About to ask a novice ass question LOL. If todays moonphase is a full moon for example, does that mean this evening will be a full moon, or was last evenings the full moon??
In one sense, neither:
one of the four phases of the moon, occurring when the earth lies between the sun and the moon so that the moon is visible as a fully illuminated disc[/quote]
So, the true full moon occurs at that specific moment, which sites like timeanddate.com will tell you for your location, and you can either do the rit at that time, or slightly before it (for the just-still-technically waxing moon) or slightly after, for the just-beginning-to-wane moon.
But it won’t occur at midnight, for example, or at a specific same time of day each time, because lunar cycles are not exactly 28 days to the minute.
Go read the science pages about this, NASA probably have some entry level stuff explaining the whole topic.
(Flat earth disclaimer because I know some people have that idea, the time shown will still be accurate, midway between specific points of waxing and waning, so whatever, no need to pile in here! )
Like Lady Eva said, it changes every month. Last month, for example, the moon became full just before midnight, but was still full the following evening up to a point, so that is when I worked. It not so much a “what day to what day?” thing so much as it is a “what time to what time on what days?” thing.
If the full moon occurs tonight, yesterday’s and tomorrow’s moons are also full. You get three full moons. And that teaching is old and works.