zwim / suntime

Calculates sunrise and sunset as well as different types of twilight depending on your geolocation.

Suntime

A Lua library to calculate sunrise and sunset as well as different types of twilight depending on your geolocation.

Features

The algorithm has been developed from scratch.

The implementation is very precise compared to NREL's Solar Position Algorithm (SPA) https://midcdmz.nrel.gov/spa/. Typical errors are within one minute for the next 30 years.

Some highlights:

• honor sea level,
• count in astronomical refraction (temperature dependent),
• consider relativistic aberration,
• take WGS84 geoid shape of the earth,
• include the sun and earth diameter,
• ...

Usage

See test.lua for an example.

0.) Load library:

local SunTime = require("suntime")

1.) Set your position:

SunTime:setPosition(name, latitude, longitude, timezone, height, true)

Coordinates in decimal degree: SunTime:setPosition("Innsbruck Flughafen", 47.25786, 11.35111, 1, 578, true)

or coordinates in radiant: SunTime:setPosition("Innsbruck Flughafen", 47.25786/180*math.pi, 11.35111/180*math.pi, 1, 578)

2.) Set equation of time

Default: SunTime:setAdvanced() -- advanced version valid for the next few hundred years

Optional: SunTime:setSimple() -- simple version valid for 2008-2027

3.) Set date

SunTime:setDate() -- use system settings

or

SunTime:setDate(y, m, d, dst)

SunTime:setDate(2021, 10, 30, true)

4.) Calulate times

SunTime:calculateTimes()

5.) Use the calculated times

Times are decimal hours, so 12.5 is 12:30:00. If a time does not exist the value is nil.

    self.rise
    self.set 

    self.rise_civil 
    self.set_civil 
    self.rise_nautic
    self.set_nautic 
    self.rise_astronomic 
    self.set_astronomic

    self.noon 
    self.midnight

    self.times = {}
    self.times[1]  = self.midnight and (self.midnight - 24)
    self.times[2]  = self.rise_astronomic
    self.times[3]  = self.rise_nautic
    self.times[4]  = self.rise_civil
    self.times[5]  = self.rise
    self.times[6]  = self.noon
    self.times[7]  = self.set
    self.times[8]  = self.set_civil
    self.times[9]  = self.set_nautic
    self.times[10] = self.set_astronomic
    self.times[11] = self.midnight