### A

**Apocentre:**This is the point of an elliptical orbit, which is the furthest from the parent body.
**Ascending node:** This is an intersection between the orbit and the reference plane.
**AU:** Stands for Astronomical Unit. This is the mean distance between the Sun and the Earth, i.e. 149,597,870.700 km

### B

### C

**Chaos:** A trajectory is chaotic when, at some point, you cannot accurately predict it.
**Circulation:** An angle is circulating when it can take any number between 0° and 360°.

### D

### E

**Eccentricity:** This parameter characterizes the elongation of a trajectory. Eccentricity e = 0 means that the trajectory is circular. Elliptical orbits have always e < 1.

### F

### G

### H

**Hamiltonian:** Total energy of a dynamical systems, expressed with convenient (canonical) variables, which mathematical properties permit an in-depth analysis of the dynamics. In the absence of dissipation, the Hamiltonian is constant.

### I

### J

### K

**Kozai-Lidov mechanism:** Dynamical mechanism raising the inclination of a body, when eccentric enough. This results in the libration of the difference between its pericentre and its ascending node.

### L

**Longitude (orbital):** It is an angle determining the emplacement of a body on its orbit.

### M

**Mass wasting:** Bulk movement of rock debris and / or soil down slope due to gravity.

### N

### O

**Orbit:** Trajectory of a body.

### P

**Parent body:** The body around which a given body moves. The parent body of the Earth is the Sun, the parnt body of the Moon is the Earth.
**Pericentre:** This is the point of an elliptical orbit, which is the closest from the parent body.

### Q

### R

**Resonance:** Equality between two independent frequencies of a given dynamical system. This results in a raise of the response, pushing a dynamical parameter like the eccentricity, the inclination…

### S

### T

**Three-body problem:** The motion of 3 bodies, interacting with each other. When one of these bodies is so small that it is assumed to not affect the other ones, we speak of the restricted 3-body problem.
**Tides:** Differential gravitational action of an outer body on another one, with a finite size. This results in stress and strains which alter the shape of the body, and energy dissipation, which also affects its rotation and its orbit.

### U

### V

### W

### X

### Y

### Z

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