Moon-pedia
  • Moon Definitions
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  • Technical Data
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  • Lunar Atmosphere
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  • Moon Reports
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  • Orbital Parameters
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  • Lunar Statistics
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    A Glossary of Moon Terms - Select a Definition Beginning With...

    | A | B | C | D | E | F | G | H | I | J | K | L | M | N | O | P | Q | R | S | T | U | V | W | X-Z |
    A
  • Albedo - Albedo is determined by measuring the ratio between the light reflected and the light shining on an object; an albedo of 1 = complete reflection.

  • Angular Diameter - The diameter of a distant object as measured by the angle formed from a point representing an observer and the outer edges of the object.

  • Annular Eclipse - An eclipse of the Sun when the Moon is farthest away in its orbit around Earth. At this point, its apparent diameter is not large enough to completely obscure the sun. During an annular eclipse, a ring of light is left uncovered around the dark circle produced by the Moon.

  • Anomalistic Month- The period of time it takes the Moon to go from one point of apogee (or perigee) to the next: 27.55455 days.

  • Anorthositic Rock- One of the types of rocks found on the Moon at higher elevations.

  • Aphelion- The point in a planet's orbit around the Sun when it is farthest from the Sun (opposite of perihelion).

  • Apogee- The point in the Moon's orbit when it is farthest from the Earth (opposite of perigee).

  • Apogean Tide The low tide of the month that occurs when the Moon is at tide apogee (farthest from Earth).

  • Apolune- The point in the orbit of an object around the Moon (such as a spacecraft) when it is farthest from the Moons surface.

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    B

  • Basalt - A type of igneous rock crated from lava and found on the luna surface in low areas, also found on earth.

  • Breccia - A composite rock found on the moon and formed from small pieces of different materials, also found on earth.

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    C

  • Celestial equator - An imaginary extension of the Earth's equator into the sky. The celestial equator is 90 degrees from each of Earth's celestial poles.

  • Celestial Mechanics - The branch of astronomy dealing with the motions and gravitational effects of celestial objects.

  • Colongitude - The longitude on the surface of the Moon marked by the terminator the edge of the area illuminated by the Sun.

  • Conjunction - The position of two celestial bodies when they are in line with one another as seen by an observer on Earth. The new moon is also referred to as moon in conjunction with the Sun (opposite of opposition).

  • Crater Wall - The circular wall formed by the impact of a meteorite on the lunar surface.

  • Crescent Moon - A phase of the Moon just before and after the new moon, when only a thin curved section is lighted by the Sun. The last crescent moon before the new moon is sometimes called the old crescent moon, and the first crescent moon is sometimes called a young crescent moon.

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    D

  • Dark of the Moon - Another name given to the new moon.

  • Declination - The angle measured between the celestial equator and an object in the sky.

  • Diurnal - A reference to a period of one day.

  • DST - Daylight Savings Time.

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    E

  • Earthshine - Reflected light from the earth. Earthshine can illuminate a young crescent moon so that the whole face can be faintly seen.

  • Eclipse - The blocking of light from the sun when the earth comes between the sun and moon or the moon between the sun and earth.

  • Ecliptic - The imaginary plane formed by the earth's orbit around the sun or the plane formed by the apparent motion of the sun through the sky.

  • Elongation - The angle of a planet away from the Sun or Moon from the Earth as viewed from Earth.

  • Ephemeris - A publication with information on how to locate the moon in the sky at a particular time.

  • Equatorial Tide - A tide produced semi-monthly by the positions of the Moon over the equator.

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    F

  • Far Side - The side of the Moon facing away from the Earth.

  • First Quarter Moon- The phase of the Moon when it is 90 degrees away from a line between the Sun and the Earth, measured east- ward from the Sun, as seen from the north. The angle of illumination creates a half circle picture of the Moons surface, with the lighted half being on the right side.

