Spectral lines

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From "Astronomy! A Brief Edition," J. B. Kaler, Addison-Wesley, 1997.

Slide 11

Kirchhoff’s Laws Cont…

Excited electrons, don’t stay excited forever.

Drop back down to their ground floors.

Only light of the precise energy difference between floors is given off.

This light goes off in all directions.

From a second detector, we see these specific energy wavelengths: an emission spectrum.

Slide 12

Continuum, Absorption, Emission

Slide 13

Spectral Lines

Heat low density gas and it will glow.

Pass the light through a slit to get a narrow source.

Pass light from the slit through a prism.

Get multiple images of the slit, each at a different wavelength.

These “lines” are the element’s “finger print”.

Spectrometer

Slide 14

Emission Lines

Every element has a DIFFERENT finger print.

Slide 15

Multiple elements

Gases, stars, planets made up of MANY elements have spectra which include ALL of the component spectral lines.

It’s the scientist’s job to figure out which lines belong to which element.

Slide 16

Different stars, different spectra

Different stars have different types of spectra.

Different types of spectra mean different stars are made of different elements.

Hot

Cool

Stellar Spectra

Annals of the Harvard College Observatory, vol. 23, 1901.

Slide 17

To Sum Up…

EVERY element has a SPECIAL set of lines.

Atom’s fingerprint.

Observe the lines and you identify the component elements.

Identify:

Absorption spectrum

Emission emission

Learn about the environment of the element

Slide 18

Concept Test

The sunlight we see is thermal radiation caused by the extreme heat of the sun’s surface. However, the very top thin layer of the sun’s surface is relatively cooler than the part below it. What type of spectrum would you expect to see from the sun?

A continuous spectrum.

A continuous spectrum plus a second, slightly redder continuous spectrum.

A continuous spectrum plus a second slightly bluer continuous spectrum.

A continuous spectrum plus an emission spectrum.

A continuous spectrum plus an absorption spectrum.

Slide 19

The Sun