by Dr. James D. Livingston

From absorption by the MOs
Blood is red and grass is green
From emission by the AOs
The red Citgo sign is seen

Copper's red 'cause d electrons
Preferentially get the blues
And absorption 'cross the band gaps
Gives the pigments gorgeous hues

Chromium makes em'ralds green
And gives rubies their deep red
Nitrogen makes diamonds yellow
Boron makes them blue instead

Although photons can be useful
And in commerce due their duty
They also please our senses
As they color nature's beauty

Skies of blue can span the spectrum
When the sun sets in the west
In such things and in the rainbow
We see physics at its best


Citgo sign in Boston. (Click image to enlarge.)
Image courtesy of Prof. Steven Pinker


The Physics of why gemstones are colored.


Rainbow in Montana. (Click image to enlarge.)
Image courtesy of Pat's Mauna Kea Star Tours.
The Physics of Rainbows.

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