An Etymological Dictionary of Astronomy and Astrophysics

1. The separation/length in space/time between two things/events.
   

   2. The state of being apart in space or time.
      

2. In cosmology four main distance definitions are used: → luminosity distance, → angular diameter distance, → comoving distance, and → light-travel distance.

In a → flat Universe these four approaches give the same result for the present epoch for distances below 100 Mpc. In a non-flat Universe with the → Robertson-Walker metric they give different but related values.

See also:
→ apparent distance, → cosmic distance scale, → cosmological distance, → distance function, → distance modulus, → distance to the horizon, → focal distance, → Hubble distance, → perihelion distance, → polar distance, → proper distance, → redshift-distance relation, → velocity-distance relation, → zenith distance.

Etymology (EN): M.E., from O.Fr., from L. distantia “a standing apart,” from distantem (nominative distans) “standing apart, separate, distant,” pr.p. of distare “to stand apart,” from → dis- “apart, off” + stare “to stand,” (cf. Mod.Pers. istâdan “to stand,” O.Pers./Av. sta- “to stand, stand still; set,” Skt. sthâ- “to stand,” Gk. histemi “put, place, weigh,” stasis “a standing still”).

Etymology (PE): Apest, literally “standing apart,” from apa- prefix denoting “separation, away, off,” → dis-, + est variant of ist, present stem of istâdan, to stand," as above;" cf.
Choresmian bst “to stand apart,” from *apa- + st- “to stand,” → stand.
Durâ, duri, noun from dur “far, distant, remote,” Mid.Pers. dur, O.Pers. dūra- “far (in time or space),” Av. dūra-, from dav- “to move away,” cf. Skt. dūrá- “distant, far.”