Practical Astronomy - JavaScript (practical-astronomy-javascript)

Algorithms from "Practical Astronomy with your Calculator or Spreadsheet" by Peter Duffett-Smith, implemented in JavaScript.

If you're interested in this topic, please buy the book! It provides far more detail and context.

Installation

npm install practical-astronomy-javascript

Usage

Example 1: Calculate date of Easter for 2024.

Create client.js:

const pa = require('practical-astronomy-javascript');

console.log(pa.paDateTime.getDateOfEaster(2024));

Run it:

node client.js

Result:

[ 3, 31, 2024 ]

Example 2: Get detailed information about the April 8 solar eclipse, for West Alexandria, Ohio

Create client.js:

const pa = require('practical-astronomy-javascript');

// Information about the observer location
var monthOfObservation = 4;
var dayOfObservation = 8;
var yearOfObservation = 2024;
var isDaylightSavings = true;
var zoneCorrectionHours = 5;
var observerLatitude = 39.74722;
var observerLongitude = -84.53639;

var [solarEclipseCertainDateDay, solarEclipseCertainDateMonth, solarEclipseCertainDateYear, utFirstContactHour, utFirstContactMinutes, utMidEclipseHour, utMidEclipseMinutes, utLastContactHour, utLastContactMinutes, eclipseMagnitude] = pa.paEclipses.solarEclipseCircumstances(dayOfObservation, monthOfObservation, yearOfObservation, isDaylightSavings, zoneCorrectionHours, observerLongitude, observerLatitude);

// Results are in universal time, so adjust them for the observer's time zone
utFirstContactHour = utFirstContactHour - ((isDaylightSavings) ? zoneCorrectionHours - 1 : zoneCorrectionHours);
utMidEclipseHour = utMidEclipseHour - ((isDaylightSavings) ? zoneCorrectionHours - 1 : zoneCorrectionHours);
utLastContactHour = utLastContactHour - ((isDaylightSavings) ? zoneCorrectionHours - 1 : zoneCorrectionHours);

console.log(`Date of eclipse:        ${solarEclipseCertainDateMonth}/${solarEclipseCertainDateDay}/${solarEclipseCertainDateYear}`);
console.log(`First contact:          ${utFirstContactHour}:${utFirstContactMinutes}`);
console.log(`Mid-eclipse (totality): ${utMidEclipseHour}:${utMidEclipseMinutes}`);
console.log(`Last contact:           ${utLastContactHour}:${utLastContactMinutes}`);
console.log(`Magnitude of eclipse:   ${eclipseMagnitude}`);

Run it:

node client.js

Result:

Date of eclipse:        4/8/2024
First contact:          13:55
Mid-eclipse (totality): 15:11
Last contact:           16:27
Magnitude of eclipse:   1.006

Links

GitHub

Documentation

NPM page

Library Functions - Status

Date/Time

• Calculate -> Date of Easter
• Convert -> Civil Date to Day Number
• Convert -> Civil Time <-> Decimal Hours
• Extract -> Hour, Minutes, and Seconds parts of Decimal Hours
• Convert -> Local Civil Time <-> Universal Time
• Convert -> Universal Time <-> Greenwich Sidereal Time
• Convert -> Greenwich Sidereal Time <-> Local Sidereal Time

Coordinates

• Convert -> Angle <-> Decimal Degrees
• Convert -> Right Ascension <-> Hour Angle
• Convert -> Equatorial Coordinates <-> Horizon Coordinates
• Calculate -> Obliquity of the Ecliptic
• Convert -> Ecliptic Coordinates <-> Equatorial Coordinates
• Convert -> Equatorial Coordinates <-> Galactic Coordinates
• Calculate -> Angle between two objects
• Calculate -> Rising and Setting times for an object
• Calculate -> Precession (corrected coordinates between two epochs)
• Calculate -> Nutation (in ecliptic longitude and obliquity) for a Greenwich date
• Calculate -> Effects of aberration for ecliptic coordinates
• Calculate -> RA and Declination values, corrected for atmospheric refraction
• Calculate -> RA and Declination values, corrected for geocentric parallax
• Calculate -> Heliographic coordinates
• Calculate -> Carrington rotation number
• Calculate -> Selenographic (lunar) coordinates (sub-Earth and sub-Solar)

The Sun

• Calculate -> Approximate and precise positions of the Sun
• Calculate -> Sun's distance and angular size
• Calculate -> Local sunrise and sunset
• Calculate -> Morning and evening twilight
• Calculate -> Equation of time
• Calculate -> Solar elongation

Planets

• Calculate -> Approximate position of planet
• Calculate -> Precise position of planet
• Calculate -> Visual aspects of planet (distance, angular diameter, phase, light time, position angle of bright limb, and apparent magnitude)

Comets

• Calculate -> Position of comet (elliptical)
• Calculate -> Position of comet (parabolic)

Binary Stars

• Calculate -> Binary star orbit data

The Moon

• Calculate -> Approximate and precise position of Moon
• Calculate -> Moon phase and position angle of bright limb
• Calculate -> Times of new Moon and full Moon
• Calculate -> Moon's distance, angular diameter, and horizontal parallax
• Calculate -> Local moonrise and moonset

Eclipses

• Calculate -> Lunar eclipse occurrence and circumstances
• Calculate -> Solar eclipse occurrence and circumstances