Not really, It works fine in Paris France (where I live).
… But I suppose that if it works in Paris, you could adapt it to other places by checking Moon Phases 2019 – Lunar Calendar and changing my formula accordingly.

Basically what u need to change in my formula is the “292” (2 times). Find the Day-in-year number for a new moon day.
Oh and my formula works for a moon that starts its move at 9 o’clock and ends at 3 o’clock.
Sorry explaining this in english is not that easy

I’m switching on the inspector mode if u want to check it out. Good luck though, it’s a mess.

I’ve been looking over both calculations and can’t seem to get either to give super accurate results. Some phases appear to match up with various online moon calendars. However, other dates/phases appear to be off by 1-3 days. Does anyone have some additional ideas for this?

There has got to be an API or tag that can display this as an integer or percentage.

@ eradicator09 try this tag expression :
(floor(((((floor(365.25*((#Dy#-1)+4716))+(2-floor((#Dy#-1)/100)+floor(floor((#Dy#-1)/100)/4))-1096.5+#DD#+(#DH#/24+#Dm#/1440))-2451550.1)%29.530588853)/29.530588853)*100))%

Thanks, that’s another way of looking at it. I thought I could add some accuracy to the original formula, but I discovered a small glitch. I wanted to use UTC for the current hour. Problem with UTC is there is no UTC equivalent for Dates. When I get to the mismatch between my current time zone and UTC, I’d see the moon date jump back and forth. Overall the original long version was fairly accurate.

The other primary issue is the moon orbits in an elliptic. If you’ve seen all the recent news about the Super Blue Blood Moon, then you can see that the moons phases are perfectly regular. 29.530588853 days is the mean of several hundred years of data. The actual can fluctuate from 29.18 to about 29.93 days (according to wiki). The best we can hope for is around 98-99% accuracy at any one point. Unfortunately this end up being mildly frustrating to me.

I did some additional internet searches and didn’t find any free APIs that offered any more than the 8 standard moon phases.

Anyway, here is the comparison of the 3 formulas in practice against 3/2/2018 which should be a full moon:

I am working on a face that will do the standard 8 images. Do you think it is worth evening out the full, new, 1st, and 3rd? For instance, make full 3 days long instead of just a single day.

Moon Age = (((#Dy#*12+#DM#)*30+floor(((#Dy#*12+#DM#)*7-2)/12)-floor(((#Dy#*12+#DM#)+9)/12)*2+floor(((#Dy#*12+#DM#)+45)/48)-floor(((#Dy#*12+#DM#)+1197)/1200)+floor(((#Dy#*12+#DM#)+4797)/4800)+#Dd#-730521.1)%29.5305)

and Moon Elongation ( ecliptic (celestial) longitude ) degrees
Technically, the phases New Moon, First Quarter, Full Moon, and Last Quarter are defined to occur when the excess of the apparent ecliptic (celestial) longitude of the Moon over that of the Sun is 0, 90, 180, and 270 degrees, respectively
Ref: aa.usno.navy.mil/faq/docs/moon_phases.php

synodic month = 29.53 OR 29.5305 OR 29.53058868

Moon age to degrees
360 degrees / synodic month = 12.1907857977 degrees moon age

Moon Elongation = Moon Age * 12.1907857977

Moon Elongation to Moon Illumination Percentage
0% -> 50% -> 100% -> 50% -> 0% = New Moon -> First Quarter -> Full Moon -> Last Quarter -> New Moon
floor(((1 - cos( Elongation * 0.01745)) / 2) * 100)

so Moon Illumination Percentage
± (floor(((1-cos((floor((((#Dy#*12+#DM#)*30+floor(((#Dy#*12+#DM#)*7-2)/12)-floor(((#Dy#*12+#DM#)+9)/12)*2+floor(((#Dy#*12+#DM#)+45)/48)-floor(((#Dy#*12+#DM#)+1197)/1200)+floor(((#Dy#*12+#DM#)+4797)/4800)+#Dd#-730521.1)%29.5305)*12.1907))*0.01745))/2)*100))%

( all calculations carry an accuracy of +/- ) hope this help

Thanks @Ben. The formula and example are perfect for what I need. Looks like you did what I was thinking in expanding out the ranges for the day indicators:

New:0 - 1.8
Full: 13.0 - 16.6
Last Quarter: 21.3 - 23.9
etc.