// Times computes UT rise, transit and set times for a celestial object on
// a day of interest.
//
// The function argurments do not actually include the day, but do include
// a number of values computed from the day.
//
// p is geographic coordinates of observer.
// ΔT is delta T.
// h0 is "standard altitude" of the body.
// Th0 is apparent sidereal time at 0h UT at Greenwich.
// α3, δ3 are slices of three right ascensions and declinations.
//
// h0 unit is radians.
//
// Th0 must be the time on the day of interest, in seconds.
// See sidereal.Apparent0UT.
//
// α3, δ3 must be values at 0h dynamical time for the day before, the day of,
// and the day after the day of interest. Units are radians.
//
// Result units are seconds of day and are in the range [0,86400).
func Times(p globe.Coord, ΔT unit.Time, h0 unit.Angle, Th0 unit.Time, α3 []unit.RA, δ3 []unit.Angle) (tRise, tTransit, tSet unit.Time, err error) {
tRise, tTransit, tSet, err = ApproxTimes(p, h0, Th0, α3[1], δ3[1])
if err != nil {
return
}
αf := make([]float64, 3)
for i, α := range α3 {
αf[i] = α.Rad()
}
δf := make([]float64, 3)
for i, δ := range δ3 {
δf[i] = δ.Rad()
}
var d3α, d3δ *interp.Len3
d3α, err = interp.NewLen3(-86400, 86400, αf)
if err != nil {
return
}
d3δ, err = interp.NewLen3(-86400, 86400, δf)
if err != nil {
return
}
// adjust tTransit
{
th0 := (Th0 + tTransit.Mul(360.985647/360)).Mod1()
α := d3α.InterpolateX((tTransit + ΔT).Sec())
// local hour angle as Time
H := th0 - unit.TimeFromRad(p.Lon.Rad()+α)
tTransit -= H
}
// adjust tRise, tSet
sLat, cLat := p.Lat.Sincos()
adjustRS := func(m unit.Time) (unit.Time, error) {
th0 := (Th0 + m.Mul(360.985647/360)).Mod1()
ut := (m + ΔT).Sec()
α := d3α.InterpolateX(ut)
δ := d3δ.InterpolateX(ut)
Hrad := th0.Rad() - p.Lon.Rad() - α
sδ, cδ := math.Sincos(δ)
sH, cH := math.Sincos(Hrad)
h := math.Asin(sLat*sδ + cLat*cδ*cH)
md := (unit.TimeFromRad(h) - h0.Time()).Div(cδ * cLat * sH)
return m + md, nil
}
tRise, err = adjustRS(tRise)
if err != nil {
return
}
tSet, err = adjustRS(tSet)
return
}
// MinSepRect returns the minimum separation between two moving objects.
//
// Like MinSep, but using a method of rectangular coordinates that gives
// accurate results even for close approaches.
func MinSepRect(jd1, jd3 float64, r1, d1, r2, d2 []float64) (float64, error) {
if len(r1) != 3 || len(d1) != 3 || len(r2) != 3 || len(d2) != 3 {
return 0, interp.ErrorNot3
}
uv := func(r1, d1, r2, d2 float64) (u, v float64) {
sd1, cd1 := math.Sincos(d1)
Δr := r2 - r1
tΔr := math.Tan(Δr)
thΔr := math.Tan(Δr / 2)
K := 1 / (1 + sd1*sd1*tΔr*thΔr)
sΔd := math.Sin(d2 - d1)
u = -K * (1 - (sd1/cd1)*sΔd) * cd1 * tΔr
v = K * (sΔd + sd1*cd1*tΔr*thΔr)
return
}
us := make([]float64, 3, 6)
vs := us[3:6]
for x, r := range r1 {
us[x], vs[x] = uv(r, d1[x], r2[x], d2[x])
}
u3, err := interp.NewLen3(-1, 1, us)
if err != nil {
panic(err) // bug not caller's fault.
}
v3, err := interp.NewLen3(-1, 1, vs)
if err != nil {
panic(err) // bug not caller's fault.
