LECTURE: Nov 4, 1998
Moon and Mercury Temperatures
Transits of Mercury and Venus
Venus Properties

Chapter 8
Review Question #14
Problems 7, 9
Chapter 9
Review Question #6, 9
Problems 1, 10
Project with ECU
- Determine where Venus is with respect to the Sun
(Elongation) on the following Dates:
Nov 1, 1998
Dec 1, 1998
Jan 1, 1999
Feb 1, 1999
Mar 1, 1999
	Describe where to look for Venus in those coming
months and what it will look like (how bright and where).

Previous Lecture (Moon and Mercury)

Temperatures of the Moon and Mercury:
	Mercury: No axial tilt - Slow Rotation (58.7 days) - Cold poles - Hot Equator 
		No Atmosphere of significance
		88 - 700 K
	Moon: slow rotation (27.3 days) - small axial tilt - no atmosphere
		103 - 383 K (120 C)
	Earth: An atmosphere well mixed to equalize temperatures
		~ 280 K

Origin of the Moon Impact Theory vs Daughter, Capture, Coelescence
History of Moon Surface Impacting Sequence
Mercury's Surface and Caloris Basin
	Large core, thin crust, concentrate shock waves
	yield "weird" terrain

Transits of Mercury and Venus:
Mercury		 9 May 1970 
		10 Nov 1973
		13 Nov 1986
		15 Nov 1999 (6pm local time - sun has set - graze)	
		May 07 2003      07:52 UT  (4:52 ADT)          
           	Nov 08 2006      21:41 UT  (18:41 AST)          
		
Venus 	(at its nodes in June and December - 
	5 synodic periods = 8 earth years - 2 days
	1761
	1769	James Cook sent to South Seas to observe this one 
		to determine the AU (The ship HMS Endevour)
		- before 1700, 1 AU was thought to be ~1200 R(Earth) 
		when actually was 23,455
	1874
	1882		
	2004 Jun 08     08:19 UT (5:19 ADT)        10.5' arc from center
        2012 Jun 06     01:28 UT (        9.2' arc from center

	8 June 2004 (3 am ADT)
	6 June 2012 (9 pm ADT)  Both times not visible in Eastern N.America


The region of the node of Venus' orbit. 
At inferior conjunction Venus is moving 1.6 deg/day in its orbit so 
	Venus is only in position for a transit for 2.6 days per year.
	(1 chance in 140 per Earth year)

Because the orbits of Venus and the Earth are nearly synchronous 
with a ratio of 8 to 5, the coincidence does not occur very often. 
But when it does then it occurs during two successive identical 
configurations, 8 years apart. (shift of 2 days but node region is 2.6 days wide)

Venus Physical Properties

Mass			0.82 Mass of Earth
Radius			0.95 R of Earth
Surface Gravity		0.91 g of Earth
Escape Velocity		10.4 km/s
Rotation Period
	Siderial	243 days retrograde (East to West)
	Synodic		116.7 days (shorter because rotation and 
				revolution are in opposite directions)	
				-Note: Synodic period relative to the 
				 Earth is 583.9 days = 5 x (116.7 days)
				The same face of Venus faces the Earth at 
				every inferior conjunction!!!

Mean Surface Temp = 730 K due to a large 'greenhouse effect'

Illustration of radiation balance for Venus - No Greenhouse Effect
		Solar Radiation Absorbed = Infrared Radiation Radiated into Space

	1.
		Radiation from the Sun: 1370 W/m2/(0.72)2
			F(Sun) = 2642 W/m2
		Area of Venus's Disk = (pi)R2
		Albedo: a = 0.79 = Fraction of sunlight reflected
		Fraction of Sunlight absorbed = 1 - albedo
		ISun = Absorbed Sunlight = (1-a) F(Sun)(pi)R2
	2.
		Infrared radiation Emitted by Venus: F(IR) = s Teff4
		Teff = Effective Surface Temperature of Venus
		s = Stephan's Constant = 5.67x10-8 W/m2/K4
		Surface Area of Venus = 4(pi)R2
		IIR = s Teff4[4(pi)R2]
	3.
		Determine Teff
		IIR = ISun
		s Teff4[4(pi)R2] = (1-a) F(Sun)(pi)R2
		Teff4 = a F(Sun)/(4 s)
		Teff = (0.21 x 2642 W/m2)/(4 x 5.67x10-8 W/m2/K4)
			= 222 K
		
