Astronomy 1 (Physics 1513)
Lecture Notes
Wednesday, Oct 28, 1997

The Earth
(Interior, Atmosphere, Energy Balance, Tectonics)

Read Text Chapters (Chaisson and McMillan) #7 - The Earth (include Interludes)
More Precisely 7-1 (Atmospheric Scattering)
More Precisely 7-2 (Radioactive Dating)
More Precisely 8-1 (Trapping Atmosphere on Planets) 
Notes:
Homework Due Wednesday, Nov 4: 
(See also Assignment #6 on Acme)
Chapter 6 Probs #2, 9, 10
Chapter 7 Probs #2, 3, 4, 10
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Where we are in the course:
Done Chap 1-6 (Weeks 1-8)
To do Chap 7-15 (Weeks 8 - 13)
	approximately 1 chapter per class period (
	(two per week)
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LECTURE

(Outline - read Chapter 7 for details) 
Atmosphere
	How Planets Keep their atmospheres (New Physics)
	More Precisely 8-1 (Trapping Atmosphere on Planets)
		Thermal distribution of molecular speeds
			vaverage= (3kT/m)1/2
			H2 --> 6.2 km/s
			4He --> 4.4 km/s
			N2 --> 1.6 km/s
		Escape Velocity	
			vescape= 11.2 km/s
			rule of thumb to escape 
			6 * vaverage > vescape
		
	Earth's Atmosphere History 
		- 1st - Hydrogen, Helium (Remnant of Solar Nebula)
		- 2nd Volcanic - Carbon Dioxide, Sulphur Dioxide, Water Vapor
		- 3rd (3.5 billion ya) Oxygen/Nitrogen from life (algae)

	Height Profile 
		Temperature (figure 7.2)
			reversal defines 
				Troposphere (0-12 km)
				Stratosphere (12 - 45 km)
				Mesosphere (45 - 80 km)
				Ionosphere 100 km
		Pressure (Force/Area) 
			Sea level - 101,000 Pascals = 1 bar = 14.7 lb/in2
				= 760 mm Hg = 30 inch water
			Pascal = N/m2
			Change in pressure with height = 1 inch/1000 feet
			 
		Fraction of Atmosphere
			21% oxygen
			78% nitrogen
			0.03% Carbon Dioxide
			0.1-3% Water Vapor
	
	Radiation Balance (New Physics)
		Concept of Albedo (depending on wavelength)
		Concept of Greenhouse effect 
			(wavelength dependent transmission)
		Short Wave (Solar Radiation)
		Long Wave (Heat)

	Atmospheric Optics (New Physics)
		Blue Sky, Red Sunset 
			Rayleigh Scattering ~ 1/(wavelength)4
			When particles < 0.1 of wavelength (molecules)
		Ice Halos. sun Pillars and Rainbows
		Scintillation (Due variations of index of refraction)

	Circulation of the Atmosphere (Convection Cells) (New Physics)
		Coriolis effect (New Physics)
		Tropical, Temperate, and Arctic Cells
		Wind Directions

Interior of the Earth
	[concept of Pressure and Shear Waves - seismic waves] Figure 7.6
	Crust (Ocean versus Continent) Thickness and Composition
	Mantle Temperature and Convection
	Core
	Pressure and Temperature with Depth (Figure 7.7)

	Tectonics 
	(Mountains, Troughs and Mid-ocean rifts, Volcanoes and Hot Spots)
		Movement ~ cm/yr

	Age of the Earth 
		Nuclear Physics and Radioactive Decay (New Physics)
		(elements used)			Half-life
		40K --> 40Ar		 1.3 billion years
		238U --> 206Pb 		 4.5 billion 
		232Th --> 208Pb		14.0 billion
		87Rb --> 87Sr 		48.8 billion 
		
	Daughter Nucleii and aging

Magnetosphere
	Magnetic Dipole Field of the Earth (New Physics)
		Angle of magnetic dipole to Earth geometry
			North Magnetic Pole 76N 100W
			South Magnetic Pole 66S 139E
		magnetic field ~ 0.5 Gauss (0.00005 Tesla)
	Trapping of charged Particles in a magnetic field (New Physics)
		Van Allen Belts:
			Particles E=10-100 keV H+  (<10/cm3)
		Aurora (green 558nm oxygen lines) 
	Solar Winds and magnetosphere (protons and electrons)

Plate Tectonics
	Crust and Mantle circulation
	Plate collisions (movement ~ cm/year = 1000km/108yr)
		Mountains
		Subduction zones and Volcanoes
		Faults
	Mid-Ocean Ridges 
		Magnetization variation and age
	History of Crust Movement

Oceans
	Circulation
	Tides
		Physics of Tidal Effects (New Physics)
			Differential Tidal Force ~ M/r3
		Timing of Tides 
			Daily (52 minute delay of high tides)
			Phases of the Moon (neap and spring tides)
			(Tides due to the Sun = 1/2 those due to the Moon)
		Slowing of the Earth's Rotation (2 ms/century)
			Determined by coral growth daily rings and annual rings
			(Friction of water on the ocean bottoms)
		Moon recedes from Earth (4 cm/year)
		(Earth angular momentum decreases so to keep the 
		total momentum of the Earth-Moon system constant
		the orbital momentum of the Moon must increase -
		orbital momentum, L~r1/2 so the radius
		of the orbit must increase)
		[NOTE: L=mvr but Kepler's 3rd law says r3~P2
		and P = 2(pi)r/v. So v ~ r-1/2 and when
		all this is put together L~r1/2]
NEW PHYSICAL PRINCIPLES INTRODUCED IN THIS LECTURE
(We will see them again and again in talking about other planets)