  • Full Moon - The phase of the Moon when it is on the opposite side of the Earth from the Sun and receives sunlight across its entire face, forming a circle of light. At this point, the Moon is in opposition to the Sun.

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    G

  • Gibbous Moon - The phase of the Moon when it is getting larger after the first quarter moon phase (waxing gibbous) or smaller after the full moon but before the last quarter moon (waning gibbous).

  • Gravity - One of the fundamental forces of nature, defined as the constant force of attraction between all objects in the universe. The gravitational force is inversely proportional to the square of the distance between the objects and proportional to the masses.

  • Grazing Occultation - An occultation by the Moon of a planet or star where occultation the path of the planet or star only intercepts the north or south limb of the Moon.

  • Greenwich Mean Time - Time as measured from the 0 degrees longitude position of the Greenwich Observatory in England, also known as Universal Time (UT).

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    H

  • Half Moon - The phase of the Moon also known as the quarter moon, first quarter moon, or last quarter moon.

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    I

  • Intercalation- A method of synchronizing a lunar calendar with a solar year by adding extra days or months. Extra days are known as intercalary days and extra months are known as intercalary.

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    L

  • Lacus - Latin for lake. An area on the surface of the Moon resembling a lake.

  • Last Quarter - The phase of the Moon when it is 90 degrees away moon from a line between the Sun and the Earth, measured westward from the Sun, as seen from the north. The angle of illumination creates a half circle of the Moons surface, with the lighted half being on the left side. Also referred to as the third quarter moon.

  • Latitude - Lines of measurement around a planet or the Moon, parallel to its equator. Measured in degrees, with the equator being 0 degrees and the poles 90 degrees north or south.

  • Librations - The irregular motions of the Moon in its elliptical orbit around Earth that allow slightly more than half of the Moons surface to be visible over a period of time.

  • Limb - The visible edge of a planet or moon The visible edge of a planet or moon.

  • Longitude - Lines of measurement at right angles to the equator of a planet or the Moon. Measured in degrees of angle from a designated line of 0 degrees. On the Moon, 0 degrees longitude is at the center of the visible face, in the Sinus Medii.

  • Lunar Day - The period of time between two successive transits of the Moon over the same meridian. The mean lunar day is 24-84 hours (1.035 times the mean solar day). Not the same thing as a day on the Moon, which corresponds to a synodic month.

  • Lunar Eclipse - An eclipse created by the Earth coming between the Sun and the Moon. Lunar eclipses always happen during the full moon phase.

  • Lunar Interval - The elapsed time between the transit of the Moon over the Greenwich meridian and a local meridian.

  • Lunar Rays - Visible streaks on the surface of the Moon which radiate away from some craters.

  • Lunartidal Interval - The length of time between the transit of the Moon and the following high or low tide.

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    M

  • Magnitude - A numerical value indicating the brightness of an object in space.

  • Mare - Latin for sea (plural: maria). An area on the surface of the Moon (or Mars) that is low, dark, and formed from ancient lava flows.

  • Mascon - An area of the Moons surface formed from dense, thick lunar material and having strong local gravitational effects.

  • Mean - A mathematical average of a set of numbers or measurements, with the mean equaling the sum of the numbers divided by the number of units. The mean radius of the Moon, for example, is the average radius figured from multiple measurements.

  • Meridian - An imaginary line that passes directly north and south through an observer or specified location on Earth. A plane extended from this line into space passes through the zenith (point above the observer).

  • Meteoroid - A small body drifting through space. If a meteoroid is pulled into a planet's or moons gravitational field, it is called a meteor. if the meteor survives a trip through the atmosphere and lands, it is called a meteorite. If meteorites are not burned up in the process of entering an atmosphere (or if there is no atmosphere), they may strike the surface and if large enough create a craters.

  • Moon - The natural satellite of the Earth or the natural satellite of any planet.

  • Moon Rise - The point in time when the upper limb of the Moon is even with the Earth's horizon as the Moon sets in the west.

