Astronomical Angles

The AstronomicAngle class encapsulates the slowly-varying astronomical arguments that drive the tidal potential: the mean longitudes and anomalies of the Moon and Sun, the longitude of the lunar node, and derived quantities such as the Doodson variables.

These angles are computed internally for every call to evaluate_tide() or evaluate_tide_from_constituents(), but the class is also exposed publicly so that users can inspect or reuse the values for nodal corrections and harmonic analysis.

class pyfes.AstronomicAngle

The AstronomicAngle class computes and stores the astronomical angles needed for tidal prediction and harmonic analysis. This include the six fundamental variables of the harmonic development as well as auxiliary angles derived from the lunar node longitude \(N\), which are required for nodal corrections.

property h

Mean longitude of the Sun, in radians (~0.99°/day)

property i

Obliquity of the lunar orbit to the celestial equator (\(I\)), in radians. Varies between ~18.3° and ~28.6° over the nodal cycle.

property n

Longitude of the Moon’s ascending node, in radians (~0.053°/day, 18.61-year cycle)

property nu

Right ascension of the lunar intersection (\(\nu\)), in radians.

property nuprim

Correction angle for \(K_1\) (\(\nu'\)), in radians. Combines lunar and solar diurnal contributions.

property nusec

Correction angle for \(K_2\) (\(\nu''\)), in radians. Combines lunar and solar semidiurnal contributions.

property p

Longitude of the lunar perigee, in radians (~0.11°/day, 8.85-year cycle)

property p1

Longitude of the solar perihelion, in radians (~0.00005°/day, ~20,940-year cycle)

property r

Phase factor for constituent \(L_2\) (\(R\)), in radians. Schureman formula 196.

property s

Mean longitude of the Moon, in radians (~13.18°/day).

property t

Mean solar angle relative to Greenwich (hour angle of the mean Sun), in radians

update(self: pyfes.core.AstronomicAngle, date: object) → None

Update the astronomic angles.

Parameters:

date – Desired UTC time

property x1ra

Amplitude factor for constituent \(L_2\) (\(1/P_a\)), dimensionless. Schureman formula 213.

property xi

Longitude in the Moon’s orbit of the lunar intersection (\(\xi\)), in radians.