// Solar computes quantities related to solar eclipses.
//
// Argument year is a decimal year specifying a date.
//
// eclipseType will be None, Partial, Annular, AnnularTotal, or Total.
// If None, none of the other return values may be meaningful.
//
// central is true if the center of the eclipse shadow touches the Earth.
//
// jmax is the jde when the center of the eclipse shadow is closest to the
// Earth center, in a plane through the center of the Earth.
//
// γ is the distance from the eclipse shadow center to the Earth center
// at time jmax.
//
// u is the radius of the Moon's umbral cone in the plane of the Earth.
//
// p is the radius of the penumbral cone.
//
// mag is eclipse magnitude for partial eclipses. It is not valid for other
// eclipse types.
//
// γ, u, and p are in units of equatorial Earth radii.
func Solar(year float64) (eclipseType int, central bool, jmax, γ, u, p, mag float64) {
var e bool
e, jmax, γ, u, _ = g(snap(year, 0), moonphase.MeanNew(year), -.4075, .1721)
p = u + .5461
if !e {
return // no eclipse
}
aγ := math.Abs(γ)
if aγ > 1.5433+u {
return // no eclipse
}
central = aγ < .9972 // eclipse center touches Earth
switch {
case !central:
eclipseType = Partial // most common case
if aγ < 1.026 { // umbral cone may touch earth
if aγ < .9972+math.Abs(u) { // total or annular
eclipseType = Total // report total in both cases
}
}
case u < 0:
eclipseType = Total
case u > .0047:
eclipseType = Annular
default:
ω := .00464 * math.Sqrt(1-γ*γ)
if u < ω {
eclipseType = AnnularTotal
} else {
eclipseType = Annular
}
}
if eclipseType == Partial {
// (54.2) p. 382
mag = (1.5433 + u - aγ) / (.5461 + 2*u)
}
return
}
func ExampleMeanNew() {
// Example 49.a, p. 353.
fmt.Printf("JDE = %.5f\n", moonphase.MeanNew(1977.13))
// Output:
// JDE = 2443192.94102
}