Why do hot days often see puddles in front of me?

The total reflex phenomenon causes pedestrians on a hot day to see illusions of objects like puddles.

On hot days, moving on the road people often see like puddles, or shadows of objects in front, but not close.

On 3-4 / 4, when going on the streets of Hanoi in the middle of the sun more than 40 degrees Celsius, many people have a feeling that there is puddle ahead.

According to Nguyen Duc Phuong (Hanoi National University), at that time the road surface (especially asphalt road) absorbed strong sunlight so it was very hot. This amount of heat then radiates back to heating the air layers on the road surface.

The more air the closer to the road surface is heated and will expand, the refractive index decreases. Therefore, light rays from a distant object such as cars and motorbikes will be refracted many times through air layers with different refractive index and tend to bend gently to the road surface. At some point the angle of incidence of the light ray that exceeds the value of the critical refraction angle will occur a total reflection .

Now light rays are reflected upwards and transmitted to the eye, making us see the looming shadow of the front object looming on the road. Along with that is the phenomenon of air convection that makes us feel like there is a puddle of water in the front and a flickering image.

The total reflection phenomenon also causes illusions in the desert.

• Wearing bright colored shirts will be cooler when going on a sunny day