  • Moon Set - The point in time when the upper limb of the Moon is even with the Earth's horizon as the Moon rises in the east.

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    N

  • Nadir - An imaginary point directly under an observer on the surface of the Earth, extending through the Earth and into the sky.

  • Neap Tide - The lowest high tide of the lunar month, occurring near the first and last quarter moon phases.

  • Near Side - The side of the moon facing earth.

  • New Moon - The phase of the Moon when it is directly between the Earth and the Sun. Because sunlight is hitting only the far side of the Moon, it appears dark from the Earth. Reflected light from Earth can sometimes make the new moon faintly visible.

  • Nodes - The imaginary points at which the orbital path of the Moon or other celestial body crosses the ecliptic.

  • Nodical Month - A lunar cycle measured by the Moon moving from one node and back again. A period of 27.21222 days.

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    O

  • Occulation - The movement of one celestial object behind another. Such as a star behind the moon.

  • Old Crescent Moon - Another name for the thin crescent of the Moon that is still illuminated by the Sun before the Moon goes completly dark at the new moon phase.

  • Opposition - A specific point in time when a moon or planet is 180 degrees away from the Sun, on the other side of the Earth. The Moon is full when it is in opposition (opposite of con, junction).

  • Orbital Eccentricity - The degree to which an elliptical orbit is elongated. Measured by the distance between the foci divided by the major axis.

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    P

  • Palus - Latin for swamp. An area on the surface of the Moon that is dark and resembles a swamp.

  • Parallax - The perceived movement of a distant object such as a moon, planet, or star due to the movement of the Earth.

  • Partial Eclipse- A lunar eclipse in which the Moon only partly enters the dark, umbral shadow of the Earth but is inside the secondary, penumbral shadow. Also refers to a solar eclipse when the Moon does not line up completely between the Earth and Sun and only partly obscures the Sun. This type of eclipse also produces a penumbra as well as an umbra.

  • Penumbra - The lighter part of a shadow that is formed by diffused light in an area around the edges of an object.

  • Perigee - The point in the Moons orbit when it is closest to the Earth (opposite of apogee).

  • Perigean Tide - The high tide of the month that occurs when the Moon is at tide perigee (closest to to Earth).

  • Perihelion - The point in a planet's orbit around the Sun when it is closest to the Sun (opposite of aphelion).

  • Perilune - The point in the orbit of an object (such as a spacecraft) around the Moon when it is closest to the Moons surface.

  • Phases - The visible changes that the Moon goes through in every lunar month, caused by the changing angle of illumination from the Sun. There are four specific phases - new moon, first quarter moon, full moon, and last quarter moon - and also non-specific phase names such as waxing moon, waning moon, gibbous moon, and crescent moon.

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    Q

  • Quadrature - The position of the Moon or a planet when it is at right angles to the Sun. The Moon is in first quarter phase when it is in east quadrature to the Sun and last quarter phase when it is in west quadrature.

  • Quarter Moon- The phase of the Moon that can be either the first quarter moon or the last quarter moon. This phase occurs when the Moon is 90 degrees away from a line between the Sun and the Earth. In the northern hemisphere, the angle of illumination creates a half circle picture of the Moon's surface, with the lighted half being on the right side during first quarter moon and on the left side for last quarter moon.

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    R

  • Radius - The linear measurement from the center of a sphere to the surface, or half of the diameter.

  • Regression of nodes - The backwards movement of the Moons nodes relative to the direction of orbit.

  • Revolution - The movement of one body around another in an orbit. Not to be confused with rotation.

  • Rille - A valley or small canyon on the surface of the Moon.

  • Rotation - The spinning of a body around its own axis. Not to be confused with revolution

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    S

  • Saros Cycle - A cycle of lunar months lasting 18 years and 11.3 days, the time it takes the Moon, the Earth, and the Sun to return to the same position relative to each other.

  • Satellite - An object that is in orbit around another object in space.

