A circle round the moon means rain. In some localities the number of stars inside the circle denotes the number of days until it will rain.
Prince Edward Island; general in the United States.

A circle round the moon means rain. In some localities the number of stars inside the circle denotes the number of days until it will rain.
Source: Current Superstitions (1896), entry 996.
Fanny D. Bergen, editor.
Prince Edward Island · United States
Modern normalized navigation; the historical attribution above remains unchanged.