Glossary

The terminology you'll run into in NASA data and across the Orbitfall tracker.

NEO — Near-Earth Object: Any small solar-system body — asteroid or comet — whose orbit brings it within 1.3 astronomical units of the Sun, and therefore relatively close to Earth's orbit.
PHA — Potentially Hazardous Asteroid: A near-Earth asteroid whose Minimum Orbit Intersection Distance with Earth is 0.05 AU or less and whose absolute magnitude is 22.0 or brighter (roughly 140 m or larger). A monitoring category, not a prediction.
MOID — Minimum Orbit Intersection Distance: The minimum distance between two orbits — for near-Earth asteroids, the closest that the asteroid's orbit ever comes to Earth's orbit, independent of where either body actually is at that moment.
Lunar Distance (LD): 384,400 km — the average distance between the centers of Earth and the Moon. Widely used as an intuitive yardstick for asteroid close-approach distances.
Absolute Magnitude (H): A brightness measure for small bodies, defined as the apparent magnitude the object would have if it were 1 AU from both the Sun and the observer. Lower H means brighter and, for a given surface reflectivity, larger.
Miss Distance: The closest predicted distance between an asteroid and Earth during a given close approach. Reported in kilometers, astronomical units, and lunar distances.
Close Approach: The moment an asteroid or comet reaches its minimum distance to Earth on a given pass. A scheduled flyby with a known trajectory — not a near miss.
NeoWs — Near Earth Object Web Service: NASA's public HTTP API for near-Earth object data, exposing close-approach records and object details maintained by CNEOS at JPL.
Perihelion: The point in an orbit closest to the Sun. For a near-Earth asteroid, its perihelion distance determines whether its orbit crosses inside Earth's.
Aphelion: The point in an orbit farthest from the Sun. Together with perihelion, it defines the shape and reach of the orbit.