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

A particular extent of space or surface; the scope of a concept, operation, or activity.

The etymology is not clear; perhaps akin to L. arere "to be dry" → arid.

Pahné "area, field," from pahn "broad, wide" (Mid.Pers. pah(a)n, Av. pathana- "broad, wide, spacious," probably related to perethav- "broad, wide," Skt. prthav-, Gk. platus; PIE *plat- "to spread") + noun forming suffix -é.

Of an → electromagnetic wave, the area of a surface perpendicular to the direction of → propagation, over which the wave maintains a specified → degree of coherence. According to the van Cittert-Zernike theorem, the coherence area is given by: A_c = D²λ²/(πd²), where d is the diameter of the light source and D is the distance away. The coherence area is an important parameter in photon correlation experiments. In the → Young's experiment the → interference pattern is only seen if slits are inside one coherence area.

→ coherence; → area.

Of an interferometric telescope made up of several mirrors, the hypothetical mirror created by the combination of the individual mirrors.

→ collect; → area.