The Sun appears larger at sunrise and sunset due to the atmospheric refraction effect. When the Sun is close to the horizon, its rays of light pass through a greater thickness of atmosphere, causing an apparent distortion of its size.
When you look at the Sun at sunrise or sunset, your brain can be deceived by an illusion called the Moon illusion. It is simply an amplified perception, due to the surrounding context: near the horizon, your gaze automatically incorporates elements like buildings, trees, or mountains into your visual field. Your brain compares, assesses the proportions, and convinces your eyes that the Sun is larger, while its actual apparent size does not change at all. On the contrary, when it is high in the sky, with nothing around for comparison, it appears smaller. Our brain is quite skilled at rearranging what it perceives, and that's how it makes us believe unreliable things.
When the Sun is low on the horizon, its rays must pass through a much thicker layer of air than during the day. This layer acts like a kind of lens, a phenomenon known as atmospheric refraction. Thanks to this phenomenon, light is slightly bent downward, creating the illusion that the Sun is higher than it actually is. As a result, we perceive a somewhat distorted and flattened image of the Sun. Although refraction doesn't ultimately enlarge the Sun much, it enhances the impression that it appears larger during sunrise or sunset, especially when combined with other optical or psychological phenomena.
Atmospheric particles such as dust, humidity, or pollutants influence the way we perceive the sun at sunrise and sunset. When sunlight passes through more atmosphere near the horizon, it encounters more of these small particles. They scatter the light waves, especially those with shorter wavelengths, such as blue. As a result, it’s mainly the red and orange waves, which are less scattered and disturbed, that continue their journey to us. The result: the sun takes on a bright orange or reddish hue, appearing larger and more spectacular to our eyes. Moreover, this scattering, known as Rayleigh scattering, is responsible for those fiery skies that make morning or evening photos so beautiful on Instagram.
Our brain judges the size of objects based on the immediate visual context. When the Sun is close to the horizon, it appears surrounded by familiar elements (trees, mountains, buildings). This context influences our perception, making the Sun seem larger. In contrast, high in the sky, without nearby reference points, it appears isolated and thus seems smaller. This phenomenon is known as the Ponzo illusion, an optical illusion where two identical objects appear different due to the context surrounding them. Our brain regularly falls into this trap, and the Sun is no exception.
Did you know that the Moon also appears much larger on the horizon for the same optical and psychological reasons as the Sun? This phenomenon is called the lunar illusion.
Did you know that in reality, the Sun appears slightly smaller when it is near the horizon? Atmospheric refraction actually compresses its vertical shape, giving it a slightly flattened appearance rather than a perfectly round one.
Did you know that when the Sun is near the horizon, the light passes through a much thicker layer of atmosphere than during the day? This additional thickness explains why red, orange, and pink colors dominate at sunrise and sunset.
Did you know that the illusion that makes the Sun look larger on the horizon is called the Ponzo illusion? This illusion uses visual cues from the landscape to trick our brain into perceiving the actual size of celestial objects incorrectly.
During sunrise and sunset, sunlight passes through a greater amount of the Earth's atmosphere. This scatters the shorter wavelengths (blue and green), mainly allowing the red and orange wavelengths to reach our eyes.
Yes, atmospheric particles from pollution or dust increase light scattering, which can intensify red or orange hues and influence our perception of the apparent size and brightness of the Sun.
Yes, this phenomenon is also observed with the Moon (lunar illusion). It often appears larger when it is near the horizon, for similar reasons involving visual perspective and environmental context.
Even close to the horizon, directly observing the Sun can be harmful. Although the intensity of light is reduced by the atmosphere, the ultraviolet rays present can still permanently damage the retina. It is recommended to always use appropriate eye protection.
No, the actual size of the Sun does not change. This phenomenon is due to an optical illusion called the 'moon illusion,' related to visual perspective and environmental context that alters our perception.
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