English (United Kingdom)

https://curated-unify.zendy.io/wp-json/zendy-region/v1/featured_content/oa?rat=en

https://curated-unify.zendy.io/wp-json/zendy-region/v1/highlighted_journal/

Global: Zendy Plus annual

Presents the access of premium content as premium feature

Premium Content

Presents the keyphrase highlighting as premium feature

Keyphrase Highlighting

Presents the summarisation as premium feature

Summarisation

Insights

Presents the pdf analysis as premium feature

PDF Analysis

Presents the zaia usage as premium feature

ZAIA

Global: Zendy Tools annual

Global: Zendy Free Plan

Global: Zendy Tools monthly

Global: Zendy Plus monthly

We present a covariant approach to the problem of light beam propagation in cosmological models within the framework of classical geometric optics in general relativity. Using the concept of screen surface orthogonal to the observer’s world-line and to the bundle of geodesics, we introduce covariant four-dimensional definitions and derive propagation equations for Sachs and Jacobi optical fields and for the area distance.

Covariant Formulation of Light Propagation in Cosmological Models