(JavaScript) https://github.com/mourner/suncalc/blob/master/suncalc.js
(IDL) http://idlastro.gsfc.nasa.gov/ftp/pro/astro/mphase.pro
(Math) http://aa.quae.nl/en/index.html
NASA: http://www.nasa.gov/connect/artspace/participate/royalty_free_resources.html
BDAstroCalc is (currently) a simple struct, written in Swift, for low-precision calculations of commonly needed properties of Earth's sun and moon, such as rise/set times, altitude/azimuth, declination/right-ascension, etc.. It was created because while there are such things in other languages, I couldn't find one written in Swift. The project for which I wrote it didn't require any precision so this was sufficient; if there's any demand then I'll be happy to update BDAstroCalc to be more sophisticated.
The iOS project/demo is not meant to be a polished app. It is simply to demonstrate the results and to provide an example of use.
I have tried to provide fairly thorough commenting throughout the file. Do pay attention to the notes below; the work on which this was based sometimes does not abide by standards, so a couple of conversions need to be done if you're presenting the results. (The Demo UILabels reflect this.) I will update the methods to follow standards if there are any requests for it.
The SunCalc code, which served as the basis for BDAstroCalc, was JavaScript; its reference code (when you dig back) was largely in IDL written for the USNO and NASA. The USNO/NASA commenting was fairly thorough, but over the translations the commenting has gotten more and more sparse. I've tried to decipher what's what, but I may have guessed wrong here or there--I'll happily update anything you notice that needs updating. As with any astronomical calculations there are a LOT of magic numbers; I've tried to include references to explanations where I've found them (though this process will be ongoing).
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Pay close attention to your timezone after retrieving results. If you look through the SunCalc Github issues, many were just timezone-related.
a) In SunCalc everything returns in radians EXCEPT the longitude and latitude of moonPositon, moonRiseAndSet, sunPosition, and sunRiseAndSet. To reduce confusion I've made those that take degrees require CLLocationCoordinate2D; 'longitude' and 'latitude' parameters are always in radians. All returns are in radians.
b) A further complication: it seems that for convenience reasons longitude was made to be the "longitude west of the prime meridian" and latitude the "latitude north of the equator". The latter is normal, of course, but the former is negating the norm. This applies only to non-CLLocationCoordinate2D longitude. This won't matter if you're only using moonPositon, moonRiseAndSet, sunPosition, and sunRiseAndSet.
c) If for some reason you don't want to import CoreLocation you can simply change the relevant function definitions to use longitude/latitude (in degrees).
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Azimuth here is measured from South to West; the norm is from North to East. Just add/subtract Pi to the result to match with results elsewhere.
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The moon rise and set vary a lot over time so that sometimes the rise is on the day before the set, sometimes the rise is on the day after the set, sometimes there is a set and no rise, sometimes a rise and no set. The returned results will reflect that: the day of the rise and set might be different.
Simply copy the BDAstroCalcDemo\BDAstroCalc.swift file into your project. Note: v1.0.1 requires Xcode 6.3 and Swift 1.2.
Everything is static so that you don't need to instantiate--just call the methods on the struct itself.
The demo app code will serve as the most useful example. To use BDAstroCalc simply send the messages to the struct itself:
let myDate = NSDate()
let myLocationCoordinates = CLLocationCoordinates2D(latitude: myLatitude, longitude: myLongitude)
let moonRiseAndSetTimes = BDAstroCalc.moonRiseAndSet(date: myDate, location: myLocation)
println(moonRiseAndSetTimes.rise) // Prints the NSDate of the moon rise The BDAstroCalcDemo project exists to demonstrate the results of BDAstroCalc.
Note: the iOS Simulator for Xcode uses your computer's time zone when NSTimeZone.systemTimeZone is called; changing your location in the Simulator's Scheme has no effect. If you want to check results for different locations you'll need to change both the Scheme location and your system time zone. Let's hope Apple fixes this soon! On real hardware this isn't a problem.
Note on the Note: this doesn't affect BDAstroCalc computations. This is only a possible issue when you're presenting results, as time zone offsets become apparent.
We would really appreciate you letting us know if you make use of BDAstroCalc or any of our other open source!
Please feel free to report issues, or offer suggestions, here on GitHub.
Alternatively, email support@braindrizzlestudio.com
or visit us at http://www.braindrizzlestudio.com
####1.0.2
- Updated syntax for iOS 9
####1.0.1
- Updated Demo/BDAstroCalc for Xcode 6.3 and Swift 1.2