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Lunar Facts & Figures

1. Physical (Size) Constants
   • Diameter = 3476 km, Circumference = 10920 km
   • Mass = 0.01226 x earth's
   • Volume = 0.0203 x earth's
   • Density = 3.34 x 106 kg/m3
   • Oblateness = 0.0005
   • Gravity = 0.16 x earth's
   
   
2. Environmental Parameters
   • Atmosphere < 8 x 10-9 torr (surface, daytime) [He, H2, Ne, Ar,...]
   • Mean surface temperatures = 107 C day; -153 C night
   • Expected extremes = 130 C day; -180 C night
   • Direct solar radiation = 107 rad/m2/year
   • Electrostatical levitation (mostly to 30cm) by the terminator is 300 g/m2 /yr
   • 30 million lunar secondary ejecta that are 1 ng or bigger are suspended with a velocity of 1 km/s, which means roughly 10-1 g/m2 /yr
   
   
3. Astronomical Constants
   • Mean distance from earth = 0.3844 x 106 km
   • Mean distance from Sun = 1 Au (149.6 x 106 km)
   • Inclination of axis = 6o41' relative to earth
   • Period of revolution about earth = 27.32 earth days
   • Period of rotation = 27.32 earth days
   • Insolation = 1358 W/m2
   
   
4. Observations
   • Mean apparent diameter of Sun from moon = 31'59"
   • Mean apparent diameter of moon from earth = 31'59" (approx)
   • Mean apparent diameter of earth from moon = 62'27" (approx)
   
   
5. Terrain Characteristics
   • Mostly benign equivalent to 1.5o rigid slope in terms of mobile resistance (Ref[HEIKEN91A])
   • Slope angle of repose of soil: ~ 40o
   • Apollo 11 site crater (D: diameter, y: depth, h: rim height, y ~ 0.2 D, h ~ 0.2 y, D < 13 km)
     • D > 1 m: 10 craters/ 100 m2
     • D > 3 m: 0.4 craters/ 100 m2
     • D > 5 m: 0.1 craters/ 100 m2
   • Surveyor 3 site (similar to Apollo 11 site) boulder (h: height)
     • h > 25 cm: 3 ~ 4/ 100 m2
     • h > 50 cm: 1 / 100 m2
     • h > 1 m: 0.1 / 100 m2
     
     
   • Very soft soil in the vicinity of large crater sides
   • Skyline marked by tall mountains
   • Loose top soil with rapidly increasing compaction with depth
   • Apollo lander dug in 50 cm and Armstrong's footprints were 20 cm deep
   
   
6. Dust Quantification
   • Surface is covered with fine positively charged electrostatic dust
   • Electrostatic levitation by terminator is 300 g/m2/yr
   • 30 M secondary ejecta, 1 ng or bigger are suspended with a speed of 1 km/s. Rough deposit rate is 10-1 g/m2/yr
   
   

The terminator refers to the line dividing sunlight and darkness. This line is sharp and distinct due to absence of an atmosphere. Moving across the equator at a super-highway speed, the terminator energises the dust particles kicking up dust, and positively charging it on the bright side.