae into its constituent colors

Using Kirchhoff’s Laws they can tell what a hugely distant object is made of, whether it is hot, cold, rarified or dense

Slide 44

Pioneers in Stellar Spectroscopy

Giovanni Battista Donati (1826-1873)

Father Pietro Angelo Secchi (1818-1878)

Lewis Morris Rutherfurd (1816-1892)

Slide 45

Comparing stellar spectra

Donati (1863)