Does the moment of the full moon come every same number of days?
The moon phase chart tells us how the moon phase needs real period correction.
If you want to ask a friend to see the full moon, you can't just add a fixed month length to "the last full moon". The movement of the moon is not uniform. The original book first estimates the average time, and then adds multiple sets of period corrections to find the new moon, first quarter, full moon and last quarter respectively.
Guess first
Is the time between each full moon strictly equal to 29.530588861 days?
Show answer and explanation
No, this is the average month length — The actual moon phase moment is also affected by the periodic changes in the movement of the moon and the sun.
Then connect experience and science
First explain which moon phase
The moon phase moment is defined by the difference in elongated longitude between the sun and the moon at the center of the earth. The new moon is 0°, the first quarter is 90°, the full moon is 180°, and the last quarter is 270°. It does not require that the three celestial bodies are exactly collinear.
The moon phase moment is a clear geometric condition
The average monthly length is just the starting point
The new moon near the year 2000 is used as the starting point for numbering. Use integers, one-quarter, one-half or three-quarters of k for different phases.
Average time: 29.530588861 k plus polynomial
plus complete major period terms
New moon/full moon/quarter moon have their own corrections; quarter moon also adds and subtracts W, and all phases add 14 compensations.
True time = average time + phase correction + additional correction
Then decide whether you can see it locally
The full moon moment is a time label for the same event around the world, but whether it can be seen on that day and at what time depends on the time zone, rise and fall, and weather.
TT date is not local clock time
k uses the synodic moon as the counting unit, and integers plus 0.25, 0.5, and 0.75 correspond to the four phases respectively. Calculate the average JDE first, then add the moon phase-specific periodic terms and additional terms; you cannot just use a fixed 29.53 days to extrapolate the precise time.
give it a try
Compare the four moon phases in the same period, or click on the original book for examples of new moon in 1977 and last quarter in 2044. Use TT for the date, not the clock time in your location.
No need to memorize symbols
- k
- Moon phase event number, step size is 1/4
- JDE / TT
- Dynamic time consecutive days / Earth time
- M / M′ / F
- Solar periapsis angle/lunar periapsis angle/lunar latitude parameters
- W
- Additional correction for upper and lower chords with opposite signs
Algorithm, accuracy and scope of application
Realizes 49.1 average time and all major periodic items of 49.A, including 25 new moon items, 25 full moon items, and 25 quarter moon items; E/E² factor, upper/lower quarter ±W and 14 additional compensation items. k Negative numbers use the correct non-negative fractional part; non-quarter integers are explicitly rejected. Passed the original book 49.a/b and AA+ multi-phase/positive and negative k comparison. This lesson estimates nearby numbers by year, non-real-time "next time" query, and does not include UTC leap seconds/ΔT or local fluctuations.
my understanding check
Does a lunar eclipse necessarily occur when a full moon occurs?
uncertain — A full moon is a 180° difference in ecliptic longitude; the moon may also deviate from the ecliptic plane and does not have to enter the earth's shadow.
In this chapter, what does the 0.25 part of k represent?
winding — The whole number is the new moon, +.25 first quarter, +.5 full moon, +.75 last quarter.
Can the TT time of the full moon be output directly as the local time on your home calendar?
cannot — It is also necessary to convert the time scale and time zone, and check whether the local area is above the horizon.
The moon phase moment requires geometric events, and the average moon length is just the starting point; the same event and seeing it locally are two different things.
Jean Meeus · Astronomical Algorithms, 2nd ed. · No. 49 chapter