astronomia
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An astronomical library
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JavaScript
;
Object.defineProperty(exports, '__esModule', { value: true });
var base = require('./base.cjs');
var coord = require('./coord.cjs');
var nutation = require('./nutation.cjs');
var planetposition = require('./planetposition.cjs');
/**
* @copyright 2013 Sonia Keys
* @copyright 2016 commenthol
* @license MIT
* @module saturnring
*/
/**
* Ring computes quantities of the ring of Saturn.
*
* B Saturnicentric latitude of the Earth referred to the plane of the ring.
* Bʹ Saturnicentric latitude of the Sun referred to the plane of the ring.
* ΔU Difference between Saturnicentric longitudes of the Sun and the Earth.
* P Geometric position angle of the northern semiminor axis of the ring.
* aEdge Major axis of the out edge of the outer ring.
* bEdge Minor axis of the out edge of the outer ring.
*
* All results in radians.
*/
function ring (jde, earth, saturn) { // (jde float64, earth, saturn *pp.V87Planet) (B, Bʹ, ΔU, P, aEdge, bEdge float64)
const [f1, f2] = cl(jde, earth, saturn);
const [ΔU, B] = f1();
const [Bʹ, P, aEdge, bEdge] = f2();
return [B, Bʹ, ΔU, P, aEdge, bEdge]
}
/**
* UB computes quantities required by illum.Saturn().
*
* Same as ΔU and B returned by Ring(). Results in radians.
*/
function ub (jde, earth, saturn) { // (jde float64, earth, saturn *pp.V87Planet) (ΔU, B float64)
const [f1, f2] = cl(jde, earth, saturn); // eslint-disable-line no-unused-vars
return f1()
}
/**
* cl splits the work into two closures.
*/
function cl (jde, earth, saturn) { // (jde float64, earth, saturn *pp.V87Planet) (f1 func() (ΔU, B float64),
// f2 func() (Bʹ, P, aEdge, bEdge float64))
const p = Math.PI / 180;
let i, Ω;
let l0, b0, R;
let Δ = 9.0;
let λ, β;
let si, ci, sβ, cβ, sB;
let sbʹ, cbʹ, slʹΩ, clʹΩ;
const f1 = function () { // (ΔU, B float64)
// (45.1), p. 318
const T = base["default"].J2000Century(jde);
i = base["default"].horner(T, 28.075216 * p, -0.012998 * p, 0.000004 * p);
Ω = base["default"].horner(T, 169.50847 * p, 1.394681 * p, 0.000412 * p);
// Step 2.0
const earthPos = earth.position(jde);
R = earthPos.range;
const fk5 = planetposition["default"].toFK5(earthPos.lon, earthPos.lat, jde);
l0 = fk5.lon;
b0 = fk5.lat;
const [sl0, cl0] = base["default"].sincos(l0);
const sb0 = Math.sin(b0);
// Steps 3, 4.0
let l = 0;
let b = 0;
let r = 0;
let x = 0;
let y = 0;
let z = 0;
const f = function () {
const τ = base["default"].lightTime(Δ);
const saturnPos = saturn.position(jde - τ);
r = saturnPos.range;
const fk5 = planetposition["default"].toFK5(saturnPos.lon, saturnPos.lat, jde);
l = fk5.lon;
b = fk5.lat;
const [sl, cl] = base["default"].sincos(l);
const [sb, cb] = base["default"].sincos(b);
x = r * cb * cl - R * cl0;
y = r * cb * sl - R * sl0;
z = r * sb - R * sb0;
Δ = Math.sqrt(x * x + y * y + z * z);
};
f();
f();
// Step 5.0
λ = Math.atan2(y, x);
β = Math.atan(z / Math.hypot(x, y));
// First part of step 6.0
si = Math.sin(i);
ci = Math.cos(i);
sβ = Math.sin(β);
cβ = Math.cos(β);
sB = si * cβ * Math.sin(λ - Ω) - ci * sβ;
const B = Math.asin(sB); // return value
// Step 7.0
const N = 113.6655 * p + 0.8771 * p * T;
const lʹ = l - 0.01759 * p / r;
const bʹ = b - 0.000764 * p * Math.cos(l - N) / r;
// Setup for steps 8, 9.0
sbʹ = Math.sin(bʹ);
cbʹ = Math.cos(bʹ);
slʹΩ = Math.sin(lʹ - Ω);
clʹΩ = Math.cos(lʹ - Ω);
// Step 9.0
const [sλΩ, cλΩ] = base["default"].sincos(λ - Ω);
const U1 = Math.atan2(si * sbʹ + ci * cbʹ * slʹΩ, cbʹ * clʹΩ);
const U2 = Math.atan2(si * sβ + ci * cβ * sλΩ, cβ * cλΩ);
const ΔU = Math.abs(U1 - U2); // return value
return [ΔU, B]
};
const f2 = function () { // (Bʹ, P, aEdge, bEdge) {
// Remainder of step 6.0
const aEdge = 375.35 / 3600 * p / Δ; // return value
const bEdge = aEdge * Math.abs(sB); // return value
// Step 8.0
const sBʹ = si * cbʹ * slʹΩ - ci * sbʹ;
const Bʹ = Math.asin(sBʹ); // return value
// Step 10.0
const [Δψ, Δε] = nutation["default"].nutation(jde);
const ε = nutation["default"].meanObliquity(jde) + Δε;
// Step 11.0
let λ0 = Ω - Math.PI / 2;
const β0 = Math.PI / 2 - i;
// Step 12.0
const [sl0λ, cl0λ] = base["default"].sincos(l0 - λ);
λ += 0.005693 * p * cl0λ / cβ;
β += 0.005693 * p * sl0λ * sβ;
// Step 13.0
λ0 += Δψ;
λ += Δψ;
// Step 14.0
let eq = new coord["default"].Ecliptic(λ0, β0).toEquatorial(ε);
const [α0, δ0] = [eq.ra, eq.dec];
eq = new coord["default"].Ecliptic(λ, β).toEquatorial(ε);
const [α, δ] = [eq.ra, eq.dec];
// Step 15.0
const [sδ0, cδ0] = base["default"].sincos(δ0);
const [sδ, cδ] = base["default"].sincos(δ);
const [sα0α, cα0α] = base["default"].sincos(α0 - α);
const P = Math.atan2(cδ0 * sα0α, sδ0 * cδ - cδ0 * sδ * cα0α); // return value
return [Bʹ, P, aEdge, bEdge]
};
return [f1, f2]
}
var saturnring = {
ring,
ub
};
exports["default"] = saturnring;
exports.ring = ring;
exports.ub = ub;