  • Selenography - The science dealing with the study of the surface of the Moon.

  • Selenology - The science dealing with the study of the Moon. From the Greek goddess, Selene.

  • Sidereal Month - A lunar month measured by a return to a specific position marked by a certain star: a period of 27.32166 days.

  • Sinus - Latin for bay. An area on the surface of the Moon resembling the bay of an ocean.

  • Solar Eclipse- An eclipse caused when the Moon comes directly between the Earth and the Sun, temporarily blocking out Su@s disk in the sky.

  • Spring Tide - The highest tides in a lunar month, occurring near new and full moons, when the Earth, Sun, and Moon are aligned.

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    T

  • Tektites - Small particles on the Moo@s surface made of grasslike material and formed from the impact of meteorites.

  • Terminator - The line formed by the edge of the illuminated portion of the Moon.

  • Tides - The cyclical movement of bodies of water or land on the Earth or the Moon caused by the gravitational pull of the Earth, Moon, and Sun.

  • Transit - The point when the path of the Moon, the Sun, a star, or a planet takes it across the meridian.

  • Tropical Month - The time required for the Moon to move from the first point of Aries and back: a period of 27.321582 days.

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    U

  • Umbra - The darker core of a shadow, usually cone shaped, and surrounded by a lighter penumbral shadow. Also refers to the darker center of sunspots.

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    W

  • Waning Moon - The period in the Moo@s monthly cycle after the full moon and before the new moon. During this period, the lighted portion of the Moons surface is decreasing.

  • Waxing Moon - The period in the Moo@s monthly cycle after the new moon and before the full moon. During this period, the lighted portion of the Moo@s surface is increasing.

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    X,Y,Z

  • Young Crescent Moon - Another name for the thin crescent of the Moon that is illuminated by the Sun just after the new moon.

  • Zenith - The imaginary point directly above an observer on Earth (opposite of nadir).

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    • A Moon Report (MS Word) A Moon Report (Text)
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    Lunar Statistics, Parameters and Other Technical Data
    Technical Facts...
    Mass (1024 kg)     0.07349
    Volume (1010 km3)     2.1968
    Equatorial radius (km)     1737.4
    Polar radius (km)     1737.4
    Volumetric mean radius (km)     1737.4
    Ellipticity (Flattening)     0.000
    Mean density (kg/m3)     3340
    Surface gravity (m/s2)     1.62
    Escape velocity (km/s)     2.38
    GM (x 106 km3/s2)     0.0049
    Bond albedo     0.11
    Visual geometric albedo     0.12
    Visual magnitude V(1,0)     +0.21
    Solar irradiance (W/m2)     1367.6
    Black-body temperature (K)     274.5
    Topographic range (km)     16
    Moment of inertia (I/MR2)     0.394
    J2 (x 10-6)     202.7

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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
Orbit inclination (deg)             5.145                    
Orbit eccentricity                  0.0549              
Sidereal rotation period (hrs)      655.728                
Equatorial inclination (deg)        6.68                   
Recession rate from Earth (cm/yr)   3.8

Mean values at opposition from Earth
        Distance from Earth (km)               384,467    
        Apparent diameter (seconds of arc)     1864.2
        Apparent visual magnitude              -12.74
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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.
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    Lunar Statistics

        MEAN DISTANCE OF THE        238,712 miles (384,400 km)
         MOON FROM EARTH        60.27 Earth radii
                                0.002 570 a.u.
							
