Rare 'Four Moons' Phenomenon Dazzles St. Petersburg Sky

• Stargazers in St. Petersburg, Russia, witnessed a rare optical illusion of four moons, known as Paraselenae.
• Images of the spectacular phenomenon, also called moon dogs or mock moons, went viral on social media.
• Paraselenae are created when moonlight refracts through hexagonal ice crystals in high cirrus clouds.
• The phenomenon appears as bright spots flanking the actual Moon, typically at a 22-degree angle or more.
• They are easier to spot when the Moon is low, and their vertical extent depends on the size and wobbling of ice crystals.

Why It Matters: A rare atmospheric optical phenomenon, Paraselenae, created an illusion of four moons over St. Petersburg.