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Lunar phase

Calculate phase of the moon using Julian date.

Getting Started

To install, execute:

npm i lunarphase-js

Then, import into a project and use as:

import { Moon } from "lunarphase-js";

const phase = Moon.lunarPhase();

This package provides for following distributables:

  • CJS: CommonJS
  • ESM: ES Modules
  • UMD: Universal Module Definition (browser)
  • IIFE: Immediately invoked function expression
  • TypeScript declaration types

Usage

In the lunar calendar there are 8 phases each synodic month, which is the number of days to complete the cycle. This time between two identical syzygies is equivalent to 29.53059 Earth days.

Lunar phases, in order:

Phase Northern Hemisphere Southern Hemisphere
New 🌑 🌑
Waxing Crescent 🌒 🌘
First Quarter 🌓 🌗
Waxing Gibbous 🌔 🌖
Full 🌕 🌕
Waning Gibbous 🌖 🌔
Last Quarter 🌗 🌓
Waning Crescent 🌘 🌒

API Reference:

The following functions are exported from Moon:

Function Output Description
lunarPhase() Waxing Gibbous Get lunar phase for a given date
lunarPhaseEmoji() 🌖 Get emoji of lunar phase for a given date
isWaxing() true Whether the moon is waxing
isWaning() false Whether the moon is waning
lunarAge() 11.367344279004676 Earth days since the last new moon
lunarAgePercent() 0.38497186542446116 Percentage through the lunar synodic month
lunarDistance() 56.04166690080031 Distance to the moon measured in units of Earth radii
lunationNumber() 1217 Brown Lunation Number (BLN)

Visit this repository's GitHub Pages for a live example: https://jasonsturges.github.io/lunarphase-js/

All functions default to the current date, as in "now":

import { Moon } from "lunarphase-js";

const phase = Moon.lunarPhase();

Otherwise, pass a date object to each function for a specific date.

import { Moon } from "lunarphase-js";

const date = new Date();
const phase = Moon.lunarPhase(date);

Lunar Phase

To get the current lunar phase from the LunarPhase enum (ex: "FULL")

const phase = Moon.lunarPhase();

Lunar Phase Emoji

To get the current lunar phase emoji from the LunarEmoji (ex: "🌕"):

const phaseEmoji = Moon.lunarPhaseEmoji();

As phases are inverted between Northern and Southern Hemispheres, optionally pass Hemisphere options.

import { Hemisphere, Moon } from "lunarphase-js";

const date = new Date();
Moon.lunarPhaseEmoji(date, {
  hemisphere: Hemisphere.SOUTHERN,
});

To get emoji for other lunar phases, pass a LunarPhase enum:

import { LunarPhase, Moon } from "lunarphase-js";

const emoji = Moon.emojiForLunarPhase(LunarPhase.FULL);

Optionally pass a Hemisphere to the function:

import { Hemisphere, LunarPhase, Moon } from "lunarphase-js";

const emoji = Moon.emojiForLunarPhase(LunarPhase.FULL, {
  hemisphere: Hemisphere.SOUTHERN,
});

Waxing

Whether the moon is waxing (ex: false)

const waxing = Moon.isWaxing();

Waning

Whether the moon is waning (ex: true)

const waning = Moon.isWaning();

Lunar Age

Age in Earth days through the current lunar cycle, equivalent to 29.53059 Earth days, based on Mean Synodic Month, 2000 AD mean solar days.

Phase Start Event End
New 0 1.84566173161
Waxing Crescent 1.84566173161 3.69132346322 5.53698519483
First Quarter 5.53698519483 7.38264692644 9.22830865805
Waxing Gibbous 9.22830865805 11.07397038966 12.91963212127
Full 12.91963212127 14.76529385288 16.61095558449
Waning Gibbous 16.61095558449 18.4566173161 20.30227904771
Last Quarter 20.30227904771 22.14794077932 23.99360251093
Waning Crescent 23.99360251093 25.83926424254 27.68492597415
New 27.68492597415 29.53058770576

To get the lunar age (ex: 16.54412413414952)

const age = Moon.lunarAge();

Lunar Age Percent

To get the percentage through the lunar cycle (ex: 0.5602368519132597)

const agePercent = Moon.lunarAgePercent();

Lunation Number

Brown Lunation Number (BLN), per Ernest William Brown's lunar theory, defining Lunation 1 as the first new moon of 1923 at approximately 02:41 UTC, January 17, 1923

const lunationNumber = Moon.lunationNumber();

Lunar Distance

Distance to the moon measured in units of Earth radii, with perigee at 56 and apogee at 63.8.

const distance = Moon.lunarDistance();

Julian

Convert to and from Gregorian Dates to Julian Days via the Julian module.

API Reference:

Function Output Description
fromDate() 2459357.5380029744 Convert date to Julian Day
toDate() 2021-05-23T05:56:10.418Z Convert Julian Day to date

To convert a date to Julian day:

import { Julian } from "lunarphase-js";

const date = new Date();
const julian = Julian.fromDate(date);

To convert a Julian day to a date:

import { Julian } from "lunarphase-js";

const julian = 2459356.529302257;
const date = Julian.toDate(julian);