What is an FMO versus a VFMO?
A. The term FMO was coined when a fast moving NEA was discovered in the old days of photographic discoveries. Fast referred to objects moving faster than local main belt asteroids and up to speeds of several degrees per day. On the long exposures (up to an hour in those days) even relatively slow objects left long trailed images, thus really fast objects would just be a line across the plate (no endpoints) – without endpoints, an object’s speed could not be determined and therefore the orbit could not be parameterized for the purpose of followup. Exposure times shortened substantially when CCDs replaced photographic plates (Spacewatch’s exposure time is about 2.5 minutes.) These shorter exposure times meant shorter trails, hence the endpoints of a faster object trail became visible and thus measureable. Spacewatch was the first program to use CCD technology for the discovery of asteroids. When Spacewatch discovered its first long trailed object in its exposures, it was moving about 20