}
up0 := (us[2] - us[0]) / 2
vp0 := (vs[2] - vs[0]) / 2
up1 := us[0] + us[2] - 2*us[1]
vp1 := vs[0] + vs[2] - 2*vs[1]
up := up0
vp := vp0
dn := -(us[1]*up + vs[1]*vp) / (up*up + vp*vp)
n := dn
var u, v float64
for limit := 0; limit < 10; limit++ {
u = u3.InterpolateN(n)
v = v3.InterpolateN(n)
if math.Abs(dn) < 1e-5 {
return math.Hypot(u, v), nil // success
}
up := up0 + n*up1
vp := vp0 + n*vp1
dn = -(u*up + v*vp) / (up*up + vp*vp)
n += dn
}
return 0, errors.New("MinSepRect: failure to converge")
}
func ExampleLen3_Zero() {
// Example 3.c, p. 26.
x1 := 26.
x3 := 28.
// the y unit doesn't matter. working in degrees is fine
yTable := []float64{
base.DMSToDeg(true, 0, 28, 13.4),
base.DMSToDeg(false, 0, 6, 46.3),
base.DMSToDeg(false, 0, 38, 23.2),
}
d3, err := interp.NewLen3(x1, x3, yTable)
if err != nil {
fmt.Println(err)
return
}
x, err := d3.Zero(false)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("February %.5f\n", x)
i, frac := math.Modf(x)
fmt.Printf("February %d, at %.62s TD",
int(i), base.NewFmtTime(frac*24*3600))
// Output:
// February 26.79873
// February 26, at 19ʰ10ᵐ TD
}
func ExampleLen3_Zero() {
// Example 3.c, p. 26.
x1 := 26.
x3 := 28.
// the y unit doesn't matter. working in degrees is fine
yTable := []float64{
unit.FromSexa('-', 0, 28, 13.4),
unit.FromSexa(' ', 0, 6, 46.3),
unit.FromSexa(' ', 0, 38, 23.2),
}
d3, err := interp.NewLen3(x1, x3, yTable)
if err != nil {
fmt.Println(err)
return
}
x, err := d3.Zero(false)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("February %.5f\n", x)
i, frac := math.Modf(x)
fmt.Printf("February %d, at %m TD",
int(i), sexa.FmtTime(unit.TimeFromDay(frac)))
// Output:
// February 26.79873
// February 26, at 19ʰ10ᵐ TD
}
func ExampleLen3_Extremum() {
// Example 3.b, p. 26.
d3, err := interp.NewLen3(12, 20, []float64{
1.3814294,
1.3812213,
1.3812453,
})
if err != nil {
fmt.Println(err)
return
}
x, y, err := d3.Extremum()
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("distance: %.7f AU\n", y)
fmt.Printf("date: %.4f\n", x)
i, frac := math.Modf(x)
fmt.Printf("1992 May %d, at %.64s TD",
int(i), base.NewFmtTime(frac*24*3600))
// Output:
// distance: 1.3812030 AU
// date: 17.5864
// 1992 May 17, at 14ʰ TD
}
// Times computes UT rise, transit and set times for a celestial object on
// a day of interest.
//
// The function argurments do not actually include the day, but do include
// a number of values computed from the day.
//
// p is geographic coordinates of observer.
// ΔT is delta T.
// h0 is "standard altitude" of the body.
// Th0 is apparent sidereal time at 0h UT at Greenwich.
// α3, δ3 are slices of three right ascensions and declinations.
//
// ΔT unit is seconds. See package deltat.
//
// h0 unit is radians.
//
// Th0 must be the time on the day of interest, in seconds.
// See sidereal.Apparent0UT.
//
// α3, δ3 must be values at 0h dynamical time for the day before, the day of,
// and the day after the day of interest. Units are radians.
