This question is a relatively easy question to answer in principle, but the mechanics behind can be a bit hard to describe and visualize. 

The moon has always been strongly associated with the night, just as the sun is associated with the day. This gets hammered home a lot in children’s books, and random imagery for day and night that gets passed around such as this:

The moon is the brightest object in the night sky on earth, but the moon is definitely not only visible at night.   The moon has a fairly complicated algorithm for when and where it is visible on earth.

So, when is the moon visible? To answer this, we need to understand how it’s moving.   The moon is circling the earth in its orbit, and is visible whenever it is on your side of the planet, and when some portion of the side facing earth is illuminated by the sun.  This relationship gets a little bit tricky because you have a lot of motion here.  Let’s break it down:

1. The earth is rotating on its own axis causing our day and night cycles.  One complete rotation in about 24 hours.
2. The earth (and moon) are moving around the sun and makes the entire trip around the sun in about 365 days.
3. The moon is revolving around the earth and makes one complete revolution approximately every 27.3 days. 

When you really think about it, that makes the whole system fairly complicated to visualize in terms of where things are and what is illuminated.  And that’s not even introducing the angle at which the moon is rotating compared to our orbit around the sun, tilt of the earth, the fact that the orbits are not perfectly spherical and several other factors that are going on.

The best way to visualize things is to make it so you can actually see it. So lets set it up in a 3d modeling program.  Please note that this is not to scale (not even close to scale… Space is really really big and to do this to scale, the earth and moon would just be dots or not visible at all).  This does not fully represent everything that is going on in the solar system or even with just the earth, sun and moon.  This is a simple representation of where the earth, moon and sun are, and how they are lit throughout a year.  This is viewed from above the sun, looking down on the system. 

So that’s a rough idea on how the things are moving and where the light is but we can’t see too much detail there so lets zoom in above earth:

The the earth is spinning really fast in this model so it’s a bit hard to tell where the moon would be visible but gives a good idea of how the earth and moon are illuminated throughout the year and how the moon is changing.  In the image above, one month goes by approximately every 2 seconds.  The image does show a full year of rotations which you can see by the changing angle of light on the earth and moon. Every rotation of the moon around the earth is about 28 days. 

To visualize this better we’re going to set up multiple cameras and take some snapshots.  I set up 4 cameras in the model.

• Camera 1:  Centered above the Sun.
• Camera 2: On the surface of the moon, at the center of the surface that is facing the earth.
• Camera 3: Centered above the earth.
• Camera 4:  On the surface of the earth at the center of the surface that is facing the moon.

I took a few random snapshots at different points throughout the year in the model.

Lets break down what these mean.

• Panel 1- Shows where the earth and moon are in relation to the sun as they travel around it.
• Panel 2- Shows what half of the earth will have the moon visible.  The portion of the earth that is dark will be seeing the moon at night, and the portion that is illuminated will see it during the day.
• Panel 3- Shows the earth/moon system, and where the moon is in relation to the earth and which portions are illuminated.
• Panel 4- Shows roughly what the moon will look like from the earth and what phase it is in.

Remember this is for a specific moment, not the entire day.  The moon will be staying at that point around the earth (relatively) for the whole day. The earth continues to rotate so the moon will be visible at most locations on earth as the earth rotates.

Lets look at another.

At this moment, the quarter moon would be visible to western Africa, Southern Europe, and some of South America and as the earth rotates, the moon seen in panel 4 would be visible to most locations on earth, each for a portion during the day, and a portion at night. 

Lets look at one more:

In this moment, the sliver of a moon would be visible to North and South America during the day. In this panel, since the earth is going to be rotating , the sliver moon will be visible at most locations on the planet, but it will be almost entirely during the day.

If you want to sit down and look at the 4 panel for any point I put it in a longer video format here:

The video still has the earth rotating very quickly, but that is because we compressed an entire trip around the sun (365 days) down to about 5 minutes, but it gives a really good idea on the motion and illumiation that is going on. 

The website Timeanddate.com has a great calculator which will tell you the time that the moon will rise, and set, for any time or date for any location.  It’s a great tool if you want to find out when the moon will be visible during the day or night.  They also have a column for “meridian passing” which works out to be “moon noon”.   Coincidentally they also have an application for sunrise and sunset for a given location at any time or date.

I did a quick calculation for June of 2018 viewing from New York, NY and found that the moon should be visible approximately 46% of the daylight hours in that month.  There was one day where the moon would be visible for the entire day.  Also for June in New York, there was no day where the moon was not visible at least for a few min while the sun was out.  The amount that it will be out and when will be change drastically month by month and location by location. 

I would definitely encourage you to look up your location and check to see when the moon is supposed to be visible during the day and go check it out yourself and do your own little experiment.  If you have questions don’t forget to ask a scientist.

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