[WatchFace] Black Pearl - Yemaya - ver.2

Version 2 published today ( 10th March )

Apart from a minor fix to the rotation of the bracket that holds the “moon-let” as moves around its track, the main change is the inclusion of the battery meter.

And, of course, the second hand and mermaid are now clothed in sky blue.

Updated ( again ) today ( 6 March 2019 )

  • replaced moon images with new ones - dark part of moon is brighter
  • aligned the timing of the images to the actual moon phase and the indicator ( I noticed that the timing of the original images was significantly off )

And a second version, with a simple second hand, for those who don’t like mermaids :slight_smile:

Updated today ( 2 March 2019 ):

  • more accurate moon phase formula greatly improves accuracy of moon phase prediction
  • simple formula, with max error of +/- 19 hours, replaced with more complex expression reducing the maximum error down to 1 hour and median down to 19 minutes.

Old thread continues below …

Yemaya, goddess of the ocean and the moon, sometimes appears as beautiful woman or mermaid watching over those who venture into the sea.

This “Yemaya” model of my Black Pearl watch face features:

  • Large and bright numbers and hands making it easy to tell the time at glance, even in the “dark ocean”;

  • A window into the sky shows the moon as it changes during the month and a small silver moon-let rotates in its track around the outside of the window to indicate the age of the moon in days;

  • Sunrise and Sunset markers, yellow for sunrise and red for sunset, rotate near the outside of the face to show the times; and, of course

  • your very own mermaid watches over you as explore the depths …


I think I am almost ready to publish, before I do so, I would love to know what you think.



Oh, and for those interested in such things, the formula I used for the moon phase was


This gives the age of the moon in days ( assuming a fixed lunar synodic period ).

The number 585122000 is the time in milliseconds between the 1 Jan 1970 ( the start date for the #DNOW# tag ) and what would have been the approximate date/time for the first new moon after that date if the synodic period was constant. This number was obtained empirically by recursively solving for the “new moon date/time” in order to minimise the RMS value of the difference between the full moon dates/times predicted by the above formula and the dates/times for the full moon over the next 10 years from published tables.

This formula results in the following variation between predicted and actual date/time of the full moon ( in days ):

with an RMS value of about 0.3 days.

Choosing an actual historic new moon date as the offset in the equation, instead of a calculated value, will, in general, produce a significant offset to the above curve, and thus exacerbating the already quite large “error” between the average synodic period based prediction and the actual moon phase.

If you want to convert between the “Unix timestamp” ( given by #DNOW# ) and human readable date/time you can use the online tools at:

for example, 585122000 is equivalent to GMT: Wednesday, January 7, 1970 6:32:02 PM
( versus the actual new moon time of 7 Jan 8:35 pm; using this time would add an additional constant offset/error to the prediction formula of around 3hrs ).

Note that the timestamp entry in the tool is in seconds ( so, eg. 585122000 / 1000 )

Truly accurate values/predictions for the dates and times of past and future moon phases can be obtained from the US Naval Observatory - https://aa.usno.navy.mil/data/docs/MoonPhase.php

Updated …

  • Increased contrast of moon images. Added additional images and adjusted timing to better align the 1/4 and 3/4 moon images with the ‘age of moon’ scale.

  • Larger “age of moon” scale, labels and moon-let indicator to make them easier to read and also to better match the scale of the rest of the face.

  • Re-arranged model text to balance the face.

And with a set of very different hands …

I can’t decide if I like them or not. I would love to know what you think :slight_smile:

wait for it… when will it published?

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Soon… I was hoping for some feedback first. I can’t decide on the best hands…

I think I might go with these hands …

You can find the published versions at the top of the thread …

Wow! That’s some serious work on the Moon phases


Thanks! I wanted to get it as close as possible to the real values using the simple model - although, given the small size of the display on the watch, an error of +/- one day or more would probably not be that noticable :slight_smile:

Yeah! Truly one of the best moon phase animations i´ve seen yet. And i have no clue how you did it.

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Thanks, that is very kind of you.

The moon window shows a series of images ( ~48 or so from memory ) taken from a version of this gif:

The transparency of each frame is set to zero except for the part of the period that corresponds to that phase.



makes the frame showing the full moon visible between 14.49 days and 15.04 days after the approximate date of the new moon.

( Note: I can not remember the link to the actual version of the moon gif I used but you could find it by searching wikimedia. This one has the text at the top overwriting the image - the one I used did not. )

Wow. So you made 48 layers? Only for the moon phase?


What a work! compliments!

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Yes I know, a tad obsessive :slight_smile:

If I would have been happy with a smaller moon, less images and/or pushing it out to a greater radius then I could have pasted the images onto a single circular image that I rotated by increments. But, with the large window I wanted, well I went with the complicated option…

Thanks for that, much appreciated :slight_smile:

Great watchface, just downloaded and love it. Only thing missing is a battery indicator for watch. Could you add that?

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That is nice to hear, I am glad you liked it :slight_smile:

I have been updating the watch fairly frequently and I will look at adding a battery indicator the next time I I do so. Mmm, I will have to find a way to do so that is in keeping with the analog / realistic theme.

Which one did you want, the one with the Mermaid or the one without?


Minor update today to improve the accuracy of the moon phase indicator …

Replacing simple formula with a more complex version reduced maximum error down from +/-19 hours to around +/- 1 hour. Most of the time the face will now indicate the correct phase of the moon to within about 20 minutes ( only occasionally will this blow out to between 20min and 1hr ).


That is great work, shows dedication… bravo

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