func ExamplePolyBefore948() {
// Example 10.b, p. 80.
ΔT := deltat.PolyBefore948(333.1)
UT := unit.TimeFromHour(6)
TD := UT + ΔT
fmt.Printf("%+.0f seconds\n", ΔT)
fmt.Printf("333 February 6 at %m TD", sexa.FmtTime(TD))
// Output:
// +6146 seconds
// 333 February 6 at 7ʰ42ᵐ TD
}
// Lunar computes quantities related to lunar eclipses.
//
// Argument year is a decimal year specifying a date.
//
// eclipseType will be None, Penumbral, Umbral, or Total.
// If None, none of the other return values may be meaningful.
//
// jmax is the jde when the center of the eclipse shadow is closest to the
// Moon center, in a plane through the center of the Moon.
//
// γ is the distance from the eclipse shadow center to the moon center
// at time jmax.
//
// σ is the radius of the umbral cone in the plane of the Moon.
//
// ρ is the radius of the penumbral cone.
//
// mag is eclipse magnitude.
//
// sd- return values are semidurations of the phases of the eclipse.
//
// γ, σ, and ρ are in units of equatorial Earth radii.
func Lunar(year float64) (eclipseType int, jmax, γ, ρ, σ, mag float64, sdTotal, sdPartial, sdPenumbral unit.Time) {
var e bool
var u, Mʹ float64
e, jmax, γ, u, Mʹ = g(snap(year, .5),
moonphase.MeanFull(year), -.4065, .1727)
if !e {
return // no eclipse
}
ρ = 1.2848 + u
σ = .7403 - u
aγ := math.Abs(γ)
mag = (1.0128 - u - aγ) / .545 // (54.3) p. 382
switch {
case mag > 1:
eclipseType = Total
case mag > 0:
eclipseType = Umbral
default:
mag = (1.5573 + u - aγ) / .545 // (54.4) p. 382
if mag < 0 {
return // no eclipse
}
eclipseType = Penumbral
}
p := 1.0128 - u
t := .4678 - u
n := .5458 + .04*math.Cos(Mʹ)
γ2 := γ * γ
switch eclipseType {
case Total:
sdTotal = unit.TimeFromHour(math.Sqrt(t*t-γ2) / n)
fallthrough
case Umbral:
sdPartial = unit.TimeFromHour(math.Sqrt(p*p-γ2) / n)
fallthrough
default:
h := 1.5573 + u
sdPenumbral = unit.TimeFromHour(math.Sqrt(h*h-γ2) / n)
}
return
}
func ExampleEclipticAtHorizon() {
ε := unit.AngleFromDeg(23.44)
φ := unit.AngleFromDeg(51)
θ := unit.TimeFromHour(5)
λ1, λ2, I := parallactic.EclipticAtHorizon(ε, φ, θ)
fmt.Println(sexa.FmtAngle(λ1))
fmt.Println(sexa.FmtAngle(λ2))
fmt.Println(sexa.FmtAngle(I))
// Output:
// 169°21′30″
// 349°21′30″
// 61°53′14″
}
