Moon Fact Sheet

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Moon/Earth Comparison

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Bulk parameters

                                   Moon         Earth      Ratio (Moon/Earth)
Mass (1024 kg)                    0.07349       5.9736     0.0123   
Volume (1010 km3)                 2.1958      108.321      0.0203
Equatorial radius (km)            1738.1        6378.1    0.2725     
Polar radius (km)                  1736.0        6356.8    0.2731
Volumetric mean radius (km)        1737.1        6371.0    0.2727
Ellipticity (Flattening)          0.0012        0.00335    0.36   
Mean density (kg/m3)               3350          5515      0.607     
Surface gravity (m/s2)            1.62          9.80       0.165   
Surface acceleration (m/s2)       1.62          9.78       0.166   
Escape velocity (km/s)            2.38         11.2        0.213   
GM (x 106 km3/s2)                 0.0049        0.3986     0.0123
Bond albedo                       0.11          0.306      0.360
Visual geometric albedo           0.12          0.367      0.330   
Visual magnitude V(1,0)          +0.21         -3.86          -
Solar irradiance (W/m2)            1367.6        1367.6    1.000     
Black-body temperature (K)          274.5         254.3    1.079     
Topographic range (km)               16            20      0.800     
Moment of inertia (I/MR2)         0.394         0.3308     1.191
J2 (x 10-6)                     202.7        1082.63        0.187 

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Orbital parameters (for orbit about the Earth)

                                    Moon        
Semimajor axis (106 km)             0.3844                
Perigee (106 km)*                   0.3633
Apogee (106 km)*                    0.4055
Revolution period (days)           27.3217           
Synodic period (days)              29.53              
Mean orbital velocity (km/s)        1.023                 
Max. orbital velocity (km/s)        1.076
Min. orbital velocity (km/s)        0.964
Inclination to ecliptic (deg)       5.145
Inclination to equator (deg)       18.28 - 28.58                   
Orbit eccentricity                  0.0549             
Sidereal rotation period (hrs)    655.728               
Obliquity to orbit (deg)            6.68                  
Recession rate from Earth (cm/yr)   3.8

Mean values at opposition from Earth
       Distance from Earth (equator, km)   378,000   
       Apparent diameter (seconds of arc)     1896
       Apparent visual magnitude               -12.74    

* These represent mean apogee and perigee for the lunar orbit. 
The orbit changes over the course of the year so the distance
from the Moon to Earth roughly ranges from 357,000 km to 407,000 km.

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Lunar Atmosphere

Diurnal temperature range: >100 K to <400 K  (roughly -250 F to +250 F)
Total mass of atmosphere:  ~25,000 kg
Surface pressure (night): 3 x 10-15 bar  (2 x 10-12 torr)
Abundance at surface: 2 x 105 particles/cm3

Estimated Composition (particles per cubic cm):
   Helium 4 (4He) - 40,000 ; Neon 20 (20Ne) - 40,000 ; Hydrogen (H2) - 35,000
   Argon 40 (40Ar) - 30,000 ; Neon 22 (22Ne) - 5,000 ; Argon 36 (36Ar) - 2,000
   Methane - 1000 ; Ammonia - 1000 ; Carbon Dioxide (CO2) - 1000
   Trace Oxygen (O+), Aluminum (Al+), Silicon (Si+)
   Possible Phosphorus (P+), Sodium (Na+), Magnesium (Mg+)

Composition of the tenuous lunar atmosphere is poorly known and variable,
these are estimates of the upper limits of the nighttime ambient atmosphere
composition.  Daytime levels were difficult to measure due to heating and
outgassing of Apollo surface experiments.