lib_vsop87_mercury

Library "lib_vsop87_mercury"
Heliocentric and geocentric position calculations for Mercury
using VSOP87 theory. Provides longitude, latitude, radius, speed,
and declination functions.

Author BlueprintResearch (Javonnii)
license MIT License - Free to use with attribution

theory VSOP87A (Heliocentric rectangular coordinates)
ACCURACY Truncated series (~10-15 terms per series) - arcsecond precision
@time_scale Julian millennia from J2000.0 (use core.get_julian_millennia)

reference Meeus, Jean. "Astronomical Algorithms" (2nd Ed., 1998)
Bretagnon & Francou. "VSOP87 Solutions" (1988)

showcase Includes commented showcase code with 250-bar future projection.
Uncomment to display Mercury data with polyline projections.

@open_source This library is part of an open-source alternative to
proprietary astronomical libraries. Study, modify, and
share freely. We believe knowledge of the cosmos belongs
to everyone.

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© 2025 BlueprintResearch / Javonnii
Licensed under MIT License
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version=6
import BlueprintResearch/lib_vsop_core/1 as core

get_helio_lon(t)
  Computes Mercury's heliocentric ecliptic longitude using VSOP87 theory.
  Parameters:
    t (float): (float) Julian millennia from J2000.0 (use core.get_julian_millennia(time)).
  Returns: (float) Heliocentric ecliptic longitude in degrees, normalized to range [0, 360).

get_helio_lat(t)
  Computes Mercury's heliocentric ecliptic latitude using VSOP87 theory.
  Parameters:
    t (float): (float) Julian millennia from J2000.0 (use core.get_julian_millennia(time)).
  Returns: (float) Heliocentric ecliptic latitude in radians, range approximately [-0.122, +0.122]. Note: Returns radians, not degrees.

get_helio_radius(t)
  Computes Mercury's heliocentric radius (distance from Sun) using VSOP87 theory.
  Parameters:
    t (float): (float) Julian millennia from J2000.0 (use core.get_julian_millennia(time)).
  Returns: (float) Heliocentric radius in astronomical units (AU). Typical range is 0.31-0.47 AU.

get_geo_speed(t)
  Computes Mercury's geocentric longitude speed (rate of change over time).
  Parameters:
    t (float): (float) Julian millennia from J2000.0 (use core.get_julian_millennia(time)).
  Returns: (float) Geocentric longitude speed in degrees per day. Negative values indicate retrograde motion (apparent backward movement).

get_geo_lon(t)
  Computes Mercury's geocentric ecliptic longitude (as seen from Earth).
  Parameters:
    t (float): (float) Julian millennia from J2000.0 (use core.get_julian_millennia(time)).
  Returns: (float) Geocentric ecliptic longitude in degrees, normalized to range [0, 360).

get_geo_ecl_lat(t)
  Computes Mercury's geocentric ecliptic latitude (as seen from Earth).
  Parameters:
    t (float): (float) Julian millennia from J2000.0 (use core.get_julian_millennia(time)).
  Returns: (float) Geocentric ecliptic latitude in degrees, range approximately [-7, +7].

get_geo_decl(t)
  Computes Mercury's geocentric equatorial declination (as seen from Earth).
  Parameters:
    t (float): (float) Julian millennia from J2000.0 (use core.get_julian_millennia(time)).
  Returns: (float) Geocentric equatorial declination in degrees, range [-90, +90] where positive is north.