Week 7, clip 4

Timepoint:  00:47.8

1) Astronomers use a different short-hand terminology for describing ionization of atoms in space.  Here are a few examples. 

Neutral atomic hydrogen:  astronomers use HI (chemists, for example, use either H^0 or just H)
Ionized atomic hydrogen:  astronomers use HII (compared to H^+ or H^+1)
Triply ionized atomic oxygen:  astronomers use OIV (compared to O^+3)

Timepoint:  06:36.9

2) When astronomers use the term 'dust', it has a different meaning than the fuzz swept up from under couches or off high shelves.  Dust in astronomy typically refers to anything above the size of an atomic element.  Thus, molecular hydrogen (H_2), carbon monoxide (CO) and any other molecules fall into the 'dust' category.  Gas typically refers to atomic elements in space; anything from atomic hydrogen to atomic uranium.

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