3. The Moon Overview
The Earth’s only natural satellite, the Moon, rotates synchronously (the period of rotation about its axis is the same as the period of its orbit around the Earth), so that the same face is turned towards the Earth at all times.
The fundamental information about the Moon and its orbital parameters:
| Table 1 : Moon's bulk parameters | |||
|---|---|---|---|
| Moon | Earth | Moon/Earth ratio | |
| Equatorial Radius | 1738 km | 6378 km | 27 % |
| Polar Radius | 1736 km | 6357 km | 27 % |
| Mass | 7.35 x 1022 kg | 5.97 x 1024 kg | 1/81 |
| Mean Density | 3350 kg/m3 | 5515 kg/m3 | 0.607 |
| Surface Gravity | 1.62 m/s2 | 9.80 m/s2 | 1/6 |
| Table 2 : Moon's orbital parameters | |
|---|---|
| Distance from Earth (equator, km) | 378,000 |
| Semimajor axis (106 km) | 0.3844 |
| Perigee (106 km)* | 0.3633 |
| Apogee (106 km)* | 0.4055 |
| Revolution period (days) | 27.3217 |
| Mean orbital velocity (km/s) | 1.023 |
| Inclination to ecliptic (deg) | 5.145 |
| Inclination to equator (deg) | 18.28 - 28.58 |
| Orbit eccentricity | 0.0549 |
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.