Calculate sunrise, sunset, and twilight times for a given location and date.

Goals

1. Given a location and a date provide:
   • Sunrise date and time for that location
   • Sunset date and time for that location
   • Solar Noon date and time (when the sun is overhead)
   • Dawn and Dusk (twilight) dates and times for that location:
     • Civil
     • Nautical
     • Astronomical
2. Allow the user to disable some calculations (e.g., only calculate Official) when run.

API

There is only one class: FESSolarCalculator

• pass in date and time to get back new object with -initWithDate:location:
• limit what calculations are done with -initWithDate:location:mask:
  • see the FESSolarCalculationType enum for the types of calculations
• property readonly: NSDate startDate
• property readonly: CLLocation location
• property readonly: NSDate sunrise (Official)
• property readonly: NSDate sunset (Official)
• property readonly: NSDate solarNoon
• property readonly: NSDate civilDawn
• property readonly: NSDate civilDusk
• property readonly: NSDate nauticalDawn
• property readonly: NSDate nauticalDusk
• property readonly: NSDate astronomicalDawn
• property readonly: NSDate astronomicalDusk

Note: Properties will be nil if the calculations have not been run or if they were outside the calculation mask.

In addition there are two class methods that are provided as a utility:

• +julianDayNumberFromDate:
• +dateFromJulianDayNumber:

These are provided to convert to and from Julian Day Numbers. Normally one would just use the 'g' format option to NSDateFormatter, however in developing this a bug was discovered that converts to and from the wrong hour on a given day. See http://openradar.appspot.com/11023565 for details. These will be revisited or removed when or if that bug is resolved.

Usage

See the examples in the source. It is recommended that your start date is at noon, but it can be any time on a given day.

Issues

There one known issue:

• Need to handle the sun never rising or setting for a given location

Check the issues page for the project for the latest status.

Precision

The precision is likely around three minutes, mostly due to approximation. Also, this calculation does not take into account the effect of air temperature, altitude, etc. Together, these may affect the time by 5 minutes or more. This is likely not what you need if you are in need of a very precise solar calculation.

Note that dates prior to 01 January 2000 GMT are not guarenteed to return correct results at this time (if ever).

Automatic Reference Counting (ARC)

The source code in this repository uses Automatic Reference Counting. No plans exist to support non-ARC code. If your project requires non-ARC code compile these files with -fobjc-arc. See the clang docs for more details.

License

This code is licensed under the MIT license. The license is reproduced below. If a non-attribution license is required contact Daniel Weeks for details:

Copyright © 2012 Daniel Weeks.

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the “Software”), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.