func TestPrecessor_Precess(t *testing.T) {
// Exercise, p. 136.
eqFrom := &coord.Equatorial{
RA: base.NewRA(2, 31, 48.704).Rad(),
Dec: base.NewAngle(false, 89, 15, 50.72).Rad(),
}
mα := base.NewHourAngle(false, 0, 0, .19877)
mδ := base.NewAngle(false, 0, 0, -.0152)
epochs := []float64{
base.JDEToJulianYear(base.B1900),
2050,
2100,
}
answer := []string{
"α = 1ʰ22ᵐ33ˢ.90 δ = +88°46′26″.18",
"α = 3ʰ48ᵐ16ˢ.43 δ = +89°27′15″.38",
"α = 5ʰ53ᵐ29ˢ.17 δ = +89°32′22″.18",
}
eqTo := &coord.Equatorial{}
for i, epochTo := range epochs {
precess.Position(eqFrom, eqTo, 2000, epochTo, mα, mδ)
if answer[i] != fmt.Sprintf("α = %0.2d δ = %+0.2d",
base.NewFmtRA(eqTo.RA), base.NewFmtAngle(eqTo.Dec)) {
t.Fatal(i)
}
}
}
// Exercise, p. 136.
func TestPosition(t *testing.T) {
eqFrom := &coord.Equatorial{
base.NewRA(2, 31, 48.704).Rad(),
base.NewAngle(false, 89, 15, 50.72).Rad(),
}
eqTo := &coord.Equatorial{}
mα := base.NewHourAngle(false, 0, 0, 0.19877)
mδ := base.NewAngle(true, 0, 0, 0.0152)
for _, tc := range []struct {
α, δ string
jde float64
}{
{"1 22 33.90", "88 46 26.18", base.BesselianYearToJDE(1900)},
{"3 48 16.43", "89 27 15.38", base.JulianYearToJDE(2050)},
{"5 53 29.17", "89 32 22.18", base.JulianYearToJDE(2100)},
} {
epochTo := base.JDEToJulianYear(tc.jde)
precess.Position(eqFrom, eqTo, 2000.0, epochTo, mα, mδ)
αStr := fmt.Sprintf("%.2x", base.NewFmtRA(eqTo.RA))
δStr := fmt.Sprintf("%.2x", base.NewFmtAngle(eqTo.Dec))
if αStr != tc.α {
t.Fatal("got:", αStr, "want:", tc.α)
}
if δStr != tc.δ {
t.Fatal(δStr)
}
}
}
// Exercise, p. 136.
func TestPosition(t *testing.T) {
eqFrom := &coord.Equatorial{
unit.NewRA(2, 31, 48.704),
unit.NewAngle(' ', 89, 15, 50.72),
}
eqTo := &coord.Equatorial{}
mα := unit.HourAngleFromSec(0.19877)
mδ := unit.AngleFromSec(-0.0152)
for _, tc := range []struct {
α, δ string
jde float64
}{
{"1ʰ22ᵐ33.90ˢ", "88°46′26.18″", base.BesselianYearToJDE(1900)},
{"3ʰ48ᵐ16.43ˢ", "89°27′15.38″", base.JulianYearToJDE(2050)},
{"5ʰ53ᵐ29.17ˢ", "89°32′22.18″", base.JulianYearToJDE(2100)},
} {
epochTo := base.JDEToJulianYear(tc.jde)
precess.Position(eqFrom, eqTo, 2000.0, epochTo, mα, mδ)
αStr := fmt.Sprintf("%.2s", sexa.FmtRA(eqTo.RA))
δStr := fmt.Sprintf("%.2s", sexa.FmtAngle(eqTo.Dec))
if αStr != tc.α {
t.Fatal("got:", αStr, "want:", tc.α)
}
if δStr != tc.δ {
t.Fatal(δStr)
}
}
}
// Position computes the apparent position of an object.
