Weather, why atmospheres get thinner and colder as you go up, and the ideal gas law


I. The blue sky
-- tiny particles are shaken faster by the faster frequency of blue light, and the way to make light is to shake something fast, so a faster shake or a given amplitude sends out more (blue) light. -- this is called Rayleigh scattering -- your blue sky is being made by someone else's lovely red dawn or sunset
II. Rainbows
-- rainbows are caused by water droplets acting like a prism -- it is a refraction effect relating to the different wave speeds -- you see rainbow by looking away from the Sun
II. Planetary escape speeds
-- calculate Jupiter's atmospheric escape speed relative to Earth -- 12 times larger radius, 5 times smaller density -- implies 6 times larger escape speed -- for comparison: escape speed from Sun from Jupiter's orbit, relative to the case of the Earth: 5.2 times farther, so about 42 km/s divided by the square root of 5.2, or 17 km/s
III. More atmospheres in the solar system
-- Jupiter: dark belts and bright zones, Great Red Spot (unknown composition) surface rotation rate: 5 x10^5 km in 10 hours (= 3.6 times 10^4 s) is about 14 km/s ! (if Earth were rotating that fast, it would exceed escape speed and fly apart! -- such fast rotation has huge atmospheric effects: Coriolis is huge -- get dark bands, bright zones, moving at different speeds -- slide show -- Neptune: similar to Jupiter, Great Dark Spot -- Io: lots of sulfur and sodium -- Titan: only moon with thick atmosphere, similar N2 content to Earth, some methane
IV. Atmospheric pressure
-- weight of atmosphere is not negligible: 15 pounds per square inch! -- force is everywhere: cancels out (but materials are under stress) -- spacesuit and deep-sea diver suit look similar: note they perform the opposite function! -- high-flying jets are in the bottom of the stratosphere, about six times smaller air pressure. Planes are "pressurized". What happens when the hull is breached? -- The ideal gas law: PV = NkT P=pressure, V=volume, N=number of gas particles, k=a constant, T = temperature. Is this what determines P? Usually no-- it determines N/V usually (P comes from the weight of air above you, T comes from heating and cooling mechanisms, generally radiative, including greenhouse gases (that's why mountaintops are cold).