[Physics Class Notes] on Advanced Sunrise and Delayed Sunset Pdf for Exam

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.