Galactic

Celestial coordinate conversions and utilities

Usage

The following examples use some basic transforms:

var rad = function(deg) { return deg/180 * Math.PI; };
var deg = function(rad) { return rad*180 / Math.PI; };

Where is alpha centauri in the sky above Toronto right now?

// Create coordinate in equatorial coordinate system
var centauri = galactic({latitude: rad(-42.587), longitude: rad(239.488)});

// Observer (Toronto, now)
var observer = {latitude: rad(43.7001100), longitude: rad(-79.4163000), utc: Date.now()};

// Convert to horizontal given observer place/time
var horizontal = centauri.horizontal( observer );

// Where is it?
console.log('Altitude: ' + deg(horizontal.altitude()) + ', Azimuth: ' + deg(horizontal.azimuth()));

Where is the sun in the skies of Toronto?

// Create coordinate in equatorial coordinate system
// Calculate sun's mean longitude (approx)
var n = galactic.dates.unixDateToJulian(Date.now()) - galactic.dates.J2000
var meanLongitude = 280.46 + 0.9856474*n
var sun = galactic({longitude: rad(meanLongitude), latitude: 0});

// Observer (Toronto, now)
var observer = {latitude: rad(43.7001100), longitude: rad(-79.4163000), utc: Date.now()};

// Convert to horizontal given observer place/time
var horizontal = sun.horizontal( observer );

// Where is it?
console.log('Sun - Altitude: ' + deg(horizontal.altitude()) + ', Azimuth: ' + deg(horizontal.azimuth()));

Building

npm install
grunt

AMD and CJS compatible formats will be created in dist/

To Do

• Document API
• Example usage
• Clean up coordinate transforms API supporting multiple coord formats
• Extract celestial body definitions to generalize
• Add handy additional functions, e.g. sun and moon positions given date
• NPM prepublish compile step