Believe in the Impossible
As the saying goes, some things happen “only once in a Blue Moon”. In other words, hardly ever. Drawing this card suggests you’re about to get a rare chance, and that something “one-off” could well be about to happen. This card is a very positive sign if you’ve felt like you’re hoping for too much, or asking too much of the Universe. Whatever you are asking about - well, it might only happen once in a Blue Moon but it can happen! However, with this rare opportunity before you, it’s important that you believe in it. If you convince yourself that whatever you’re asking about can never go in your favor, then guess what? It won’t go in your favor! Be grateful for this card, which is a reminder to believe in your dreams.
Attune to the Moon:
There are usually three Full Moons between each equinox and solstice (and vice versa). Sometimes, though, we get four Full Moons in a single season. When this happens, the third of the season’s four Full Moons is called a Blue Moon - at least, that was the original definition of a Blue Moon. These days it’s popular to use the Blue Moon for the second Full Moon in any calendar month that has two Full Moons.
(Message directly from Guidebook)