HIGHLIGHTS
- One theory states that depth perception plays an important role in how we see the moon on the horizon.
- Mathematician and astronomer Claudius Ptolemy explained the Moon illusion by atmospheric refraction.
- According to the “gaze angle” hypothesis, the moon illusion is produced by changes in the position of the eyes in the head accompanying changes in the elevation angle of the Moon
You have probably noticed many times how the
You actually witnessed a natural phenomenon
The moon illusion makes the moon appear larger near the horizon than it does higher in the sky. Although it has been known since antiquity and recorded by various cultures, the phenomenon is still debated.
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Here are all the possible explanations:
Depth perception and depth cues
One theory states that depth perception plays an important role in how we see the moon on the horizon. We see the moon on the horizon in the presence of depth cues such as mountains, trees, seas and other landscapes. And as the moon moves higher in the sky, the depth cues disappear.
For this reason, we see the moon farther on the horizon than when we see it high in the sky.
Refraction and distance
Mathematician and astronomer Claudius Ptolemy explained the Moon illusion by atmospheric refraction, which is the deflection of light or other electromagnetic waves from a straight line as it passes through the atmosphere.
Later he explained that it happened because of the apparent distance.
Gaze angle hypothesis
The Moon illusion is produced by changes in the position of the eyes in the head accompanying changes in the elevation angle of the Moon, according to the “gaze angle” hypothesis.
Once popular, this theory has been debunked by many experts.

Color
The moon appears to be red and larger during harvest season for those living in rural areas. The effect is created when the sky is clouded with dust and other particles.
Visual and atmospheric factors
The moon appears larger on the horizon when it is polluted, hazy, or smoky outside. The illusion may seem clearer after a forest fire or a pollution episode in a city.
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