tracklet

Asteroids look exactly like stars in a single image. What gives one away is that it moves, so a survey telescope photographs the same patch of sky several times in a night, removes everything that stays still, and links what is left into short runs of detections. Each of those runs is a tracklet: a set of observations of what is taken to be one object, made on one night. The Planetary Science Journal describes that linking as the step that turns raw detections into something the scientific community can archive and use, and notes that the Minor Planet Center will not normally accept single observations at all.

A tracklet has to contain at least two observations, and three or four are preferred, because two points can be joined by accident and a false link puts a phantom object into the catalogue. Observers assemble their own tracklets before submitting them, by hand or with linking software. On arrival each tracklet is checked against the orbits of objects already on record. If it matches one, the observations are attached to that object and no new designation is made. If it does not, a preliminary orbit is fitted and that fit decides whether anything new has been found.