In the field of
astronomy the term
chord typically refers to a line crossing an object which is formed during an
occultation event. By taking accurate measurements of the start and end times of the event, in conjunction with the known location of the observer and the object's
orbit, the length of the chord can be determined giving an indication of the size of the occulting object. By combining observations made from several different locations, multiple chords crossing the occulting object can be determined giving a more accurate shape and size model. This technique of using multiple observers during the same event has been used to derive more sophisticated shape models for
asteroids, whose shape can be highly irregular. A notable example of this occurred in 2002 when the asteroid
345 Tercidina underwent a stellar occultation of a very bright star as seen from
Europe. During this event a team of at least 105 observers recorded 75 chords across the asteroid's surface allowing for a very accurate size and shape determination.