GREATEST DISTANCE OF THE    	252,586 miles (406,740 km)
    MOON FROM EA(APOGEE)
	
SHORTEST DISTANCE OF THE        221,331 miles (356,410 km)
MOON FROM EARTH(PERIGEE)

           CIRCUMFERENCE    	6,790 miles (10,930 km)
                                0.27 of Earths circumference

                DIAMETER        2,160 miles (3,476 km)
                                0.27 of Earth's diameter

             MEAN RADIUS    	1,079 miles (1,737.5 km)

       EQUATORIAL RADIUS    	1,079 miles (1,738 km)

            POLAR RADIUS    	1,077 miles (1,735 km)

   MEAN ANGULAR DIAMETER      	31'07"
                                       MASS                           8 x 1019 tons (7.35 x 1022 kg)   0.0123 Earth's volume 
        
 MASS RATIO (EARTH/MOON)        81.301
                                       VOLUME                      2.4 x 103 miles3 (2.197 x 1010 km3) 0.0203 Earth's volume

                             MEAN DENSITY                      208 lb/ft3 (3.34 g/cm3)   3.33 more dense than water   0.6 Earth's density

            GRAVITY AT THE SURFACE                      5.31 ft/sec2 (1.62 m/s2)   .1667 g (1/6 Earth's gravity) 

             ESCAPE VELOCITY        1.48 miles/sec (2.38 km/sec)

MEAN INCLINATION TO LUNAR       60 41'
                  EQUATOR

 MEAN ORBITAL INCLINATION       50 08'43"
              TO ECLIPTIC

   OSCILLATION OF ORBITAL       00 9' every 173 days
   INCLINATION TO EQUATOR

     INCLINATION OF LUNAR       10 32'33"
      EQUATOR TO ECLIPTIC

     PERIOD OF REVOLUTION       3,232 days
               OF PERIGEE

        ORBITAL DIRECTION       East (counterclockwise)

       MEAN ORBITAL SPEED       2,287 miles/hour (3,683 km/hr)
                                33 minutes arc/hour
								
    DAILY SIDEREAL MOTION       13.176358 degrees
                       MEAN CENTRIPETAL                      0.01 ft/s2 (0.00272 M/s2 0.0003 g
                                       ACCELERATION 

    	
        MEAN ECCENTRICITY       0.0549 (mean eccentricity of
                 OF ORBIT       Earths orbit is 0.0167)

            SYNODIC MONTH       29.53059 days
    (NEW MOON TO NEW MOON)      29 days, 12 hr, 44 min, 2.8 sec

           SIDEREAL MONTH       27.32166 days
           (Star To Star)       27 days, 7 hr, 43 min, 11.5 sec
                                

        ANOMALISTIC MONTH       27.55455 days
     (APOGEE TO APOGEE OR       27 days, 13 hr, 18 min, 33.2 sec
      PERIGEE TO PERIGEE)

            NODICAL MONTH,      27.21222 days
           DRACONIC MONTH       27 days, 5 hr, 5 min, 35.8 sec
            (NODE TO NODE)

           TROPICAL MONTH       27.321582 days
   (1st POINT Of ARIES TO       7 days, 7 hr, 43 min, 4.7 sec
 TO FIRST POINT OF ARIES)   

      REGRESSION OF NODES       6,798 days
                                18.6247 years
                                (19.538 degrees per year)

         ROTATION PERIOD        27.321661 days
                                27 days, 7 hr, 43 min, 11.5 sec

     SURFACE TEMPERATURE        273' F (1200 C) day
                                244' F (-153' C) night
                             SURFACE AREA                      14,657,449 miles2 (37,958,621 km2)  9.4 Billion acres - 26% Larger Than Africa 

    	
         VISIBLE SURFACE        41 percent during one lunar cycle
                                18 percent additional surface
                                visible due to librations
                                59 percent total visible surface

                PARALLAX        0.9507 degrees
						 
 MOON'S ANGULAR DIAMETER        0.5181 degrees

  MAGNITUDE OF FULL MOON        -12.5

          AVERAGE ALBEDO        0.07

   ESTIMATED AGE OF MOON        4.6 billion years

  FLIGHT TIME FROM EARTH        60 to 70 hours

        INCREASE IN MEAN        1.5 inches/year (3.8 cm/year)
     DISTANCE FROM EARTH
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    Copyright © 2002 By Keith Cooley