Just saw and managed to snap a beautiful 22 degree moon halo. They are caused by the moon’s light refracting through the ice crystals in the high clouds.
In this case the clouds almost certainly thin cirrostratus clouds which are presaging the arrival of bad weather. Halos are not the same as moonbows, although they are often called that in error.
The same phenomenon is just as common around the sun. My thanks to Eddie Fast (great name) for sending this example seen above Singapore: