Sidereal

Sidereal is a JavaScript library designed for astronomical calculations.

It provides a set of APIs for determining the positions of celestial bodies, their celestial observables and performing orbital transfers and other related calculations.

Features

• Celestial Body Positions: Calculate the positions of planets, stars, and other celestial objects.
• Celestial Observables: Retrieve various observable attributes of celestial bodies, including apparent magnitudes, rise and set times, and current constellation information.
• Orbital Transfers: Perform calculations for orbital transfers and related computations.

Installation

To install Sidereal, use npm:

npm install sidereal

Documentation

Comprehensive documentation and API details will be available on the official website in the near future. Stay tuned for updates!

Accuracy

Sidereal provides accurate astronomical calculations using built-in algorithms, but to keep the bundle size small, it does not include precomputed ephemerides. As a result, there may be a modest margin of error in the calculations. See the Basic usage section below to understand the scale of this error.

For higher precision, you can use Sidereal with Sidereal-Ephemeris, which incorporates JPL ephemerides. Together, they can achieve errors as small as 0.0832° as shown in this example.

For more on Sidereal-Ephemeris, visit the GitHub repository.

Basic usage

Here is a basic example of how to use Sidereal to get the position of a celestial body:

import Sidereal from "sidereal";

const sidereal = new Sidereal();

const mars = sidereal.planet('mars');

const date = new sidereal.AstroDate(2024, 6, 22, 0, 0)
const coordinatesCenter = "earth";

const marsPosition = mars.getPositionAtDate(date, coordinatesCenter);

const { spherical, cartesian } = marsPosition.getEquatorialCoords();

console.log('Geocentric equatorial coordinates of Mars on 22th June 2024 at 00:00 UTC');
console.log('Cartesian: (', cartesian.x, ',', cartesian.y, ',', cartesian.z, ')' )
console.log('Spherical: (', spherical.RA.HMS(), ',', spherical.DEC.DMS(), ')' )

Result:

Geocentric equatorial coordinates of Mars on 22th June 2024 at 00:00 UTC
Cartesian: ( 1.3514278051653246 , 1.0349003612244017 , 0.47248222985938937 )
Spherical: ( 02h 29m 47s , +15° 30' 48" )

Expected result [J2000]

RA 02h 28m 04s  Dec  +13° 32' 18"

RA error = 0.5417°
Dec error = 1.975°
Total Angular error: 2.043°

Usage with sidereal-ephemeris

import Sidereal from "sidereal";
import { loadEphemeris } from "sidereal-ephemeris";


const sidereal = new Sidereal();

const venusEphemeris = loadEphemeris('venus');
const earthEphemeris = loadEphemeris("earth");

sidereal.useEphemeris([venusEphemeris, earthEphemeris])

const venus = sidereal.planet('venus');

const date = new sidereal.AstroDate(2020, 6, 22, 0, 0)
const coordinatesCenter = "earth";

const marsPosition = venus.getPositionAtDate(date, coordinatesCenter);

const { spherical } = marsPosition.getEquatorialCoords();


console.log('RA', spherical.RA.HMS(), ', Dec', spherical.DEC.DMS(), ')' )

Result

RA 04h 15m 44s Dec +18° 02' 45" 

Expected result (J2000)

RA 04h 15m 46s  Dec  +18° 02' 46"
RA error: 0.0833°
Dec error: 0.0042°
Total angular error: 0.0832°

License

Sidereal is licensed under the MIT License.