The earth has a single MOON that orbits it at a distance of 238,855 miles. The moon is kept in orbit by the gravitational force of the earth. Because of this gravitational force, the moon orbits the earth on the same fixed side while the further side is the far or dark side which has only been seen by space probes and astronauts. The temperature ranges from 253 ºF when the sun is not shinning to -261 ºF during sunny temperature on the moon.
Most scientists and astronomers think the moon was formed when massive objects, with size of small planets collided. These may have cause enormous amount of rocky debris when joined together, formed a single mass called the MOON.
Phases of the MOON
An image of a full moon captured at 11:00 PM CDT from the Eastern horizon during Lunar Halo.
Moon Earth Ratio (Moon/Earth) Mass (1024 kg) 0.07342 5.9726 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) 3344 5514 0.606 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) 270.7 254.3 1.064 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
Apogee and Perigee of the Moon
Apogee and perigee refer to the distance from the Earth to the moon. Apogee is the farthest point from the earth. Perigee is the closest point to the earth and it is in this stage that the moon appears larger. Looking at the moon in the sky without anything to compare it to, you wouldn’t notice any size difference. But the difference in size can in fact be quite significant.
If you were to photograph a full moon at apogee and perigee (using the same lens), here’s how the two sizes would compare:
Astronomers have formulas for computing the exact distance at any point in time, but the average distance from Earth is 237,700 miles (382,500 km).
Effects of Apogee and Perigee
The apogee and perigee of the moon have an effect on the tides here on Earth. When the moon is at apogee, the furthest distance from the Earth, it has less gravitational pull which, along with other factors that influence the tides, can contribute to lower tides or lower variation in the high/low tide level. When the moon is at perigee, closer to the Earth, there is much more gravitational pull which contributes to the opposite effect: higher tides or greater variation in the high and low tide.
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) 1.022 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.
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.