API Reference / pheno · function

Function: pheno()

function pheno(
   engine, 
   body, 
   jdUt): Pheno;

Photometric and apparent-geometry quantities for a body at an instant: its phase angle, illuminated fraction, elongation from the Sun, apparent disc diameter, and apparent visual magnitude.

Parameters

Parameter	Type	Description
`engine`	`Engine`	The engine used to evaluate positions.
`body`	`BodyId`	A body with known physical dimensions (Sun, Moon, the planets).
`jdUt`	`number`	Julian Day (UT).

Returns

Pheno

A Pheno: phaseAngle (deg), phase (lit fraction 0–1), elongation (deg), diameter (deg), and magnitude.

Throws

Error if body has no photometric data.

Example

pheno(engine, "venus", julianDay(2025, 6, 1)).phase; // illuminated fraction

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