moonillum

Documentation

Overview

Moonillum: Chapter 48, Illuminated Fraction of the Moon's Disk

Also see functions Illuminated and Limb in package base. The function for computing illuminated fraction given a phase angle (48.1) is base.Illuminated. Formula (48.5) is implemented as base.Limb.

Index

• func PhaseAngle3(jde float64) unit.Angle
• func PhaseAngleEcl(λ, β unit.Angle, Δ float64, λ0 unit.Angle, R float64) unit.Angle
• func PhaseAngleEcl2(λ, β, λ0 unit.Angle) unit.Angle
• func PhaseAngleEq(α unit.RA, δ unit.Angle, Δ float64, α0 unit.RA, δ0 unit.Angle, R float64) unit.Angle
• func PhaseAngleEq2(α unit.RA, δ unit.Angle, α0 unit.RA, δ0 unit.Angle) unit.Angle

Examples

• PhaseAngle3
• PhaseAngleEq
• PhaseAngleEq2

Functions

func PhaseAngle3

func PhaseAngle3(jde float64) unit.Angle

PhaseAngle3 computes the phase angle of the Moon given a julian day.

Less accurate than PhaseAngle functions taking coordinates.

Example

package main

import (
	"fmt"

	"github.com/mooncaker816/learnmeeus/v3/base"
	"github.com/mooncaker816/learnmeeus/v3/julian"
	"github.com/mooncaker816/learnmeeus/v3/moonillum"
)

func main() {
	i := moonillum.PhaseAngle3(julian.CalendarGregorianToJD(1992, 4, 12))
	k := base.Illuminated(i)
	fmt.Printf("i = %.2f\n", i.Deg())
	fmt.Printf("k = %.4f\n", k)
}

Output:

i = 68.88
k = 0.6801

func PhaseAngleEcl

func PhaseAngleEcl(λ, β unit.Angle, Δ float64, λ0 unit.Angle, R float64) unit.Angle

PhaseAngleEcl computes the phase angle of the Moon given ecliptic coordinates.

Arguments λ, β, Δ are geocentric longitude, latitude, and distance to the Moon; λ0, R are longitude and distance to the Sun. Distances must be in the same units as each other.

func PhaseAngleEcl2

func PhaseAngleEcl2(λ, β, λ0 unit.Angle) unit.Angle

PhaseAngleEcl2 computes the phase angle of the Moon given ecliptic coordinates.

Less accurate than PhaseAngleEcl.

Arguments λ, β are geocentric longitude and latitude of the Moon; λ0 is longitude of the Sun.

func PhaseAngleEq

func PhaseAngleEq(α unit.RA, δ unit.Angle, Δ float64, α0 unit.RA, δ0 unit.Angle, R float64) unit.Angle

PhaseAngleEQ computes the phase angle of the Moon given equatorial coordinates.

Arguments α, δ, Δ are geocentric right ascension, declination, and distance to the Moon; α0, δ0, R are coordinates of the Sun. Angles must be in radians. Distances must be in the same units as each other.

Example

package main

import (
	"fmt"

	"github.com/mooncaker816/learnmeeus/v3/moonillum"
	"github.com/soniakeys/unit"
)

func main() {
	i := moonillum.PhaseAngleEq(
		unit.RAFromDeg(134.6885),
		unit.AngleFromDeg(13.7684),
		368410,
		unit.RAFromDeg(20.6579),
		unit.AngleFromDeg(8.6964),
		149971520)
	fmt.Printf("i = %.4f\n", i.Deg())
}

Output:

i = 69.0756

func PhaseAngleEq2

func PhaseAngleEq2(α unit.RA, δ unit.Angle, α0 unit.RA, δ0 unit.Angle) unit.Angle

PhaseAngleEQ2 computes the phase angle of the Moon given equatorial coordinates.

Less accurate than PhaseAngleEq.

Arguments α, δ are geocentric right ascension and declination of the Moon; α0, δ0 are coordinates of the Sun.

Example

package main

import (
	"fmt"

	"github.com/mooncaker816/learnmeeus/v3/base"
	"github.com/mooncaker816/learnmeeus/v3/moonillum"
	"github.com/soniakeys/unit"
)

func main() {
	i := moonillum.PhaseAngleEq2(
		unit.RAFromDeg(134.6885),
		unit.AngleFromDeg(13.7684),
		unit.RAFromDeg(20.6579),
		unit.AngleFromDeg(8.6964))
	k := base.Illuminated(i)
	fmt.Printf("k = %.4f\n", k)
}

Output:

k = 0.6775