The Spectrum

Page
4

An answer to an old question

From this work B&K understood what the Fraunhofer lines were

‘the vapour of table salt absorbs the same lines which it also emits. These lines are identical with solar Fraunhofer lines’.

So, there is a connection between emission and absorption!

And stars??

Warning! Science Content Follows!

Slide 31

Every element (and molecules too) emits a unique set of spectral lines

It’s like every chord on the piano has a unique set of pitches

But two questions come to mind:

Why does each element emit a unique set of spectral lines?

Why did it take so long for scientists to concertedly look for these lines?

Slide 32

Second Answer First

At the time of Newton’s death in 1727, only 14 of the 114 elements had been identified

Even by 1800, only 32 elements had been isolated

But by 1859, the time of Bunsen and Kirchhoff’s paper, known elements were so numerous that chemists were eager to qualify and quantify them

And, of course, Astronomers weren’t interested at all

Slide 33

Now, the First Answer

This interesting phenomenon, seemingly pertinent only to chemical identification, was one of the motivating forces for a major change in Physics in the 19th and 20th Centuries

“Clouds over Physics”

“Electromagnetic Catastrophe”

Slide 34

Faraday and Maxwell

It was known through the work of Michael Faraday and James Clark Maxwell that moving electrons radiate energy

This is a slightly more modern picture of an atom

Slide 35

But the (19th C) Problem is:

If an electron is continually buzzing around an atom, it is constantly giving off energy

If it is constantly giving off energy, its path would decay and the electron would spiral into the nucleus

The electron would emit the entire spectrum as it spins down, not discrete colors

And atoms and therefore matter everywhere would collapse

Slide 36

Max Planck’s Kludge

Planck suggested that electrons can travel only in specific paths or orbits about the nucleus

That way they would never lose all their energy and spiral in

He admitted that the atom probably wasn’t like this, but the math worked out as if it did

Slide 37

But Atoms Do Work This Way!

Slide 38

Orbits and Spectra