constants.base

constants.base

Foundation classes for planetarypy.constants.

Three types live here:

:class:Constant — a thin astropy.units.Quantity subclass that carries provenance metadata (PCK source, IAU edition, body name, description, reference). Used for every value that comes directly out of a PCK kernel.
:class:Body — a frozen container of constants for one celestial body (Sun, planet, moon, asteroid, comet). Generated by the regenerator script, never hand-edited.
:class:BodyRegistry — a dict of bodies keyed by NAIF ID, with case-insensitive name lookup and class-based filtering helpers.

See docs/explanation/constants_design.qmd for the design rationale.

Classes

Name	Description
Body	All constants for one celestial body.
BodyRegistry	Dict of bodies keyed by NAIF ID, with name + class-based lookup.
Constant	A `Quantity` with attached PCK provenance metadata.

Body

constants.base.Body(
    name,
    naif_id,
    body_class,
    parent=None,
    dwarf_planet=False,
    mission_visited=False,
    radii=None,
    GM=None,
    long_axis=None,
    pole_ra=None,
    pole_dec=None,
    pm=None,
    rotation_rate=None,
    pole_ra_coeffs=None,
    pole_dec_coeffs=None,
    pm_coeffs=None,
    mean_radius=None,
    volume_radius=None,
    flattening=None,
    equatorial_radius=None,
    polar_radius=None,
    volumetric_mean_radius=None,
    core_radius=None,
    ellipticity=None,
    mean_density=None,
    surface_gravity=None,
    surface_acceleration=None,
    surface_acceleration_eq=None,
    surface_acceleration_pole=None,
    escape_velocity=None,
    bond_albedo=None,
    geometric_albedo=None,
    v_band_magnitude=None,
    solar_irradiance=None,
    black_body_temperature=None,
    topographic_range=None,
    moment_of_inertia=None,
    J2=None,
    number_of_satellites=None,
    has_ring_system=None,
    semimajor_axis=None,
    sidereal_orbit_period=None,
    tropical_orbit_period=None,
    perihelion=None,
    aphelion=None,
    synodic_period=None,
    mean_orbital_velocity=None,
    max_orbital_velocity=None,
    min_orbital_velocity=None,
    orbit_inclination=None,
    orbit_eccentricity=None,
    sidereal_rotation_period=None,
    length_of_day=None,
    obliquity_to_orbit=None,
    inclination_of_equator=None,
    surface_pressure=None,
    surface_density=None,
    scale_height=None,
    average_temperature=None,
    mean_molecular_weight=None,
    volume=None,
)

[source]

All constants for one celestial body.

Values that came directly from the PCK are :class:Constant instances (with provenance metadata); derived values (mass, density) are plain Quantity properties computed lazily from the PCK constants and astropy.constants.G.

Optional fields default to None — not every body in the PCK has every field (e.g. minor moons often have radii only).

Attributes

Name	Description
body_class	One of `"sun"`, `"planet"`, `"moon"`, `"asteroid"`, `"comet"`.
density	Mean density from `mass` over the triaxial ellipsoid volume.
dwarf_planet	`True` for IAU-classified dwarf planets (Pluto, Ceres, …).
mass	Body mass derived from `GM` and `astropy.constants.G`.
mission_visited	`True` for small bodies that have been flown by, orbited, or landed on.
naif_id	NAIF integer id (e.g. `499` for Mars).
name	Canonical PCK name (uppercase, e.g. `"MARS"`).
parent	NAIF id of parent planet for moons; `None` otherwise.

Methods

Name	Description
at_time	Return a snapshot Body with fields resolved as of `date`.
iter_constants	Yield `(field_name, Constant)` for every Constant-bearing field.

at_time

constants.base.Body.at_time(date)

Return a snapshot Body with fields resolved as of date.

Resolution rules:

PCK fields (radii, GM, pole_*, rotation_rate, …): pulled from whichever IAU PCK edition was current on date. IAU 2009 PCK published 2010-10-21; IAU 2015 PCK published 2018-09-20. Before 2010-10-21 no PCK existed → NSSDC fills in.
NSSDC-only fields (bond_albedo, surface_pressure, …): overlaid from NSSDC at the given date.

date accepts "2001" / "2001-06" / "2001-06-15" — year/year-month resolve to end-of-period.

Returns a fresh frozen Body; self is unmodified.

[source]

iter_constants

constants.base.Body.iter_constants()

Yield (field_name, Constant) for every Constant-bearing field.

Skips fields that are None (unset for this body) and fields whose value isn’t a :class:Constant — metadata like body_class / naif_id / dwarf_planet and structural tuples like pole_ra_coeffs or scalar floats like flattening are filtered out. The result is the set of per-body quantities with provenance.

Useful for tabular display, completions, and introspection without the caller needing to know the dataclass schema.

Example::

>>> from planetarypy.constants import Mars
>>> dict(Mars.iter_constants())["GM"]
<Constant Mars.GM = 42828.4 km3 / s2  (IAU 2015)>

[source]

BodyRegistry

constants.base.BodyRegistry(bodies=None)

[source]

Dict of bodies keyed by NAIF ID, with name + class-based lookup.

Indexable by either NAIF id (registry[499]) or name (registry["MARS"], registry["mars"] — case-insensitive).

Use :meth:by_class to filter by body_class and optional parent.

Methods

Name	Description
by_class	Filter by `body_class`, optionally also by `parent`.
find	Best-effort lookup by NAIF id or name; `None` on miss.

by_class

constants.base.BodyRegistry.by_class(body_class, parent=None)

Filter by body_class, optionally also by parent.

parent may be a NAIF id, a body name, or a :class:Body.

[source]

find

constants.base.BodyRegistry.find(query)

Best-effort lookup by NAIF id or name; None on miss.

[source]

Constant

constants.base.Constant()

[source]

A Quantity with attached PCK provenance metadata.

Behaves like any other :class:astropy.units.Quantity for math and unit operations — composes in formulas, supports .to(), slices, etc. View operations (slicing, copying, ufuncs) propagate metadata; explicitly demote to plain Quantity if you want a metadata-free value.

Metadata fields (all defaulting to empty/zero): name, body, description, reference, iau_year, source.