func ExampleHorizontal() {
// Example 40.a, p. 280
π := parallax.Horizontal(.37276)
fmt.Printf("%.3s", sexa.FmtAngle(π))
// Output:
// 23.592″
}
func ExampleHorizontal() {
// Example 40.a, p. 280
π := parallax.Horizontal(.37276)
fmt.Printf("%.3f\n", π*180/math.Pi*60*60)
// Output:
// 23.592
}
func TestHorizontal(t *testing.T) {
// example from moonposition.Parallax, ch 47, p. 342
_, _, Δ := moonposition.Position(julian.CalendarGregorianToJD(1992, 4, 12))
π := parallax.Horizontal(Δ / base.AU).Deg()
want := .99199
// we don't quite get all the digits here.
// for close objects we need that Arcsin that's in moonposition.Parallax.
if math.Abs(π-want) > .0001 {
t.Fatal("got", π, "want", want)
}
}
// MoonTopocentric returns observed topocentric semidiameter of the Moon.
//
// Δ is distance to Moon in AU.
// δ is declination of Moon in radians.
// H is hour angle of Moon in radians.
// ρsφʹ, ρcφʹ are parallax constants as returned by
// globe.Ellipsoid.ParallaxConstants, for example.
//
// Result is semidiameter in radians.
func MoonTopocentric(Δ, δ, H, ρsφʹ, ρcφʹ float64) float64 {
const k = .272481
sπ := math.Sin(parallax.Horizontal(Δ))
// q computed by (40.6, 40.7) p. 280, ch 40.
sδ, cδ := math.Sincos(δ)
sH, cH := math.Sincos(H)
A := cδ * sH
B := cδ*cH - ρcφʹ*sπ
C := sδ - ρsφʹ*sπ
q := math.Sqrt(A*A + B*B + C*C)
return k / q * sπ
}
// MoonTopocentric returns observed topocentric semidiameter of the Moon.
//
// Δ is distance to Moon in AU.
// δ is declination of Moon.
// H is hour angle of Moon.
// ρsφʹ, ρcφʹ are parallax constants as returned by
// globe.Ellipsoid.ParallaxConstants, for example.
func MoonTopocentric(Δ float64, δ unit.Angle, H unit.HourAngle, ρsφʹ, ρcφʹ float64) float64 {
const k = .272481
sπ := parallax.Horizontal(Δ).Sin()
// q computed by (40.6, 40.7) p. 280, ch 40.
sδ, cδ := δ.Sincos()
sH, cH := H.Sincos()
A := cδ * sH
B := cδ*cH - ρcφʹ*sπ
C := sδ - ρsφʹ*sπ
q := math.Sqrt(A*A + B*B + C*C)
return k / q * sπ
}
// MoonTopocentric2 returns observed topocentric semidiameter of the Moon
// by a less rigorous method.
//
// Δ is distance to Moon in AU, h is altitude of the Moon above the observer's
// horizon in radians.
//
// Result is semidiameter in radians.
func MoonTopocentric2(Δ, h float64) float64 {
return Moon / Δ * (1 + math.Sin(h)*math.Sin(parallax.Horizontal(Δ)))
}
// MoonTopocentric2 returns observed topocentric semidiameter of the Moon
// by a less rigorous method.
//
// Δ is distance to Moon in AU, h is altitude of the Moon above the observer's
// horizon.
func MoonTopocentric2(Δ float64, h unit.Angle) unit.Angle {
return Moon.Mul((1 + h.Sin()*parallax.Horizontal(Δ).Sin()) / Δ)
}