The illusion of a pool of water on the roadway is actually a reflection of the sky in the moist air layers on the road. The moisture in the air around us always looks like liquid to our eyes because this is what we are used to seeing.
The horizon line in the distance is where the sky and water meet. Because light travels faster than sound, everything beyond this line will appear blurry due to the presence of air bubbles between you and these objects.
This effect can be seen in large bodies of water such as oceans or lakes but it can also be found in smaller puddles on streets or in parking lots during rainstorms.
It is important to remember that this is only an optical trick so do not rely on your eye's ability to deceive you. If there is actually any danger present, stay put!
What exactly do we perceive when we witness a "water on the road" mirage on a hot day? Light from distant objects is refracted into your eye, giving the illusion of a reflection, which we perceive as water on the road. Blue light is scattered more than any other color by gas molecules in the environment. When you look at clouds or even plain old glass, you are seeing blue light scattered by particles in the atmosphere.
The sun's rays are bent away from the earth by the atmosphere and travel through space until they hit something else to bend their path. This happens whenever you look up at the sky on a sunny day: The sunlight must pass through space before it reaches your eye, so some of it is deflected toward the horizon. This is why near mountains you often find yourself looking down instead of up at the sky.
Scattered light from an object will eventually reach someone if they are looking in its general direction. If you are on foot, you will probably not notice this effect because things that scatter light tend to be far away. But if you are riding in a car, distant objects with bright colors will appear to flicker in and out of view as you drive by them. This is because red, orange, and yellow objects will seem to jump around when viewed from a distance, while green trees and brown hills remain still.
The flickering sensation is strongest for red objects and disappears for blue ones.
Why does the road reflect light in the same way as puddles of water do? You've probably surmised that the sight of artificial water on the road ahead is a mirage, and you'd be right. It's the same phenomenon that happens when folks in the desert mistakenly believe they see water on a nearby sand dune. Refraction is the cause of this reflecting illusion. As light travels through air it bends or refracts depending on how it is traveling (straight vs. curved). This means that when light hits an object with a different density than air it will bend around the object. On a bright day when there are no clouds in the sky, people seeing mirages often report that they can also see straight down the road as far as the eye can see. This is because any objects that are further away don't affect their view so much; instead, what affects their view is anything closer than halfway between their eye and the object being seen.
The image below shows why this occurs. Imagine that we are looking at the scene from above, with the sun shining down on the road and dust particles floating in the air. The light from the sun has many paths it could take, but since there is nothing to interrupt its path, it would reach the horizon directly back towards the sun. However, due to refraction, part of this light always reaches the dust particle first, and is reflected back up towards the earth. When this light encounters another dust particle it will be reflected too, and so on.
Because the air just above the road is hotter, light rays from the sky bend and end up aimed towards your pupils in the event of "water on the road." As a result, you can't see the road ahead and instead perceive wavy splotches of reflecting surface instead of what appears to be pools of water. This is called heat haze.
The sun's rays are absorbed by any particles in the atmosphere (such as dust or moisture) causing them to heat up. As these particles rise into the air, they emit that heat laterally, forming a hot wind or "heat wave". The resulting thermal gradient between the warm air close to the ground and the cooler air high up in the atmosphere gives rise to a pattern of bright and dark lines across the landscape known as "heat waves".
Heat waves come in two varieties: direct and indirect. Direct heat waves occur when sunlight directly strikes the surface, such as during a sunny day. Indirect heat waves happen when solar radiation is scattered by particles in the atmosphere, such as dust or moisture, causing it to heat up and rise before finally being deposited somewhere else. For example, when clouds pass over a desert area during midday, this scattering of light causes an increase in temperature throughout the cloud layer. As the heat rises, it evaporates any liquid present (such as rain or dew), forming large droplets that scatter light even more and thus creating an indirect heat wave.
Light travels (is refracted differently) at varying temperatures of air, generating the waviness you perceive and giving the appearance that the road is wet. This causes the air to bend light differently near the road's surface, resulting in a refraction of the sky. This effect is called thermal radiation.
Bending light is what gives glass its shiny appearance; it is also what allows sunlight through windows during the day and provides heat during cold nights. Light is also bent when it passes through water, which is why lights are placed high up on buildings as not to be seen from below. The higher the light, the less likely it is to be bent by water molecules.
The sun's rays are reflected off all the objects surrounding you when you walk outside; this includes cars, trees, buildings... The more reflective an object is, the more likely it is to reflect some of the sun's energy back into space. Non-reflective objects such as asphalt or sand only allow light to pass through them. As far as we know, light cannot be absorbed so it must either be reflected or passed on. When it reaches an object with no possible way to reflect it back, it continues on its path until it hits something else or is stopped by the atmosphere.
Atmospheric gases such as oxygen and nitrogen have molecules with electrons that can be shared with other atoms or molecules.
Why can you see your reflection in a pool of calm water? Light slows down when it reaches the water, and some of it reflects. The part that doesn't get reflected is visible because it's behind the surface. For example, if you were to walk up to a still pond and look into its center, you would see your image there.
This effect is called "refraction" and happens whenever light travels through a medium (in this case, air or water) that has different properties from light. For example, if you were to drive a car across the Canadian border into New York State, you would notice that the windshield was clearer outside than inside the car. This is because there's more open space between the glass and the vehicle outside than inside; thus less light gets trapped within the glass.
Reflection also occurs when light hits an object with a flat surface. Some of the light will be reflected back toward the source while another part will go straight ahead. If the object that the light is hitting is transparent, such as glass, only light waves that travel at the same speed as the wave that created them will be reflected back. Wavy surfaces within the object, such as those found on clouds or trees, will reflect both forward and backward moving waves. These reflections add color to the scene before us.