# Glossary

### 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

### 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°.

### 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.

### 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.

### 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.

### O

• Opposition: Alignment between the Sun, the Earth, and the object we study.
• 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.

### 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…

### 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.