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Understand near-Earth asteroids

Short, accurate guides on the science behind the numbers you see in the Orbitfall tracker.

NASA's PHA label means an asteroid is worth watching — not that it's on a collision course. Here's what the classification actually means.

One lunar distance equals the average Earth–Moon gap, 384,400 km. Astronomers use it as a natural yardstick for close approaches.

A close approach is a scheduled flyby, not a near miss. Here's how NASA defines the term and why most close approaches are routine.

From first-night detection to CNEOS Sentry impact monitoring, here's how new near-Earth objects are discovered, confirmed, and watched.

Three words for three very different things. A quick, honest guide to the difference between asteroids, meteors, and comets.

NEO, PHA, MOID, LD, absolute magnitude, and other terms — defined.

How we rank how notable each close approach is — and why it's not an impact prediction.

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