API Reference / riseSet · function
Function: riseSet()
function riseSet(
engine,
body,
jdStart,
latDeg,
lonDeg,
kind?,
opts?): number | null;
The next rise, set, or meridian transit of a body after jdStart, as a
Julian Day (UT). Accounts for the body's apparent radius, atmospheric
refraction, and observer altitude.
Parameters
| Parameter | Type | Default value | Description |
|---|---|---|---|
engine | Engine | undefined | The engine used to evaluate positions. |
body | BodyId | undefined | A body id from Engine.bodies. |
jdStart | number | undefined | Search start, Julian Day (UT). The result is the first event strictly after this instant. |
latDeg | number | undefined | Observer latitude in degrees, north positive. |
lonDeg | number | undefined | Observer longitude in degrees, east positive. |
kind | RiseKind | "rise" | "rise", "set", "mtransit" (upper/meridian transit), or "itransit" (lower transit). Defaults to "rise". |
opts | RiseSetOptions | {} | altM (observer altitude, m), pressure (hPa), tempC, and searchDays (how far ahead to look; defaults to 2). |
Returns
number | null
The event time as a Julian Day (UT), or null when it does not
occur in the window (e.g. polar day or night).
Example
// Next sunrise over London after 2025-06-01
const jd = riseSet(engine, "sun", julianDay(2025, 6, 1), 51.5, -0.13, "rise");