CesiumJS Time Properties

---
name: cesiumjs-time-properties
description: "CesiumJS time, properties, and animation - Clock, JulianDate, TimeInterval, Property, SampledProperty, CallbackProperty, interpolation, splines, CZML temporal data. Use when making entity attributes time-dynamic, configuring the simulation clock, interpolating positions over time, or working with sampled or callback properties."
---
# CesiumJS Time, Properties & Animation

Version baseline: CesiumJS v1.142

Covers the temporal data-binding layer: Clock/JulianDate time system, the Property hierarchy that makes entity attributes change over time, interpolation algorithms, splines, and material properties. Properties live here (not with Entities) because SampledProperty and CallbackProperty are meaningless without Clock/JulianDate. The Material class (Fabric) belongs in cesiumjs-materials-shaders.

## JulianDate -- The Time Primitive

Stores whole days + fractional seconds separately for precision. Always uses TAI internally.

```js
import { JulianDate } from "cesium";

// Creation: fromIso8601 (most common), fromDate, now
const date = JulianDate.fromIso8601("2025-06-15T12:00:00Z");
const jd = JulianDate.fromDate(new Date("2025-06-15T12:00:00Z"));
const now = JulianDate.now();

// Conversion: toIso8601, toDate, toGregorianDate
const iso = JulianDate.toIso8601(date); // "2025-06-15T12:00:00Z"
const greg = JulianDate.toGregorianDate(date); // {year, month, day, hour, ...}