Flag Reference #

Flags are bitmasks that control what is calculated and how results are returned. calc_ut() / calc() return a 6-element tuple (longitude, latitude, distance, speed_lon, speed_lat, speed_dist) and a return flag. Combine flags with |.

Velocity #

Flag	Effect
`SEFLG_SPEED`	Populate speed fields (pos[3]-pos[5]) with daily motion. Without this, speeds are zero. Almost every call should include it.

Observer #

By default the observer is at Earth’s center (geocentric).

Flag	Effect
`SEFLG_HELCTR`	Heliocentric: observer at the Sun. Distances become heliocentric AU.
`SEFLG_BARYCTR`	Barycentric: observer at the solar system barycenter.
`SEFLG_TOPOCTR`	Topocentric: observer on Earth’s surface. Set position with `set_topo(lon, lat, alt)`. Matters most for the Moon (~1 deg parallax).

Coordinates #

By default output is ecliptic longitude/latitude of date.

Flag	Effect
`SEFLG_EQUATORIAL`	Right Ascension (0-360 deg) and Declination (+/-90 deg) instead of ecliptic coordinates.
`SEFLG_XYZ`	Cartesian (x, y, z) in AU instead of spherical coordinates.
`SEFLG_RADIANS`	Angles in radians instead of degrees.

Reference Frame #

By default positions are precessed to the equinox of date.

Flag	Effect
`SEFLG_J2000`	J2000.0 reference frame (no precession to date).
`SEFLG_NONUT`	Mean ecliptic/equator (no nutation applied).
`SEFLG_ICRS`	ICRS frame (no precession, no nutation, no frame bias).

Position Corrections #

By default positions are apparent (light-time + aberration corrected).

Flag	Effect
`SEFLG_TRUEPOS`	Geometric position: no light-time correction.
`SEFLG_NOABERR`	Astrometric: light-time corrected, no aberration.
`SEFLG_NOGDEFL`	Skip gravitational deflection correction.
`SEFLG_ASTROMETRIC`	Shorthand for `SEFLG_NOABERR \| SEFLG_NOGDEFL`.

Sidereal Zodiac #

Flag	Effect
`SEFLG_SIDEREAL`	Subtract ayanamsha from ecliptic longitude. Requires prior `set_sid_mode()` call to select ayanamsha (Lahiri, Fagan-Bradley, etc.).

Compatibility #

Flag	Effect
`SEFLG_MOSEPH`	Accepted for API compatibility, silently ignored. All calculations always use JPL DE440/DE441.
`SEFLG_SWIEPH`	Same – accepted and ignored.
`SEFLG_SPEED3`	Converted to `SEFLG_SPEED` internally.

Examples #

import libephemeris as swe
from libephemeris.constants import *

jd = swe.julday(2024, 3, 26, 12.0)

# Default: geocentric ecliptic apparent position with speed
pos, _ = swe.calc_ut(jd, SE_MARS, SEFLG_SPEED)

# Heliocentric with speed
pos, _ = swe.calc_ut(jd, SE_MARS, SEFLG_SPEED | SEFLG_HELCTR)

# Sidereal equatorial
swe.set_sid_mode(SE_SIDM_LAHIRI)
pos, _ = swe.calc_ut(jd, SE_SUN, SEFLG_SPEED | SEFLG_SIDEREAL | SEFLG_EQUATORIAL)

# J2000 ecliptic, no aberration
pos, _ = swe.calc_ut(jd, SE_MOON, SEFLG_SPEED | SEFLG_J2000 | SEFLG_NOABERR)

# Topocentric (Rome)
swe.set_topo(12.4964, 41.9028, 0)
pos, _ = swe.calc_ut(jd, SE_MOON, SEFLG_SPEED | SEFLG_TOPOCTR)