Elapsed time from the preceding new Moon
The relevant new Moon is the phase-longitude-zero instant immediately before the requested UTC instant. Subtracting that timestamp from the requested timestamp gives the duration in 24-hour days.
Adjacent phase results use strict time ordering: previous is earlier, next is later, and the selected instant stays between them.
Why phase angle is not a clock
The mean synodic month is 29.530588853 days, but individual lunations vary. Orbital speed changes and the Sun-Moon geometry evolves, so phase angle divided by 360 and multiplied by the mean month does not consistently equal the elapsed duration.
A submitted wall-clock time becomes one UTC instant through its named zone. Changing only the display zone leaves lunar age unchanged; changing the actual instant changes both the preceding-new-Moon relationship and the elapsed duration.
Worked example
Worked lunar-age example
At 26 August 2026, 12:00 UTC, the preceding new Moon and elapsed interval are:
- Previous new Moon
- 12 August 2026, 17:37:11 UTC
- Selected instant
- 26 August 2026, 12:00:00 UTC
- Elapsed lunar age
- 13.766 days
- Phase direction
- waxing
The elapsed value comes from timestamp subtraction rather than multiplying the 160.5012-degree phase angle by a constant. The next new Moon does not define the age at this instant.
Read before comparing
Reference conditions
- Age is reported in uniform 24-hour days from UTC instants, not in local calendar-day boundaries.
- Here, new Moon means the geocentric principal phase at zero degrees, distinct from the first locally visible crescent.
- A rounded age should not be used to reconstruct a new-Moon timestamp; use the reported adjacent event instead.
Next step
Use the working calculator
Calculate another exact instant with the same reference frame and conventions described on this working sheet.