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Civil Twilight Calculator by Aviametrix, LLC
Skyclock Latest Version v1.5-4-gbbc2b37 for Android
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Civil Twilight Calculator on the App Store
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Sun/Moon Calculator Reference
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Civil Twilight Calculator by Aviametrix, LLC
Sunrise, Sunset, and Twilight - Science Pickle
Sun rise, set and twilight times calculated using a simple iterative scheme and implemented as a QBASIC program, an Excel spreadsheet using VBA and as a plain spreadsheet.