Glossaire beginning with A
Fraction of sunlight reflected or scattered by a planet or a comet. The albedo of cometary nuclei, which are very dark, is generally less than 0.1.
- The point of the orbit of a planet or comet where it is farthest from the sun.
- Small solid body belonging to the Solar system; most asteroid orbits are located between that of Mars and that of Jupiter.
- Measurement of position, of apparent movements and of distance of celestial objects (comets, planets, satellites, stars, etc.).
- Astronomical Unit (AU or a.u.)
- Unit of length equal to the semi-major axis of Earth's orbit (150 million kilometers).