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.
Usage example
// 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');
Reference
Sunlight times
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.
Sun position
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 andPI/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 andMath.PI * 3/4
is northwest
Moon position
SunCalc.getMoonPosition(/*Date*/ timeAndDate, /*Number*/ latitude, /*Number*/ longitude)
Returns an object with the following properties:
altitude
: moon altitude above the horizon in radiansazimuth
: moon azimuth in radiansdistance
: distance to moon in kilometersparallacticAngle
: parallactic angle of the moon in radians
Moon illumination
SunCalc.getMoonIllumination(/*Date*/ timeAndDate)
Returns an object with the following properties:
fraction
: illuminated fraction of the moon; varies from0.0
(new moon) to1.0
(full moon)phase
: moon phase; varies from0.0
to1.0
, described belowangle
: 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 |
By subtracting the parallacticAngle
from the angle
one can get the zenith angle of the moons bright limb (anticlockwise).
The zenith angle can be used do draw the moon shape from the observers perspective (e.g. moon lying on its back).
Moon rise and set times
SunCalc.getMoonTimes(/*Date*/ date, /*Number*/ latitude, /*Number*/ longitude[, inUTC])
Returns an object with the following properties:
rise
: moonrise time asDate
set
: moonset time asDate
alwaysUp
:true
if the moon never rises/sets and is always above the horizon during the dayalwaysDown
: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.
Changelog
1.7.0 — Nov 11, 2015
- Added
inUTC
argument togetMoonTimes
.
1.6.0 — Oct 27, 2014
- Added
SunCalc.getMoonTimes
for calculating moon rise and set times.
1.5.1 — May 16, 2014
- Exposed
SunCalc.times
property with defined daylight times. - Slightly improved
SunCalc.getTimes
performance.
1.4.0 — Apr 10, 2014
- Added
phase
toSunCalc.getMoonIllumination
results (moon phase). - Switched from mocha to tape for tests.
1.3.0 — Feb 21, 2014
- Added
SunCalc.getMoonIllumination
(in place ofgetMoonFraction
) that returns an object withfraction
andangle
(angle of illuminated limb of the moon).
1.2.0 — Mar 07, 2013
- Added
SunCalc.getMoonFraction
function that returns illuminated fraction of the moon.
1.1.0 — Mar 06, 2013
- Added
SunCalc.getMoonPosition
function. - Added nadir (darkest time of the day, middle of the night).
- Added tests.
1.0.0 — Dec 07, 2011
- Published to NPM.
- Added
SunCalc.addTime
function.
0.0.0 — Aug 25, 2011
- First commit.