The Moon appears so big tonight mainly due to an optical phenomenon called the "Moon illusion," which makes the Moon look larger when it is near the horizon compared to when it is high in the sky. This illusion happens because the brain misinterprets the size of the Moon based on its surroundings—when the Moon is near the horizon, it is seen next to familiar objects like trees and buildings, which tricks the brain into perceiving the Moon as much bigger. Additionally, if the Moon is near its closest point to Earth in its orbit (called perigee), it can be actually slightly larger in appearance, known as a "Supermoon".
Key points:
- The Moon illusion is a psychological effect tied to perception and context.
- The Moon's actual angular size does not significantly change as it moves across the sky.
- Occasionally, the Moon is physically closer to Earth at perigee, making it appear about 14% bigger—a Supermoon.
- The Moon near the horizon may also appear colored (yellow or orange) due to atmospheric scattering, but this does not affect its perceived size.
So, the Moon looks especially big tonight likely because it is either near the horizon or it is a Supermoon, or both combined.
