Chord (astronomy)

In the field of astronomy the term chord typically refers to a line crossing an object which is traversed during an occultation event.

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.

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.

Knowing these two locations, combined with the direction to the background object, the two endpoints of the chord can be determined using simple geometry.