SunCalc is a tiny, dependency-free JavaScript library for calculating sun position, sunlight phases (sunrise, sunset, dusk, etc.), moon position, moonrise and moonset times, and lunar phase for any location and time.

It matches the accuracy and conventions of timeanddate.com and the U.S. Naval Observatory. Calculations are based on the formulas from Jean Meeus' Astronomical Algorithms. You can read about different twilight phases calculated by SunCalc in the Twilight article on Wikipedia.

Example

import * as SunCalc from 'suncalc';

const times = SunCalc.getTimes(new Date(), 51.5, -0.1); // get today's sunlight times for London
console.log(`Sunrise time: ${times.sunrise.toLocaleString()}`);

const sunrisePos = SunCalc.getPosition(times.sunrise, 51.5, -0.1); // get Sun position at today's sunrise
console.log(`Sunrise direction: ${sunrisePos.azimuth} degrees`);

Install

Install with npm: npm install suncalc, then import it as a module:

import * as SunCalc from 'suncalc';

Or use it directly in the browser via jsDelivr:

<script type="module">
    import * as SunCalc from 'https://cdn.jsdelivr.net/npm/suncalc/+esm';
</script>

Alternatively, there's a browser bundle that exposes a SunCalc global variable:

<script src="https://cdn.jsdelivr.net/npm/suncalc"></script>

Reference

Sun position

SunCalc.getPosition(date, lat, lng)

Returns an object with the following properties:

• altitude: apparent (refraction-corrected) sun altitude above the horizon in degrees, e.g. 0 at the horizon and 90 at the zenith (straight overhead)
• azimuth: sun azimuth in degrees, clockwise from north (0 = N, 90 = E, 180 = S, 270 = W)

Sunlight times

SunCalc.getTimes(date, lat, lng, height = 0)

Returns sunlight times for the solar day containing date, at the given latitude, longitude and (optional) observer height above the horizon in meters.

The result is an object whose properties are Date objects (or null when the event doesn't occur that day). Listed in the order they occur over the solar day, with example times for Kyiv (50.45°N, 30.52°E) on 24 August 2026, shown in local time (EEST, UTC+3):

solarNoon and nadir are always present. At high latitudes, when the sun stays above or below the rise/set altitude for the whole day, the rise/set-related times are null and one of these flags is set:

• alwaysUp: true when the sun never sets that day (polar day)
• alwaysDown: true when the sun never rises that day (polar night)

The returned Dates are absolute UTC instants with no time zone of their own (as everywhere in SunCalc). To show one in a specific zone, format it with an explicit timeZone — daylight saving time is then applied for you:

times.sunset.toLocaleString('en-GB', {timeZone: 'Europe/Kyiv'}); // → "24/08/2026, 19:59:00"

With no timeZone, toLocaleString uses the machine's local zone, so the same code prints different clock times on different machines.

SunCalc.addTime(angleInDegrees, morningName, eveningName)

Adds a custom time when the sun reaches the given altitude angle (in degrees) to the results returned by SunCalc.getTimes. The morningName is used for the ascending (morning) crossing and eveningName for the descending (evening) one.

SunCalc.times contains all currently defined times as [angleInDegrees, morningName, eveningName] rows.

For example, to add the blue hour (roughly −4° to −8°) with your own preferred angles:

SunCalc.addTime(-4, 'morningBlueHourEnd', 'blueHour');
SunCalc.addTime(-8, 'morningBlueHour', 'blueHourEnd');

Moon position

SunCalc.getMoonPosition(date, lat, lng)

Returns an object with the following properties:

• altitude: apparent moon altitude above the horizon in degrees
• azimuth: moon azimuth in degrees, clockwise from north
• distance: distance to the moon in kilometers
• parallacticAngle: parallactic angle of the moon in degrees

Moon illumination

SunCalc.getMoonIllumination(date)

Returns an object with the following properties:

• fraction: illuminated fraction of the moon; varies from 0.0 (new moon) to 1.0 (full moon). It reaches the exact extremes only at perfect syzygy (eclipses), so a "full" moon typically peaks a hair under 1.0
• phase: moon phase; varies from 0.0 to 1.0, described below
• angle: position angle of the bright limb in degrees, reckoned eastward from the north point of the disk
• waxing: true while the moon is waxing (new → full), false while waning (full → new)

The phase value maps to the named phases like this:

The four named values (0, 0.25, 0.5, 0.75) are exact instants; any other value falls in one of the crescent/gibbous ranges between them. So phase: 0.4945… is not "Full Moon" — it's late Waxing Gibbous, just shy of full. To map a value to one of the eight names, snap it to the nearest one-eighth:

const names = ['New Moon', 'Waxing Crescent', 'First Quarter', 'Waxing Gibbous',
               'Full Moon', 'Waning Gibbous', 'Last Quarter', 'Waning Crescent'];
const {phase} = SunCalc.getMoonIllumination(new Date());
const name = names[Math.round(phase * 8) % 8];

Use phase for the name and fraction for how lit the disk is — and since fraction only reaches an exact 0 or 1 at an eclipse, don't test it for equality with those.

By subtracting getMoonPosition().parallacticAngle from angle (both in degrees) you get the zenith angle of the moon's bright limb (anticlockwise). The zenith angle can be used to draw the moon's shape from the observer's perspective (e.g. moon lying on its back).

Moon rise and set times

SunCalc.getMoonTimes(date, lat, lng)

Returns an object with the following properties:

• rise: moonrise time as a Date
• set: moonset time as a Date
• alwaysUp: true if the moon is always above the horizon during the day
• alwaysDown: true if the moon is always below the horizon

Unlike the sun, the moon can rise and set zero, one, or two times within a single day, so this function scans a fixed 24-hour window: the UTC calendar day of the given date (consistent with the rest of the API, which treats dates as UTC instants). If you want the window to follow an observer's local civil day, pass a date set to their local midnight.

Accuracy

Every function is built on higher-order astronomical models from Jean Meeus' Astronomical Algorithms and validated against JPL Horizons and the U.S. Naval Observatory. Typical errors:

Rise and set times are accurate to ~15 seconds — at the floor of what the USNO's whole-minute reference data can even measure.

Changelog

See the Releases page for the full changelog. Note that v2.0 is a precision-focused rewrite with breaking changes to units and conventions — see its release notes before upgrading.