In celestial mechanics, an orbit is the trajectory followed by a planet to respond to the gravitational effect of its star. The orbit corresponds to the curvature of space generated by gravitational forces. The four-dimensional fabric of space-time "resembles" the surface of a trampoline, distended by planets and stars. It is this warping, or curvature of spacetime, that creates what feels like gravity.
In the solar system, all planets, asteroids and comets orbit the Sun. Similarly, around planets, natural or artificial satellites follow the curvature of space and follow an orbit around their planet.
No orbit is perfectly circular or perfectly coplanar around the Sun's equator. Orbits have a perihelion (closest point to the Sun), an aphelion (farthest point from the Sun) and an inclination (angle relative to the plane of the Sun's equator).
Note: The Apoapside is the furthest point between a celestial object and the focus of the orbit.
Apogee is the farthest point between a satellite and Earth.
Aphelion is the farthest point between a celestial object and the Sun.
Objects | Semi-major axis |
Mercury | 57 900 000 km |
Venus | 108 200 000 km |
Earth | 149 600 000 km |
Mars | 227 900 000 km |
Jupiter | 778 410 000 km |
Saturn | 1 427 000 000 km |
Uranus | 2 870 000 000 km |
Neptune | 4 496 000 000 km |
NB: The Periapsis is the closest point between a celestial object and the focus of the orbit.
Perigee is the closest point between a satellite and the Earth.
Perihelion is the closest point between a celestial object and the Sun.