//
// Result units are seconds and are in the range [0,86400)
func Times(p globe.Coord, ΔT, h0, Th0 float64, α3, δ3 []float64) (mRise, mTransit, mSet float64, err error) {
mRise, mTransit, mSet, err = ApproxTimes(p, h0, Th0, α3[1], δ3[1])
if err != nil {
return
}
var d3α, d3δ *interp.Len3
d3α, err = interp.NewLen3(-86400, 86400, α3)
if err != nil {
return
}
d3δ, err = interp.NewLen3(-86400, 86400, δ3)
if err != nil {
return
}
// adjust mTransit
{
th0 := base.PMod(Th0+mTransit*360.985647/360, 86400)
α := d3α.InterpolateX(mTransit + ΔT)
H := th0 - (p.Lon+α)*43200/math.Pi
mTransit -= H
}
// adjust mRise, mSet
sLat, cLat := math.Sincos(p.Lat)
adjustRS := func(m float64) (float64, error) {
th0 := base.PMod(Th0+m*360.985647/360, 86400)
ut := m + ΔT
α := d3α.InterpolateX(ut)
δ := d3δ.InterpolateX(ut)
H := th0 - (p.Lon+α)*43200/math.Pi
sδ, cδ := math.Sincos(δ)
h := sLat*sδ + cLat*cδ*math.Cos(H)
return m + (h-h0)/cδ*cLat*math.Sin(H), nil
}
mRise, err = adjustRS(mRise)
if err != nil {
return
}
mSet, err = adjustRS(mSet)
return
}
func ap2a(j1, d float64, a bool, v *pp.V87Planet) (jde, r float64) {
// Meeus doesn't give a complete algorithm for finding accurate answers.
// The algorithm here starts with the approximate result algorithm
// then crawls along the curve at resultion d until three points
// are found containing the desired extremum. It's slow if the starting
// point is far away (the case of Neptune) or if high accuracy is
// demanded. 1 day accuracy is generally quick.
j0 := j1 - d
j2 := j1 + d
rr := make([]float64, 3)
_, _, rr[0] = v.Position2000(j0)
_, _, rr[1] = v.Position2000(j1)
_, _, rr[2] = v.Position2000(j2)
for {
if a {
if rr[1] > rr[0] && rr[1] > rr[2] {
break
}
} else {
if rr[1] < rr[0] && rr[1] < rr[2] {
break
}
}
if rr[0] < rr[2] == a {
j0 = j1
j1 = j2
j2 += d
rr[0] = rr[1]
rr[1] = rr[2]
_, _, rr[2] = v.Position2000(j2)
} else {
j2 = j1
j1 = j0
j0 -= d
rr[2] = rr[1]
rr[1] = rr[0]
_, _, rr[0] = v.Position2000(j0)
}
}
l, err := interp.NewLen3(j0, j2, rr)
if err != nil {
panic(err) // unexpected.
}
jde, r, err = l.Extremum()
if err != nil {
panic(err) // unexpected.
}
return
}
// MinSep returns the minimum separation between two moving objects.
//
// The motion is represented as an ephemeris of three rows, equally spaced
// in time. Jd1, jd3 are julian day times of the first and last rows.
// R1, d1, r2, d2 are coordinates at the three times. They must each be
// slices of length 3.
//
// Result is obtained by computing separation at each of the three times
// and interpolating a minimum. This may be invalid for sufficiently close
// approaches.
func MinSep(jd1, jd3 float64, r1, d1, r2, d2 []float64) (float64, error) {
if len(r1) != 3 || len(d1) != 3 || len(r2) != 3 || len(d2) != 3 {
return 0, interp.ErrorNot3
}
y := make([]float64, 3)
for x, r := range r1 {
y[x] = Sep(r, d1[x], r2[x], d2[x])
}
d3, err := interp.NewLen3(jd1, jd3, y)
if err != nil {
return 0, err
}
_, dMin, err := d3.Extremum()
return dMin, err
}
func ExampleLen3_InterpolateX() {
// Example 3.a, p. 25.
