What is the Moon Illusion? Why Does the Moon Look Really Big?The Moon illusion makes the Moon appear much larger when it is closer to the horizon. Find out what causes the illusion in this article.
Why does the Moon appear so large when it rises or sets? This trick our brains play on us is the Moon illusion. Photographs prove that the Moon is the same size near the horizon as high in the sky, yet this is not what the human eye perceives. As a result, it is an optical illusion caused by how our brains absorb visual information.
The Moon, despite its apparent enlargement on the horizon, remains the same size. This intriguing phenomenon, known as the "Moon illusion", has captivated minds since ancient times. Its presence is most pronounced during a full Moon, when the maximum area of its disc is illuminated. The Moon illusion, a concept first documented by Aristotle in the 4th century BC, continues to fascinate us today.
In reality, the Moon has roughly the same apparent diameter of around half a degree, whether or not it is looming over the horizon or riding high in the sky. One reason behind the Moon illusion arises from our perception of the celestial sphere above us; instead of a hemisphere, we perceive the sky as shaped like a flattened dome. Consequently, the lower the Moon is in the sky, the further away and bigger it is perceived to be; when the Moon is high in the sky, we perceive it to be nearer to us and subsequently smaller in apparent size.
A few people appear to be immune to the Moon illusion, even though the viewer may be fully aware that there is no appreciable difference in the Moon's apparent diameter for any given evening, irrespective of its height above the horizon.
The Moon Is More Yellow Near the Horizon
When the Moon is low in the sky, it undergoes a significant colour change. It takes on a more yellow or orange hue compared to its appearance when it is high overhead. This change is a result of the Moon's light traversing a greater distance through the atmosphere. As the light travels, more of the shorter, bluer wavelengths are scattered, leaving behind a higher concentration of the longer, redder wavelengths. The presence of dust or pollution in the atmosphere can further enhance this yellow and orange colouration.
The Harvest Moon is the most famous example of a large, golden-yellow Moon. However, any time the Moon is near the horizon, it will appear larger and orange.
