Why does the Moon look bigger near the horizon?
The Moon looks bigger near the horizon because of an optical illusion called the Moon illusion. Its actual size in the sky stays the same, as photos and measurements show.
When the Moon is near the horizon, your brain compares it with trees, buildings and landscape, which may make it seem larger. When it is high in the sky, there is nothing nearby to compare it with. Another explanation is that the brain perceives the sky as a flattened dome, so objects near the horizon seem farther away and therefore larger.
Scientists have studied the Moon illusion for more than 2,000 years, and there is still no single agreed explanation. You can test it yourself by holding a coin at arm's length or looking at the Moon upside down between your legs, which often makes the illusion disappear.
Real changes
The Moon's actual size in the sky does change slightly because its orbit is elliptical. At its closest point, during a supermoon, it can look about 14 percent larger than at its farthest. Near the horizon, it can also look orange or red because sunlight passes through more atmosphere.
Did You Know?
The same illusion makes the Sun and constellations look larger near the horizon.