Moon out during the day
The moon out during the day is ordinary: it spends roughly half of each day above the horizon and can be seen in a blue sky on most days. The surprise it gives says more about our habits than about the sky.
What it may mean
The moon is above the horizon about half of every day, so it spends as many hours in daylight as in darkness, and on most days it can be found somewhere in a blue sky. It still surprises people, a pale chip of chalk over a parking lot at noon. A saying collected in 1903 had fun with that: no one but a rascal can see the moon in the daytime, which, the book added, is an indirect way of saying that each of us is a bit of a rascal now and then. Small faults behave like the daytime moon. Most people assume theirs are rare and well hidden (the snapping before coffee, the borrowed pen never returned, the email answered with half a mind), when nearly everyone around them has the same ones in plain view. Admitting them out loud makes them smaller.
Depending on how you saw it
A half moon in the afternoon
At first quarter, a half moon rises around noon and hangs in the eastern sky all afternoon, its lit side facing west toward the sun. Half of it is always dark from where you stand. Which half of a story have you been seeing, and where is the light coming from?
Sun and moon in the sky together
On many mornings and afternoons you can see the sun and the moon at once, and the bright edge of the moon points straight at the sun that lights it. The shape stops being a mystery. What puzzle in your life becomes simple once you see the cause and the result side by side?
A full moon setting at sunrise
On the morning after a full moon, the moon sinks in the west just as the sun comes up in the east, and for a few minutes both sit on opposite horizons. What in your life is ending just as something else begins?
Why it happens in nature
The moon rises and sets about 50 minutes later each day and is above the horizon for roughly half of every day, so it is often up in daylight. It is easiest to see in a blue sky in the afternoon around first quarter and in the morning around last quarter. Near new moon it sits too close to the sun to spot, and a full moon rises only as the sun sets.
To reflect on
Which small fault of yours turns out to be one nearly everyone around you shares?