// AstrometricJ2000 is a utility function for computing astrometric coordinates.
//
// It is used internally and only exported so that it can be used from
// multiple packages. It is not otherwise expected to be used.
//
// Argument f is a function that returns J2000 equatorial rectangular
// coodinates of a body.
//
// Results are J2000 right ascention, declination, and elongation.
func AstrometricJ2000(f func(float64) (x, y, z float64), jde float64, e *pp.V87Planet) (α, δ, ψ float64) {
X, Y, Z := solarxyz.PositionJ2000(e, jde)
x, y, z := f(jde)
// (33.10) p. 229
ξ := X + x
η := Y + y
ζ := Z + z
Δ := math.Sqrt(ξ*ξ + η*η + ζ*ζ)
{
τ := base.LightTime(Δ)
x, y, z = f(jde - τ)
ξ = X + x
η = Y + y
ζ = Z + z
Δ = math.Sqrt(ξ*ξ + η*η + ζ*ζ)
}
α = math.Atan2(η, ξ)
if α < 0 {
α += 2 * math.Pi
}
δ = math.Asin(ζ / Δ)
R0 := math.Sqrt(X*X + Y*Y + Z*Z)
ψ = math.Acos((ξ*X + η*Y + ζ*Z) / R0 / Δ)
return
}
func ExamplePositionJ2000() {
// Example 26.b, p. 175 but for output see complete VSOP87
// results given on p. 176.
e, err := pp.LoadPlanet(pp.Earth)
if err != nil {
fmt.Println(err)
return
}
x, y, z := solarxyz.PositionJ2000(e, 2448908.5)
fmt.Printf("X0 = %.8f\n", x)
fmt.Printf("Y0 = %.8f\n", y)
fmt.Printf("Z0 = %.8f\n", z)
// Output:
// X0 = -0.93739707
// Y0 = -0.31316724
// Z0 = -0.13577841
}
// AstrometricJ2000 is a utility function for computing astrometric coordinates.
//
// It is used internally and only exported so that it can be used from
// multiple packages. It is not otherwise expected to be used.
//
// Argument f is a function that returns J2000 equatorial rectangular
// coodinates of a body.
//
// Results are J2000 right ascention, declination, and elongation.
func AstrometricJ2000(f func(float64) (x, y, z float64), jde float64, e *pp.V87Planet) (α unit.RA, δ, ψ unit.Angle) {
X, Y, Z := solarxyz.PositionJ2000(e, jde)
x, y, z := f(jde)
// (33.10) p. 229
ξ := X + x
η := Y + y
ζ := Z + z
Δ := math.Sqrt(ξ*ξ + η*η + ζ*ζ)
{
τ := base.LightTime(Δ)
x, y, z = f(jde - τ)
ξ = X + x
η = Y + y
ζ = Z + z
Δ = math.Sqrt(ξ*ξ + η*η + ζ*ζ)
}
α = unit.RAFromRad(math.Atan2(η, ξ))
δ = unit.Angle(math.Asin(ζ / Δ))
R0 := math.Sqrt(X*X + Y*Y + Z*Z)
ψ = unit.Angle(math.Acos((ξ*X + η*Y + ζ*Z) / R0 / Δ))
return
}