<p>Given the phase angle of the moon (i) on degrees (0-360), is it possible to calculate its &quot;age&quot; in days?</p>

CC BY-SA 4.0
2024-12-21T17:57:29.907Z
You could roughly approximate it by $ age=PA/360*29.5 $.  But the time taken to move a certain number of degrees isn't constant, so you need more information and a better algorithm for more accuracy.
Greg Miller
CC BY-SA 4.0
2024-12-21T18:03:51.010Z
@GregMiller I did try that however that approximation is not satisfactory. Is there another way to calculate it? My calculations are based on the book Astronomical Algorithms by Jean Meeus. I have everything calculated up to the illuminated fraction of the moon (k).
RicardoTM
CC BY-SA 4.0
2024-12-21T18:57:17.097Z
Here's a link to another approximation.  But if you can compute the phase, why not just compute the last new moon and count the days? https://www.celestialprogramming.com/snippets/moonage.html
Greg Miller
CC BY-SA 4.0
2024-12-21T21:57:06.700Z
@GregMiller: Nice snippet, but isn’t the precision a little “false advertising”? You should limit it to one or two decimals…
Pierre Paquette
CC BY-SA 4.0
2024-12-22T03:32:47.343Z
@GregMiller Because the process on the book is a little bit too much with 14 extra arguments + 25 corrections + another additional 14 corrections. Thank you, I'll try that method when I get on the PC later.
RicardoTM
CC BY-SA 4.0
2024-12-22T03:48:02.310Z
@PierrePaquette The decimals are required so the average is valid over a long range of time even though the individual predictions won't be accurate to that many decimals.
Greg Miller
CC BY-SA 4.0
2024-12-22T15:05:59.417Z
@GregMiller it works fine and way closer to the correct result. Thank you. I'd mark it as an answer but I have no idea how. I'll probably do the correct calculations later on though.
RicardoTM
<the-moon><moon-phases><algorithm>
Is it possible to calculate the moon age from the phase angle?
RicardoTM
# Is it possible to calculate the moon age from the phase angle?

(Asked by: username_0 on 2024-12-21)

Given the phase angle of the moon (i) on degrees (0-360), is it possible to calculate its "age" in days?

**Tags:** the-moon, moon-phases, algorithm
> **Comments:**
> **username_1**: You could roughly approximate it by $ age=PA/360*29.5 $.  But the time taken to move a certain number of degrees isn't constant, so you need more information and a better algorithm for more accuracy.  
> **username_0**: @GregMiller I did try that however that approximation is not satisfactory. Is there another way to calculate it? My calculations are based on the book Astronomical Algorithms by Jean Meeus. I have everything calculated up to the illuminated fraction of the moon (k).  
> **username_1**: Here's a link to another approximation.  But if you can compute the phase, why not just compute the last new moon and count the days? https://www.celestialprogramming.com/snippets/moonage.html  
> **username_2**: @GregMiller: Nice snippet, but isn’t the precision a little “false advertising”? You should limit it to one or two decimals…  
> **username_0**: @GregMiller Because the process on the book is a little bit too much with 14 extra arguments + 25 corrections + another additional 14 corrections. Thank you, I'll try that method when I get on the PC later.  
> **username_1**: @PierrePaquette The decimals are required so the average is valid over a long range of time even though the individual predictions won't be accurate to that many decimals.  
> **username_0**: @GregMiller it works fine and way closer to the correct result. Thank you. I'd mark it as an answer but I have no idea how. I'll probably do the correct calculations later on though.  

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## 0 answers

