<p>I did the same math using Excel: 12/15/2024 21:02 UTC - 1262*29.530588 = 12/4/1922 6:35 UTC.</p>
<p>That would be 6:35 am, not pm.</p>
<p>Depending on what time zone you are in, the link to <a href="https://www.calendar-12.com/moon_phases/1922" rel="nofollow noreferrer">Calendar-12.com</a> may be showing times based on your local time zone. For me, it comes up in the time zone for America/New York. 6:24 am Eastern time = 11:24 UTC.
<a href="https://i.sstatic.net/51iNLtJH.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/51iNLtJH.png" alt="from Calendar-12.com showing the Moon phases in 1922" /></a></p>
<p>11:24 UTC agrees with <a href="https://aa.usno.navy.mil/calculated/moon/phases?date=1922-12-01&amp;nump=25&amp;format=p&amp;submit=Get%20Data" rel="nofollow noreferrer">U.S Naval Observatory</a> calculation of 11:23 UTC.
<a href="https://i.sstatic.net/TTUP8kJj.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/TTUP8kJj.png" alt="from U.S. Naval Observatory showing the Moon phases in Dec 1922" /></a></p>
<p>The difference of 5 hours between 6:35 UTC (our calculation) and 11:23 UTC (U.S. Naval Observatory) is because the synodic period of 29.530588 is the average over a long time. The synodic period from month to month does vary by several hours from the mean. A difference of 5 hours is within that variation.</p>

CC BY-SA 4.0
2024-11-26T16:02:31.820Z
2024-11-26T16:02:31.820Z
JohnHoltz
<p>According to NASA the next full moon is on December 15, 2024 at 9:02 pm UCT, JDN 2460659.875. Lunation zero is 1262 lunations earlier.  NASA'S value of 1 synodic month is</p>
<p>S = 29.530588 days</p>
<p>I wanted to know the time of day of the full moon of December 1922, and I performed the following calculation:</p>
<p>2460659.875 - 1262×29.530588 = 2423392.272.</p>
<p>That's about 30 minutes after 6:00 pm.</p>
<p>My problem is, I checked this <a href="https://www.calendar-12.com/moon_phases/1922" rel="nofollow noreferrer">site</a>, and it has the December 1922 full moon on December 4, 1922 at 6:24 am.  So my question is what time of day was the full moon of lunation zero?</p>

CC BY-SA 4.0
2024-11-25T18:09:33.270Z
According to Chapront (2002) the *mean* synodic month at the epoch J2000.0 is ~29.530588861 days, but the actual synodic month length varies from that in a complex way, as I explain in https://astronomy.stackexchange.com/a/55112/16685 You can use the mean value to *estimate* the time between lunations, but you need much more complex calculations to get the precise time.
PM 2Ring
CC BY-SA 4.0
2024-11-25T18:21:00.947Z
From JPL Horizons, there was a Full Moon on 1922-Dec-04 11:23:17.554 UT = JDN 2423392.974508728, with the Sun at ecliptic longitude 251.5408784, latitude -0.0000928 °, and the Moon at long 71.5408784°, lat -4.8445811° (geocentric).
PM 2Ring
<observational-astronomy><moon-phases>
What time of day was the full moon of lunation zero?
lee pappas
# What time of day was the full moon of lunation zero?

(Asked by: username_0 on 2024-11-25)

According to NASA the next full moon is on December 15, 2024 at 9:02 pm UCT, JDN 2460659.875. Lunation zero is 1262 lunations earlier. NASA'S value of 1 synodic month is

S = 29.530588 days

I wanted to know the time of day of the full moon of December 1922, and I performed the following calculation:

2460659.875 - 1262×29.530588 = 2423392.272.

That's about 30 minutes after 6:00 pm.

My problem is, I checked this [site](https://www.calendar-12.com/moon_phases/1922), and it has the December 1922 full moon on December 4, 1922 at 6:24 am. So my question is what time of day was the full moon of lunation zero?

**Tags:** observational-astronomy, moon-phases
> **Comments:**
> **username_1**: According to Chapront (2002) the *mean* synodic month at the epoch J2000.0 is ~29.530588861 days, but the actual synodic month length varies from that in a complex way, as I explain in https://astronomy.stackexchange.com/a/55112/16685 You can use the mean value to *estimate* the time between lunations, but you need much more complex calculations to get the precise time.  
> **username_1**: From JPL Horizons, there was a Full Moon on 1922-Dec-04 11:23:17.554 UT = JDN 2423392.974508728, with the Sun at ecliptic longitude 251.5408784, latitude -0.0000928 °, and the Moon at long 71.5408784°, lat -4.8445811° (geocentric).  

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## 1 answers

### Answer by username_2 on 2024-11-26. Score: 2

I did the same math using Excel: 12/15/2024 21:02 UTC - 1262\*29.530588 = 12/4/1922 6:35 UTC.

That would be 6:35 am, not pm.

Depending on what time zone you are in, the link to [Calendar-12.com](https://www.calendar-12.com/moon_phases/1922) may be showing times based on your local time zone. For me, it comes up in the time zone for America/New York. 6:24 am Eastern time = 11:24 UTC.
[![from Calendar-12.com showing the Moon phases in 1922](https://i.sstatic.net/51iNLtJH.png)](https://i.sstatic.net/51iNLtJH.png)

11:24 UTC agrees with [U.S Naval Observatory](https://aa.usno.navy.mil/calculated/moon/phases?date=1922-12-01&nump=25&format=p&submit=Get%20Data) calculation of 11:23 UTC.
[![from U.S. Naval Observatory showing the Moon phases in Dec 1922](https://i.sstatic.net/TTUP8kJj.png)](https://i.sstatic.net/TTUP8kJj.png)

The difference of 5 hours between 6:35 UTC (our calculation) and 11:23 UTC (U.S. Naval Observatory) is because the synodic period of 29.530588 is the average over a long time. The synodic period from month to month does vary by several hours from the mean. A difference of 5 hours is within that variation.


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