Orbital elements
Orbital elements are the six numbers that describe the size, shape and orientation of an orbit and where an object is on it.
Astronomers describe an orbit with six orbital elements. The semi-major axis gives the orbit's size, measured as half its longest width. The eccentricity gives its shape, from 0 for a circle to nearly 1 for a very stretched ellipse. The inclination is the tilt relative to Earth's orbital plane. Two angles, the longitude of the ascending node and the argument of perihelion, describe how the orbit is turned in space. The sixth element pins down where the object is on its orbit at a given time.
With these numbers, an object's position can be predicted years ahead. When cameras film a fireball, scientists calculate the meteoroid's orbital elements before it met Earth. Most turn out to have semi-major axes of about 1.5 to 3 astronomical units and low inclinations, pointing back to the inner asteroid belt.
Comparing orbits of meteorites with those of asteroid families can identify their likely source regions.
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