suncalc

A tiny JavaScript library for calculating sun/moon positions and phases.

SunCalc

SunCalc is a tiny BSD-licensed JavaScript library for calculating sun position, sunlight phases (times for sunrise, sunset, dusk, etc.), moon position and lunar phase for the given location and time, created by Vladimir Agafonkin (@mourner) as a part of the SunCalc.net project.

Most calculations are based on the formulas given in the excellent Astronomy Answers articles about position of the sun and the planets. You can read about different twilight phases calculated by SunCalc in the Twilight article on Wikipedia.

// get today's sunlight times for London 
var times = SunCalc.getTimes(new Date(), 51.5, -0.1);
 
// format sunrise time from the Date object 
var sunriseStr = times.sunrise.getHours() + ':' + times.sunrise.getMinutes();
 
// get position of the sun (azimuth and altitude) at today's sunrise 
var sunrisePos = SunCalc.getPosition(times.sunrise, 51.5, -0.1);
 
// get sunrise azimuth in degrees 
var sunriseAzimuth = sunrisePos.azimuth * 180 / Math.PI;

SunCalc is also available as an NPM package:

$ npm install suncalc
var SunCalc = require('suncalc');
SunCalc.getTimes(/*Date*/ date, /*Number*/ latitude, /*Number*/ longitude)

Returns an object with the following properties (each is a Date object):

Property Description
sunrise sunrise (top edge of the sun appears on the horizon)
sunriseEnd sunrise ends (bottom edge of the sun touches the horizon)
goldenHourEnd morning golden hour (soft light, best time for photography) ends
solarNoon solar noon (sun is in the highest position)
goldenHour evening golden hour starts
sunsetStart sunset starts (bottom edge of the sun touches the horizon)
sunset sunset (sun disappears below the horizon, evening civil twilight starts)
dusk dusk (evening nautical twilight starts)
nauticalDusk nautical dusk (evening astronomical twilight starts)
night night starts (dark enough for astronomical observations)
nadir nadir (darkest moment of the night, sun is in the lowest position)
nightEnd night ends (morning astronomical twilight starts)
nauticalDawn nautical dawn (morning nautical twilight starts)
dawn dawn (morning nautical twilight ends, morning civil twilight starts)
SunCalc.addTime(/*Number*/ angleInDegrees, /*String*/ morningName, /*String*/ eveningName)

Adds a custom time when the sun reaches the given angle to results returned by SunCalc.getTimes.

SunCalc.times property contains all currently defined times.

SunCalc.getPosition(/*Date*/ timeAndDate, /*Number*/ latitude, /*Number*/ longitude)

Returns an object with the following properties:

  • altitude: sun altitude above the horizon in radians, e.g. 0 at the horizon and PI/2 at the zenith (straight over your head)
  • azimuth: sun azimuth in radians (direction along the horizon, measured from south to west), e.g. 0 is south and Math.PI * 3/4 is northwest
SunCalc.getMoonPosition(/*Date*/ timeAndDate, /*Number*/ latitude, /*Number*/ longitude)

Returns an object with the following properties:

  • altitude: moon altitude above the horizon in radians
  • azimuth: moon azimuth in radians
  • distance: distance to moon in kilometers
SunCalc.getMoonIllumination(/*Date*/ timeAndDate)

Returns an object with the following properties:

  • fraction: illuminated fraction of the moon; varies from 0.0 (new moon) to 1.0 (full moon)
  • phase: moon phase; varies from 0.0 to 1.0, described below
  • angle: midpoint angle in radians of the illuminated limb of the moon reckoned eastward from the north point of the disk; the moon is waxing if the angle is negative, and waning if positive

Moon phase value should be interpreted like this:

Phase Name
0 New Moon
Waxing Crescent
0.25 First Quarter
Waxing Gibbous
0.5 Full Moon
Waning Gibbous
0.75 Last Quarter
Waning Crescent
SunCalc.getMoonTimes(/*Date*/ date, /*Number*/ latitude, /*Number*/ longitude[, inUTC])

Returns an object with the following properties:

  • rise: moonrise time as Date
  • set: moonset time as Date
  • alwaysUp: true if the moon never rises/sets and is always above the horizon during the day
  • alwaysDown: true if the moon is always below the horizon

By default, it will search for moon rise and set during local user's day (frou 0 to 24 hours). If inUTC is set to true, it will instead search the specified date from 0 to 24 UTC hours.

  • Added inUTC argument to getMoonTimes.
  • Added SunCalc.getMoonTimes for calculating moon rise and set times.
  • Exposed SunCalc.times property with defined daylight times.
  • Slightly improved SunCalc.getTimes performance.
  • Added phase to SunCalc.getMoonIllumination results (moon phase).
  • Switched from mocha to tape for tests.
  • Added SunCalc.getMoonIllumination (in place of getMoonFraction) that returns an object with fraction and angle (angle of illuminated limb of the moon).
  • Added SunCalc.getMoonFraction function that returns illuminated fraction of the moon.
  • Added SunCalc.getMoonPosition function.
  • Added nadir (darkest time of the day, middle of the night).
  • Added tests.
  • Published to NPM.
  • Added SunCalc.addTime function.
  • First commit.