Sunrise and Sunset
Have we ever wondered that we actually see the sunrise about 2 minutes before the sun is actually at that perceived position? Did we ever know that the sunset that we actually see is of a sun that has already set? So why do these different perceptions occur? It is just because of a phenomenon that is termed as refraction of light.
What is refraction of light if we Simply put a light ray that ‘bends’ when it travels from one medium to another. Depending on the density of the various mediums the speed of the light which is traveling ray keeps varying and this causes it to speeded up or slow down therefore bending in the process takes place.
So how is this light refraction connected to our advanced sunrise and the delayed sunset? Imagine the situation or the journey of light rays from the sun. At first we shall see the journey of light is through vacuum and then through the atmosphere of the earth and then it is finally seen by us. At first, the vacuum which is present will act as a rarer medium and the earth’s atmosphere with all its temperature changes or winds and different gases will be denser in that medium in comparison to the same.
During the process of sunrise, the light rays bend due to our atmosphere and we see the sun early even though the sun is just below the horizon. Similarly at the time of sunset due to the same bending of light rays we can see the apparent position of the sun which is not the actual position.
By summing up all details which are due to refraction we can see or observe that the sun rises about two minutes before it’s actual time and sunset around two minutes later. even though it has already moved from its initial position.
Refraction
In physics, the process of refraction is the change in direction of a wave that is passing from one medium to another medium or from a gradual change in the medium. How much a wave is refracted is determined by the changes in wave speed and the initial direction of the wave which is propagating relative to the direction of change in speed.
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The refraction of light can be seen in many places in our day-to-day life. It makes objects under a water surface appear closer and clearer than they really are. It is the thing on which the optical lenses are based, allowing for instruments such as cameras, glasses, microscopes, binoculars and the human eye. Refraction is also responsible for some articles which are natural phenomena including mirages and rainbows.
Atmospheric Reflection
The air's refractive index depends on the air density and thus varies with the temperature of air and pressure as well. Since the pressure is lower than expected at higher altitudes, the refractive index that RI is also lower causes light rays to refract towards the surface of the earth when traveling long distances through the atmosphere. This whole process shifts the apparent positions of stars slightly when they are close to the horizon and makes the sun visible before it actually rises above the horizon during a sunrise.
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The temperature that varies in the air can also be the cause of the refraction of light. This can be seen as a haze of heat when cool and hot air is mixed over a fire in engine exhaust, or when opening a window on a very cold day. This makes objects viewed through the air which is mixed air and which appear to shimmer or move around randomly as the cold or hot air moves. This effect is also widely visible from normal variations in air temperature during a sunny day when using high magnification telephoto lenses and is often limiting the quality of the image quality in these cases. In a similar way the turbulence of the atmosphere gives rapidly varying distortions in the images of astronomical telescopes limiting the resolution of terrestrial telescopes but by not using adaptive optics or other techniques for overcoming these atmospheric distortions or the disorders.
Significance
The temperature of air variations that are close to the surface can give rise to other optical phenomena for examples such as mirages and Fata Morgana. This makes the road appear reflecting in nature by giving an illusion of water covering the road.
It is a clinical test in which a phoropter may be used by the appropriate eye care professional to determine the reflective error of the eye and the best corrective lenses to be prescribed.
FAQs on Advanced Sunrise and Delayed Sunset
1. What is the reason behind the Delayed sunset and Advanced sunrise?
The Advancement in sunrise and delayed sunset are the two phenomena that are caused due to the atmospheric refraction process. In this process the Sun appears to rise early by 2 minutes and set by 2 minutes late.
2. Why is the sun seen a few minutes before it actually rises while in the evening a few minutes longer after it sets?
From the sun When the rays of light enter the earth's atmosphere from outer space, they travel from a medium which is rarer medium to a denser medium.
3. What is the cause of apparent flattening of sun at Sunrise and Sunset?
The flattering of the sun at sunrise or sunset is due to refraction, because the sun becomes little visible a little before actual sunrise that remains visible a little after actual sunset that is because of the atmosphere's refraction process of light.
4. Why is the sunrise visible before the sun?
The sun rising is visible to us before the actual sunrise and after actual sunset because of the process of atmospheric refraction of light. The rays From the sun which are coming through space enter from the rarer medium to the denser medium and hence bend slightly towards normal at each refraction point and become visible to us before actual sunrise time.
5. What is the process of refraction like?
If we speak in terms of Physics, refraction is how a wave going through a gradual change in medium or passing from one medium to another, changes its direction. Changes in wave speed and the initial direction of the wave determines how much a wave is refracted. Even if we do not realize it, we see refraction in multiple places in our daily lives.
6. What is atmospheric reflection?
The quality of air constantly changes due to factors such as temperature, pressure and the presence of various gasses. Hence the air’s refractive index which is dependent on air density also changes. Pressure is lower at higher altitudes. Hence the refractive index which also lowers impacts the light rays traveling through long distances in the atmosphere and causes them to bend or refract as they hit earth’s surface. This process causes us to view apparent positions of stars on the horizon more than the actual ones and causes the phenomena of advanced sunrise and delayed sunset.
7. What are the other factors that can cause refraction?
Varying air temperatures also cause refraction. Examples of this can be seen when we open the window on a very cold day or observe the haze over the fire in an engine exhaust when cool and hot air mix with each other. Atmospheric turbulence also causes distortions in the images produced by astronomical telescopes. Hence the scope of terrestrial telescopes are limited. However, adaptive optics, lenses and other techniques can easily be used to try and overcome these atmospheric limitations. When we use a telephoto lens with high magnification, the effect of refraction can be observed when it produces limited image quality especially during a sunny day.
8. What are the applications of refraction?
Refraction is a key law of physics that is widely used in optics and new-age technology. In the past few years due to over-exposure to technology, the newer generations are experiencing issues in their vision. Refractive concave and convex glasses and lenses are used by the eye specialists to correct these errors in the human eye. Objects such as magnifying glasses, binoculars, lenses in projectors, peepholes in doors, etc also the principle of refraction. The most common example of refraction is a prism that refracts white light to form a beam of colors that we call VIBGYOR.
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9. What is the difference between reflection and refraction?
Reflection is the bouncing back of light rays when it hits a surface while refraction is the bending of light rays as it travels from one medium to another. In reflection, the angle of incidence of light is equal to the angle of reflections while in refraction it is not equal. Reflection occurs in mirrors and refraction is observed in lenses. In reflection the light returns in the same direction and in refraction the light changes direction as it travels between mediums. The speed of the light rays are more or less constant in reflection. With refraction it depends on the medium through which the light rays travel and get bent.
