Why the 'Supermoon' Will Look Largest Near the Horizon

For reasons still unknown to science, the moon appears much larger and more magnificent when it is near the horizon than when it is soaring overhead, despite the fact that the moon's size never actually changes.

One possible explanation holds that we're used to seeing clouds just a few miles above us, but we also know that clouds on the horizon can be tens of miles distant. If a cloud on the horizon appears the same size as a cloud overhead, we can infer that the cloud on the horizon, because of its greater distance from us, must be huge. And because the moon near the horizon is the same size as it normally is overhead, our brains automatically tack on a similar enlargement. 

 

But not everyone thinks clouds have worked their magic on our brains to such a great extent. There are a few alternative hypotheses; one holds that the moon seems bigger near the horizon because we can compare its size to nearby trees and other objects on Earth — and it looms large in comparison. Overhead, amid the vast expanse of outer space, our lone satellite seems diminutive.