Example #1
0
// Position computes apparent position angle and angular distance of
// components of a binary star.
//
//	e is eccentricity of the true orbit
//	a is angular apparent semimajor axis
//	i is inclination relative to the line of sight
//	Ω is position angle of the ascending node
//	ω is longitude of periastron
//	E is eccentric anomaly, computed for example with package kepler
//	   and the mean anomaly as returned by function M in this package.
//
// Return value θ is the apparent position angle, ρ is the angular distance.
func Position(e float64, a, i, Ω, ω, E unit.Angle) (θ, ρ unit.Angle) {
	r := a.Mul(1 - e*E.Cos())
	ν := unit.Angle(2 * math.Atan(math.Sqrt((1+e)/(1-e))*E.Div(2).Tan()))
	sνω, cνω := (ν + ω).Sincos()
	ci := i.Cos()
	num := sνω * ci
	θ = (unit.Angle(math.Atan2(num, cνω)) + Ω).Mod1()
	ρ = r.Mul(math.Sqrt(num*num + cνω*cνω))
	return
}
Example #2
0
// Semidiameter returns semidiameter at specified distance.
//
// Δ must be observer-body distance in AU.
func Semidiameter(s0 unit.Angle, Δ float64) unit.Angle {
	return s0.Div(Δ)
}