It's a pet peeve of mine: I'm scrolling through Instagram images of landscape paintings and I see that an artist has decided to stick the moon in their painting. Only they do not understand the basic rules about where the moon realistically appears in the sky. Full moons, new moons, moons everywhere!
I was once guilty of this because I didn't know any better. My father gently pointed out to me that the new moon never appears opposite the sun: only above the setting sun.
I also frequently see artists stick a full moon in the same part of the sky as the sun. In reality, the full moon, when low near the horizon, is always opposite the sun. In the examples above, notice that the sun, not pictured, is behind the viewer, shining onto the cloud and rising full moon.
To inject a bit of humor here, I must admit that when it comes to art, anything goes. In my experience, many art-buying customers don't know whether the full moon you've painted is the moon or the sun! But if you wish your otherwise realistic landscape painting to read right, please take a moment to learn a little bit about your moons.