Beschreibung:
<jats:p>A Lorentzian space-time (M,g), along with an observer field (=timelike vector field) V, are considered. Several theorems are presented that are concerned with the redshift and parallaxes in such a model. Here the term ‘‘parallaxes’’ stands for the relative motion of two observers at the celestial sphere of a third observer. As an important mathematical tool, the index form along a lightlike geodesic is used.</jats:p>