An Etymological Dictionary of Astronomy and Astrophysics
English-French-Persian

The distance traversed by a photon between the time it is emitted and the time it reaches the observer. It is also referred to as the → look-back time.

→ light; → travel; → distance.

1) The act of traveling, especially to a distant place.
2) To go, move, or journey from one place to another.

M.E. from travailen "to make a journey," originally the same word as Fr. travail "work, labor" (by shift to "make a laborious journey").

Safar, from Ar.

(British: traveller) A person or thing that travels.

→ travel; → -er.