	4. 	Without the Greenhouse effect the surface of Venus would be 222 K.
		(Earth based measurements of Temperature at cloud tops = 240 K)

Atmosphere
1. Compositon (CO2 96.5%, N2 3.5%) (Very little H2O 0.015%)!!!!!
2. Dense H2SO4 Clouds 
	- Sulphuric Acid was detemined with IR spectral reflectance. 
	- Reflectance drops quickly above 2.8 micrometre 
	(Note that at 730 K the IR wavelength of blackbody radiation is 
		2900/730 = 4 micrometre) 
	IR radiation can not escape the surface 
		(absorbed by CO2 atmosphere)
3. Thickness of Atmosphere = 50 km compared to 10km for Earth
	See figure 9.17
	
4. Circulation of the Atmosphere
	
	- Hadley Cells extend from the Equator to the Pole 
		(Earth has 3 Hadley cells)
	(Slower Rotation of 243 days versus 1 for the Earth)
		Much smaller coriolis Effect in the circulation!!!!
	- Very low wind speed on surface 0-2 m/s
	- High Circulation speeds above the clouds (50 km) 100 m/s = 360 km/hr
		Circles Venus in 4 days
	- The cloud pattern shows the swirl at the poles as the air decends
	to lower latitudes

5. Greenhouse Effect
	79% reflectance (albedo = 0.79)
	21% absorbed - (17% by H2SO4 clouds, 2% by CO2, 2% by surface)
	CO2 and H2SO4 absorbs the IR radiation and 
	it can not escape
==> Runaway effect (First Atmosphere with water vapor)
	Solar Radiation = 2 x Earth levels 
	Greenhouse Effect = C02 + H2O --> ~1400K on Surface
	- When Venus had an ocean = evaporation 
		--> more water vapor 
			--> more greenhouse gas 
				--> higher temperatures
					--> more evaporation 
	repeat

6. Loss of Water and Formation of secondary atmosphere
	- H20 evaporates to atmosphere
	- Rises to top of atmosphere
	- UV from the Sun dissociates to Hydrogen and Oxygen
	- Hydrogen lost from atmosphere (molecular speed > escape velocity)
		v(gas) ~ 3 km/s		v(escape) = 10 km/s
		6x v = 18 km/s > 10 km/s
	- CO2 baked out of the rocks = source of C02
	[Note: Earth would have atmosphere similar to Venus if all the CO2
	 were baked out of the Rocks - except for the presence of oxygen]

Surface
Radar imaging of orbiters 
	(Pioneer, Venera 15 and 16 then Magellan orbiters)
	
1. Two small 'continents' highland areas (Ishtar and Aphrodite Terra 8% of surface)
	compare the Earth with 45% of crust being continental (must include off shore)
	Ishtar has Maxwell Mountains (formed by movement of crust)
	Topo Map of Venus JPL
2. Few Craters, and only large ones (impacts only 20% of that on Lunar Maria)
	(small meteroids can not reach the surface through the thick atmosphere)
	Three Craters in Perspective JPL (same as figure 9.14)
3. No Plate Tectonics (But there are volcanic and mantle forces that move the 
	soft crust) example on the planes near Maxwell Mountains
	Destroyed Crater JPL
4. Large Volcanoes (Shield Volcanoes with very viscous lava - broad low volcanoes)
	Gula and Sif Mons (south of Maxwell) JPL (fig 9.12)
5. Large Lava Flows from cracks 
	Drainage Channel JPL
6. Broad Coronae (large raised areas due to pressure from below the crust)
	Corona Aine JPL (fig 9.13)
7. Volconic domes of thick lava
	Pancake Domes JPL
6. Young Surface ~ 0.5 billion years old - Volcanism resurfaces Venus
	Unusual Volcano and Lava Flow JPL
Theory of History of Evolution of Venus' Crust
a) Soft Crust
b) Hotter Mantle
c) Tessera formed where 'plates' collide 
	(Volcanic expansion pushes soft crust together)

Magnetic field and Solar Winds
	No Magnetic field - due to slow rotation (243 times slower than the Earth)
	Solar winds and magnetic field deflected by 
	a highly electrical conductive ionosphere
	[ The intense solar radiation ionizes the upper atmosphere to a greater 
	  extent than on Earth ]