The Moon looks so big tonight due to a combination of two main factors: the Moon illusion and the supermoon phenomenon. The Moon illusion is an optical effect where the Moon appears larger near the horizon than when it is high in the sky. This happens because our brains compare the Moon to terrestrial objects like buildings and trees, making it seem larger than it really is. The supermoon occurs when the full Moon is at or near its closest point to Earth in its elliptical orbit (called perigee), making it appear up to 14% larger and about 30% brighter than when it is farther away (at apogee). When a supermoon coincides with the Moon being low on the horizon, the Moon can appear particularly huge and bright, creating a breathtaking sight.
In other words, tonight's big Moon appearance is due to it being a supermoon and the optical illusion the human brain creates when viewing the Moon near the horizon.
