A near-Earth object is an asteroid or comet whose orbit comes within about 1.3 astronomical units of the Sun — close enough that part of its path lies near Earth’s own orbit. Almost all are near-Earth asteroids: chunks of rock and metal, most far smaller than a city block, nudged onto these orbits over millions of years by collisions and the gravity of the planets.
A “close approach” is simply the moment an object reaches its nearest point to Earth on a given pass. Astronomers measure that miss distance in two units: lunar distances (1 LD = 384,400 km, the average Earth–Moon gap) and astronomical units (1 AU ≈ 149.6 million km, the average Earth–Sun gap). A flyby at 20 lunar distances is a routine event; even a “very close” pass of 1 LD is still farther than the Moon.
The word “close” causes most of the needless alarm. On any given week, dozens of catalogued asteroids reach their close-approach points, and the overwhelming majority pass at distances of millions of kilometres — tens to hundreds of times the distance to the Moon. A pass inside the Moon’s orbit makes news precisely because it is uncommon, and even then the object sails by without touching the atmosphere.
Close approaches are predictable. Once an asteroid’s orbit is well measured, its position can be projected years and often decades ahead, which is how observatories publish flyby dates and miss distances in advance. A close approach on the calendar is not a warning — it is the product of orbital mechanics working exactly as expected.