Sun is a simple javascript utility class to integrate into a website for sunrise/sunset and twilights times calculations. Later on, this should also include calculation of the current year's equinoxes.
This code is based on the work of Dr Louis Strous at http://www.astro.uu.nl/~strous/AA/en/index.html Specifically, these calculations implement his equations and use his constant values found at http://www.astro.uu.nl/~strous/AA/en/reken/zonpositie.html Twilight angles estimations are taken from: Van Flandern, T.; K. Pulkkinen (1980). "Low precision formulae for planetary positions". Astrophysical Journal, Supplement Series 31 (3). http://adsabs.harvard.edu/abs/1979ApJS...41..391V
Simply include the file in your HTML <head> tag as follows:
<script type="text/javascript" src="js/Sun.js"></script>
On your page, or in a separate script, simply create a new instance of Sun, passing the desired date, latitude and longitude you want to calculate the sunrise and sunset for: Latitudes and longitudes must be expressed as decimal numbers, positive latitudes being North, and positive longitudes being West.
// decimal below correspond to: 51°30′26″N 0°7′39″W
var latitude = 51.507222,
longitude = 0.1275,
theSun = new Sun(new Date(), latitude, longitude);
The sunrise, solar transit, and sunset, times are available on the instance. They will be returned in an array containing the following: [day, month, year, hours, minutes, seconds]
var solarTransitTime = theSun.daySolarTransit,
sunRiseTime = theSun.sunRiseDateParts,
sunsetTime = theSun.sunSetDateParts;
Likewise, astronomical, nautical and twilight times for the given day are accessible through:
var sunRiseAstronomicalTwilightTime = theSun.sunRiseAstronomicalTwilightDateParts,
sunRiseNauticalTwilightTime = theSun.sunRiseNauticalTwilightDateParts,
sunRiseCivilTwilightTime = theSun.sunRiseCivilTwilightDateParts,
sunSetCivilTwilightTime = theSun.sunSetCivilTwilightDateParts,
sunSetNauticalTwilightTime = theSun.sunSetNauticalTwilightDateParts,
sunSetAstronomicalTwilightTime = theSun.sunSetAstronomicalTwilightDateParts;
I'll try to add calculation of the chosen year's equinoxes later on!
Mathieu Davy - Ekynoxe, 2011