Celestial mechanics

mean distance between Earth and the Sun, common length reference in astronomy

right|thumb|Variation of orbital eccentricity    

mysterious non-luminous matter (and/or radiation) comprising most of the matter in our observable universe

branch of astronomy

situation in which an astronomical object's orbital period matches its rotational period

field of classical mechanics concerned with the motion of spacecraft

astrophysical process in which matter gravitationally collects into a massive object

days since the beginning of the Julian Period

in astronomy, angular separation between the Sun and a planet, with the Earth as a reference point

thumb| Upper (oK) and lower culmination (uk) thumb|Method of observation of culminations in ancient Egypt In observational astronomy, culmination is the passage of a celestial object (such as the Sun, the Moon, a planet, a star, constellation or a deep-sky object) across the observer's local meridian. These events are also known as meridian transits, used in timekeeping and navigation, and measured precisely using a transit telescope.

gravity-induced, slow, and continuous change in the orientation of an astronomical body's rotational axis

complex motion of a massive astronomical body

thumb|right|200px |A circle of radius compressed to an ellipse. thumb|right|200px |A sphere of radius compressed to an oblate ellipsoid of revolution.

pressure exerted upon any surface exposed to electromagnetic radiation

small natural satellite associated with a planetary ring

center of mass of two or more bodies that are orbiting each other, or the point around which they both or all orbit

motion in space when there is fixed line of points

alternative explanation of the non-Newtonian rotation of galaxies

aspect of a heavenly body in which it makes a right angle with the direction of the Sun

astronomical phenomenon when a planet or other stellar satellite interacts with a disk of gas or planetesimals, resulting in the alteration of the satellite's orbital parameters, especially its semi-major axis

possible non-random component of the peculiar velocity of galaxy clusters

system of two astronomical bodies which orbit each other

spacecraft propulsion system which uses electricity

return of a perturbed system into equilibrium

criterion for a celestial body to be considered a planet

A strangelet (pronounced ) is a hypothetical particle consisting of a bound state of roughly equal numbers of up, down, and strange quarks. An equivalent description is that a strangelet is a small fragment of strange matter, small enough to be considered a particle. The size of an object composed of strange matter could, theoretically, range from a few femtometers across (with the mass of a light nucleus) to arbitrarily large. Once the size becomes macroscopic (on the order of meters across), such an object is usually called a strange star. The term "strangelet" originates with Edward Farhi a

in astronomy, the statistical dispersion of velocities about the mean velocity for a cluster of stars or galaxies

cosmic dust and debris orbiting an astronomical body

Concept in astrophysics

proportionality of orbital periods for two celestial bodies

spatial distribution of mass within a solid body

Procedure to determine asteroid masses

periodic perturbation of the lunar orbit