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:

``js
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":

`js
import { Moon } from "lunarphase-js";

const phase = Moon.lunarPhase();
`

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

`js
import { Moon } from "lunarphase-js";

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




$3

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

`js
const phase = Moon.lunarPhase();
`




$3

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

`js
const phaseEmoji = Moon.lunarPhaseEmoji();
`

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

`js
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:

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

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

Optionally pass a Hemisphere to the function:

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

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

`




$3

Whether the moon is waxing (ex: false)

`js
const waxing = Moon.isWaxing();
`




$3

Whether the moon is waning (ex: true)

`js
const waning = Moon.isWaning();
`




$3

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)

`js
const age = Moon.lunarAge();
`




$3

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

`js
const agePercent = Moon.lunarAgePercent();
`




$3

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

`js
const lunationNumber = Moon.lunationNumber();
`




$3

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

`js
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:

`js
import { Julian } from "lunarphase-js";

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

To convert a Julian day to a date:

`js
import { Julian } from "lunarphase-js";

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