d3, err := interp.NewLen3(7, 9, []float64{
.884226,
.877366,
.870531,
})
if err != nil {
fmt.Println(err)
return
}
x := 8 + base.NewTime(false, 4, 21, 0).Day() // 8th day at 4:21
y := d3.InterpolateX(x)
fmt.Printf("%.6f\n", y)
// Output:
// 0.876125
}
func ExampleLen5_Zero() {
// Exercise, p. 30.
x1 := 25.
x5 := 29.
yTable := []float64{
base.DMSToDeg(true, 1, 11, 21.23),
base.DMSToDeg(true, 0, 28, 12.31),
base.DMSToDeg(false, 0, 16, 07.02),
base.DMSToDeg(false, 1, 01, 00.13),
base.DMSToDeg(false, 1, 45, 46.33),
}
d5, err := interp.NewLen5(x1, x5, yTable)
if err != nil {
fmt.Println(err)
return
}
z, err := d5.Zero(false)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("1988 January %.6f\n", z)
zInt, zFrac := math.Modf(z)
fmt.Printf("1988 January %d at %.62s TD\n", int(zInt),
base.NewFmtTime(zFrac*24*3600))
// compare result to that from just three central values
d3, err := interp.NewLen3(26, 28, yTable[1:4])
if err != nil {
fmt.Println(err)
return
}
z3, err := d3.Zero(false)
if err != nil {
fmt.Println(err)
return
}
dz := z - z3
fmt.Printf("%.6f day\n", dz)
fmt.Printf("%.1f minute\n", dz*24*60)
// Output:
// 1988 January 26.638587
// 1988 January 26 at 15ʰ20ᵐ TD
// 0.000753 day
// 1.1 minute
}
func ExampleLen3_InterpolateN() {
// Example 3.a, p. 25.
d3, err := interp.NewLen3(7, 9, []float64{
.884226,
.877366,
.870531,
})
if err != nil {
fmt.Println(err)
return
}
n := 4.35 / 24
y := d3.InterpolateN(n)
fmt.Printf("%.6f\n", y)
// Output:
// 0.876125
}
func ExampleLen3_Zero_strong() {
// Example 3.d, p. 27.
x1 := -1.
x3 := 1.
yTable := []float64{-2, 3, 2}
d3, err := interp.NewLen3(x1, x3, yTable)
if err != nil {
fmt.Println(err)
return
}
x, err := d3.Zero(true)
if err != nil {
fmt.Println(err)
return
}
fmt.Printf("%.12f\n", x)
// Output:
// -0.720759220056
}
func ap2a(j1, d float64, a bool, v *pp.V87Planet) (jde, r float64) {
j0 := j1 - d
j2 := j1 + d
rr := make([]float64, 3)
_, _, rr[0] = v.Position2000(j0)
_, _, rr[1] = v.Position2000(j1)
_, _, rr[2] = v.Position2000(j2)
for {
if a {
if rr[1] > rr[0] && rr[1] > rr[2] {
break
}
} else {
if rr[1] < rr[0] && rr[1] < rr[2] {
break
}
}
if rr[0] < rr[2] == a {
j0 = j1
j1 = j2
j2 += d
rr[0] = rr[1]
rr[1] = rr[2]
_, _, rr[2] = v.Position2000(j2)
} else {
j2 = j1
j1 = j0
j0 -= d
rr[2] = rr[1]
rr[1] = rr[0]
_, _, rr[0] = v.Position2000(j0)
}
}
l, err := interp.NewLen3(j0, j2, rr)
if err != nil {
panic(err) // unexpected.
}
jde, r, err = l.Extremum()
if err != nil {
panic(err) // unexpected.
}
return
}
func ExampleLen3_InterpolateN() {
// Example 3.a, p. 25.
d3, err := interp.NewLen3(7, 9, []float64{
.884226,
.877366,
.870531,
})
if err != nil {
fmt.Println(err)
return
}
h := unit.FromSexa(0, 4, 21, 0)
fmt.Println(h, "hours")
n := h / 24
y := d3.InterpolateN(n)
fmt.Printf("%.6f\n", y)
// Output:
// 4.35 hours
// 0.876125
}