Astronomy
Phase fraction
Turns the age into a position in the cycle. Zero is new moon, 0.25 is first quarter, 0.5 is full moon and 1 is the next new moon.
The Formula
f = age / 29.530588853
Turns the age into a position in the cycle. Zero is new moon, 0.25 is first quarter, 0.5 is full moon and 1 is the next new moon.
| Symbol | Meaning | Unit | Notes |
|---|---|---|---|
| age | Moon age | days | Days since the last new moon. |
| f | Phase fraction | dimensionless | Position in the cycle, from 0 to 1. |
What Each Symbol Means
agedays
Moon age
Days since the last new moon.
fdimensionless
Phase fraction
Position in the cycle, from 0 to 1.
See It Worked With Real Numbers
A formula on its own does not tell you which number goes where. The how to calculate the moon phase page applies this equation to a concrete case, shows every intermediate step, and names the mistakes that produce a wrong answer even when the algebra is right.
Where This Formula Appears
This equation is the working core of How To Calculate The Moon Phase, filed under Science. Every number the guide produces comes from substituting into this one line.