parallactic

Documentation

Overview

Parallactic: Chapter 14, The Parallactic Angle, and three other Topics.

Index

• func DiurnalPathAtHorizon(δ, φ unit.Angle) (J unit.Angle)
• func EclipticAtEquator(λ, ε unit.Angle) unit.Angle
• func EclipticAtHorizon(ε, φ unit.Angle, θ unit.Time) (λ1, λ2, I unit.Angle)
• func ParallacticAngle(φ, δ unit.Angle, H unit.HourAngle) unit.Angle
• func ParallacticAngleOnHorizon(φ, δ unit.Angle) unit.Angle

Examples

• EclipticAtHorizon

Functions

func DiurnalPathAtHorizon

func DiurnalPathAtHorizon(δ, φ unit.Angle) (J unit.Angle)

DiurnalPathAtHorizon computes the angle of the path a celestial object relative to the horizon at the time of its rising or setting.

δ is declination of the object.
φ is geographic latitude of observer.

func EclipticAtEquator

func EclipticAtEquator(λ, ε unit.Angle) unit.Angle

EclipticAtEquator computes the angle between the ecliptic and the parallels of ecliptic latitude at a given ecliptic longitude.

(The function name EclipticAtEquator is for consistency with the Meeus text, and works if you consider the equator a nominal parallel of latitude.)

λ is ecliptic longitude.
ε is obliquity of the ecliptic.

func EclipticAtHorizon

func EclipticAtHorizon(ε, φ unit.Angle, θ unit.Time) (λ1, λ2, I unit.Angle)

EclipticAtHorizon computes how the plane of the ecliptic intersects the horizon at a given local sidereal time as observed from a given geographic latitude.

ε is obliquity of the ecliptic.
φ is geographic latitude of observer.
θ is local sidereal time.

λ1 and λ2 are ecliptic longitudes where the ecliptic intersects the horizon.
I is the angle at which the ecliptic intersects the horizon.

Example

ε := unit.AngleFromDeg(23.44)
φ := unit.AngleFromDeg(51)
θ := unit.TimeFromHour(5)
λ1, λ2, I := parallactic.EclipticAtHorizon(ε, φ, θ)
fmt.Println(sexa.FmtAngle(λ1))
fmt.Println(sexa.FmtAngle(λ2))
fmt.Println(sexa.FmtAngle(I))

Output:

169°21′30″
349°21′30″
61°53′14″

func ParallacticAngle

func ParallacticAngle(φ, δ unit.Angle, H unit.HourAngle) unit.Angle

ParallacticAngle returns parallactic angle of a celestial object.

φ is geographic latitude of observer.
δ is declination of observed object.
H is hour angle of observed object.

func ParallacticAngleOnHorizon

func ParallacticAngleOnHorizon(φ, δ unit.Angle) unit.Angle

ParallacticAngleOnHorizon is a special case of ParallacticAngle.

The hour angle is not needed as an input and the math inside simplifies.