This console application has a Moon static class that allows users to calculate the current phase of the moon.

We use the last known New Moon to calculate the next full moon. The moon phases in a cycle of 29.53 days and there are milestones along the way.

public const string NewMoon = "New Moon";
public const string WaxingCrescent = "Waxing Crescent";
public const string FirstQuarter = "First Quarter";
public const string WaxingGibbous = "Waxing Gibbous";
public const string FullMoon = "Full Moon";
public const string WaningGibbous = "Waning Gibbous";
public const string ThirdQuarter = "Third Quarter";
public const string WaningCrescent = "Waning Crescent";

Calculations are based off of this pdf found on the internet.

This library also outputs the emoji for the moon in its current phase. We can also account for the look of the moon based on which hemisphere the onlooker is viewing from.

🌗 First Quarter (6.98 days)
🌖 Waxing Gibbous (7.98 days)
🌕 Full Moon (13.98 days)
🌓 Third Quarter (21.98 days)
🌑 New Moon (0.45 days)

Using the the Moon class is straighforward.

Now uses DateTime.Now which is converted to UTC. Given the date and time, we can calculate the phase of the moon.

var result = Moon.Now(/* optional hemisphere */);
Console.WriteLine(result);

UtcNow is similar to Now but uses DateTime.UtcNow.

var result = Moon.UtcNow(/* optional hemisphere */);
Console.WriteLine(result);

Calculate allows users to calculate the phase of the moon.

var dates = new[] {
    new DateTime(2020, 7, 27), new DateTime(2020, 7, 28),
    new DateTime(2020, 8, 3), new DateTime(2020, 8, 11),
    new DateTime(2020, 8, 19),
};

var results =
    dates
        .Select(x => Moon.Calculate(x))
        .Select((r, i) => $"{r.Emoji} {r.Name} ({r.DaysIntoCycle} days)\n")
        .Aggregate((a, v) => a + v);

With an output of:

🌗 First Quarter (6.98 days, Visibility 47.27%)
🌖 Waxing Gibbous (7.98 days, Visibility 54.05%)
🌕 Full Moon (13.98 days, Visibility 94.68%)
🌓 Third Quarter (21.98 days, Visibility 51.13%)
🌑 New Moon (0.45 days, Visibility 3.05%)

• Moon : The Earth's Moon with methods like Now, UtcNow, and Calculate.
• Earth.Hemispheres : an enum with values of Northern and Southern, used to determine the look of the moon.
• PhaseResult: includes properties like Name, Emoji, DaysIntoCycle, Hemisphere, and Moment.

The calculation is not that exact because it also depends on your location on Earth. The phase of the moon could look slightly different for someone living in Los Angeles, California compared to someone living in Helsinki, Finland.

The library uses UTC as a median point to determine what the moon will look like at UTC, both in time and location.

If you need more exact moon phases, you'll need to use a web service and make HTTP calls.

This library uses the last known new moon I could find on record, which is January 21st, 1920 at 5:25 AM over London, England.

// London New Moon (1920)
// https://www.timeanddate.com/moon/phases/uk/london?year=1920
var daysSinceLastNewMoon =
    new DateTime(1920, 1, 21, 5, 25, 00, DateTimeKind.Utc).ToOADate() + julianConstant;

Copyright 2020 Khalid Abuhakmeh

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