🌕 That's a Moiré
A Moiré pattern is an interference pattern produced by overlaying similar but slightly offset templates. A simple example is obtained by taking two identical ruled transparent sheets of plastic, superposing them, and rotating one about its center as the other is held fixed.
Such a neat little phenomena. I had to whip up a little example I could play with.
Be careful, these examples can be disorienting, so proceed with caution.