Orbit of the MoonThe orbit of the Moon is, while stable and known, highly complex, and as such still studied by lunar theory. Most models describe the Moon's orbit geocentrically since the Moon is mainly bound to Earth, but it also orbits together with Earth, as the Earth–Moon system, around their shared barycenter. Furthermore from a heliocentric view its geocentric orbit is the result of Earth perturbing the Moon's orbit around the Sun.
Cassini's lawsCassini's laws provide a compact description of the motion of the Moon. They were established in 1693 by Giovanni Domenico Cassini, a prominent scientist of his time. Refinements of these laws to include physical librations have been made, and they have been generalized to treat other satellites and planets. Cassini's lawsThe Moon has a 1:1 spin–orbit resonance.
Tidal lockingAt left, tidally locked, the Moon rotates at the same rate it orbits the Earth, keeping the same face toward the planet. At right, not tidally locked, if the Moon did not rotate then the face would change over the course of an orbit. Viewed from north; not to scale.A side view of the Pluto–Charon system.
Orbital eccentricityIn astrodynamics, the orbital eccentricity of an astronomical object is a dimensionless parameter that determines the amount by which its orbit around another body deviates from a perfect circle. A value of 0 is a circular orbit, values between 0 and 1 form an elliptic orbit, 1 is a parabolic (escape orbit or capture orbit), and greater than 1 is a hyperbola. The term derives its name from the parameters of conic sections, as every Kepler orbit is a conic section.
Ecliptic coordinate systemIn astronomy, the ecliptic coordinate system is a celestial coordinate system commonly used for representing the apparent positions, orbits, and pole orientations of Solar System objects. Because most planets (except Mercury) and many small Solar System bodies have orbits with only slight inclinations to the ecliptic, using it as the fundamental plane is convenient.
EarthThird planet from the SunSurface equivalent doserate0.274 μSv/hAbsolute magnitude (H)−3.99AtmosphereSurface pressure101.325 kPa (at sea level)Composition by volume78.08% nitrogen (dry air)20.95% oxygen (dry air)≤1% water vapor (variable)0.9340% argon0.0430% carbon dioxide0.00182% neon0.00052% helium0.00017% methane0.00011% krypton0.00006% hydrogen Source:Earth is the third planet from the Sun and the only astronomical object known to harbor life.
MoonNatural satellite orbiting EarthSurface absorbed doserate13.2 μGy/h(during lunar daytime)Surface equivalent doserate57.0 μSv/h(during lunar daytime)Apparent magnitude−2.5 to −12.9−12.74 (mean full moon)Absolute magnitude (H)0.2Angular diameter29.3 to 34.1 arcminutesAtmosphereSurface pressure10 Pa (1 picobar) (day)10 Pa (1 femtobar) (night)Composition by volumeHeArNeNaKHThe Moon is the only natural satellite of Earth.
Lagrange pointIn celestial mechanics, the Lagrange points (), also called the Lagrangian points or libration points, are points of equilibrium for small-mass objects under the gravitational influence of two massive orbiting bodies. Mathematically, this involves the solution of the restricted three-body problem. Normally, the two massive bodies exert an unbalanced gravitational force at a point, altering the orbit of any other celestial body at that point.
Lunar distanceThe instantaneous Earth–Moon distance, or distance to the Moon, is the distance from the center of Earth to the center of the Moon. In contrast, the Lunar distance (LD or Δ ⊕ L {\textstyle \Delta _{\oplus L}} ), or Earth–Moon characteristic distance, is a unit of measure in astronomy. More technically, it is the semi-major axis of the geocentric lunar orbit. The average lunar distance is approximately 385,000 km (239,000 mi), or 1.3 light-seconds.
Angular diameterThe angular diameter, angular width, angular size, apparent diameter, or apparent size is an angular separation (in units of angle) describing how large a sphere or circle appears from a given point of view. In the vision sciences, it is called the visual angle, and in optics, it is the angular aperture (of a lens).
Tidal forceThe tidal force or tide-generating force is the difference in gravitational attraction between different points in a gravitational field. It causes different parts of bodies to be pulled unevenly, so that those bodies are being stretched towards the attraction. Tidal force is the differential effect of gravity across an extended body. Rather than the total gravitational force, it is the spatial variation in that force.
Trojan (celestial body)In astronomy, a trojan is a small celestial body (mostly asteroids) that shares the orbit of a larger body, remaining in a stable orbit approximately 60° ahead of or behind the main body near one of its Lagrangian pointsL4 and L5. Trojans can share the orbits of planets or of large moons. Trojans are one type of co-orbital object.
hemisphereRelated word or term.librationRelated word or term.*As an Amazon Associate I earn from qualifying purchases.