Fr.: distance polaire
The angular distance of an object from a celestial pole. It is equal to 90° minus the object's declination.
Fr.: distance propre
A distance between two nearby events in the frame in which they occur at the same time. It is the distance measured by a ruler at the time of observation. Hence, for a cosmological time t, Dproper = DC . a(t), where DC is the → comoving distance, and a(t) is the → scale factor. In the present epoch a = a(tobs) = 1, and Dproper = DC.
proper motion distance
durâ-ye jonbeš-e saré
Fr.: distance mouvement propre
The distance derived from the → proper motion of an object. If an object has a known → transverse velocity u, and has an observed angular motion of dθ/dt, then the proper motion distance is defined as: d = u/(dθ/dt).
Fr.: relation décalage vers le rouge-distance
The correlation, first established by E. Hubble, between the cosmological recession velocities of galaxies and their distances.
time delay distance
apest-e derang-e zamâni
A distance-like quantity derived from → gravitational lensing time delay. It is given by a combination of three angular diameter distances in a strong lens system: DΔt = (1 + zL)[DA(EL)DA(ES) / DA(LS)], where zL is the → redshift of the → gravitational lens, while DA(EL), DA(ES), and DA(LS) are the angular diameter distances from the Earth to the lens, from the Earth to the source, and from the lens to the source, respectively. As each of the distance is proportional to the inverse of H0, DΔt is proportional to 1/H0.
Fr.: relation vitesse-distance
The linear relation wherein all galaxies are moving away from one another, with velocities that are greater with increasing distance of the galaxy. Same as → Hubble's law.
durâ-ye sarsu, duri-ye ~
Fr.: distance zénithale
The angular distance of a celestial body from the zenith. The zenith distance is 90° minus the body's altitude above the horizon (i.e. the complement of the altitude) and hence is also known as coaltitude.