//
// Position is computed for equatorial coordinates in eqFrom, considering
// proper motion, precession, nutation, and aberration. Result is in
// eqTo. EqFrom and eqTo must be non-nil, but may point to the same struct.
func Position(eqFrom, eqTo *coord.Equatorial, epochFrom, epochTo float64, mα sexa.HourAngle, mδ sexa.Angle) *coord.Equatorial {
precess.Position(eqFrom, eqTo, epochFrom, epochTo, mα, mδ)
jd := base.JulianYearToJDE(epochTo)
Δα1, Δδ1 := Nutation(eqTo.RA, eqTo.Dec, jd)
Δα2, Δδ2 := Aberration(eqTo.RA, eqTo.Dec, jd)
eqTo.RA += Δα1 + Δα2
eqTo.Dec += Δδ1 + Δδ2
return eqTo
}
// PositionRonVondrak computes the apparent position of an object using
// the Ron-Vondrák expression for aberration.
//
// Position is computed for equatorial coordinates in eqFrom, considering
// proper motion, aberration, precession, and nutation. Result is in
// eqTo. EqFrom and eqTo must be non-nil, but may point to the same struct.
//
// Note the Ron-Vondrák expression is only valid for the epoch J2000.
// EqFrom must be coordinates at epoch J2000.
func PositionRonVondrak(eqFrom, eqTo *coord.Equatorial, epochTo float64, mα sexa.HourAngle, mδ sexa.Angle) *coord.Equatorial {
t := epochTo - 2000
eqTo.RA = eqFrom.RA + mα.Rad()*t
eqTo.Dec = eqFrom.Dec + mδ.Rad()*t
jd := base.JulianYearToJDE(epochTo)
Δα, Δδ := AberrationRonVondrak(eqTo.RA, eqTo.Dec, jd)
eqTo.RA += Δα
eqTo.Dec += Δδ
precess.Position(eqTo, eqTo, 2000, epochTo, 0, 0)
Δα1, Δδ1 := Nutation(eqTo.RA, eqTo.Dec, jd)
eqTo.RA += Δα1
eqTo.Dec += Δδ1
return eqTo
}
// PositionRonVondrak computes the apparent position of an object using
// the Ron-Vondrák expression for aberration.
//
// Position is computed for equatorial coordinates in eqFrom, considering
// proper motion, aberration, precession, and nutation. Result is in
// eqTo. EqFrom and eqTo must be non-nil, but may point to the same struct.
//
// Note the Ron-Vondrák expression is only valid for the epoch J2000.
// EqFrom must be coordinates at epoch J2000.
func PositionRonVondrak(eqFrom, eqTo *coord.Equatorial, epochTo float64, mα unit.HourAngle, mδ unit.Angle) *coord.Equatorial {
t := epochTo - 2000
eqTo.RA = eqFrom.RA.Add(mα.Mul(t))
eqTo.Dec = eqFrom.Dec + mδ.Mul(t)
jd := base.JulianYearToJDE(epochTo)
Δα, Δδ := AberrationRonVondrak(eqTo.RA, eqTo.Dec, jd)
eqTo.RA = eqTo.RA.Add(Δα)
eqTo.Dec += Δδ
precess.Position(eqTo, eqTo, 2000, epochTo, 0, 0)
Δα1, Δδ1 := Nutation(eqTo.RA, eqTo.Dec, jd)
eqTo.RA = eqTo.RA.Add(Δα1)
eqTo.Dec += Δδ1
return eqTo
}
func ExamplePosition() {
// Example 21.b, p. 135.
eq := &coord.Equatorial{
base.NewRA(2, 44, 11.986).Rad(),
base.NewAngle(false, 49, 13, 42.48).Rad(),
}
epochFrom := 2000.0
jdTo := julian.CalendarGregorianToJD(2028, 11, 13.19)
epochTo := base.JDEToJulianYear(jdTo)
precess.Position(eq, eq, epochFrom, epochTo,
base.NewHourAngle(false, 0, 0, 0.03425),
base.NewAngle(true, 0, 0, 0.0895))
fmt.Printf("%0.3d\n", base.NewFmtRA(eq.RA))
fmt.Printf("%+0.2d\n", base.NewFmtAngle(eq.Dec))
// Output:
// 2ʰ46ᵐ11ˢ.331
// +49°20′54″.54
}