![]() Scattering of light is the deviation of light rays from its straight path. As light propagates through the atmosphere, it travels in a straight path until it is obstructed by bits of dust or gas molecules.ĭuring sunrise and sunset, the sun is at the horizon and refractive index of the atmosphere of the earth decrease with height. The apparent flattening of the Sun's disc at sunrise and sunset is also due to the same phenomenon. The time difference between actual sunset and the apparent sunset is about 2 minutes. By actual sunrise, we mean the actual crossing of the horizon by the Sun. The Sun is visible to us about 2 minutes before the actual sunrise, and about 2 minutes after the actual sunset because of atmospheric refraction. This is apparent sunrise.Īpparent sunset occurs slightly later than the actual sunset, since the light from the sun is already below the horizon, it refracts through the atmosphere, enabling us to see the apparent sunset, even after the sun has already set. The refracted rays reach the earth making it appear as if the sun has already risen above the horizon. When the sun is just below the horizon, its rays enter earth’s atmosphere and are refracted towards the earth. Further, this apparent position of the star is not stationary, but keeps on changing slightly, since the physical conditions of the earth's atmosphere are not stationary. The star appears slightly higher (above) than its actual position when viewed near the horizon. Since, the atmosphere bends starlight towards the normal, the apparent position of the star is slightly different from its actual position. The atmospheric refraction occurs in a medium of gradually changing refractive index. The light of stars, after entering the earth's atmosphere, undergoes refraction continuously before it reaches the earth. ![]() In scientific terms, the twinkling of stars is termed as astronomical scintillation. Because of this, the light rays when pass through various layers of atmosphere gets deviated. Atmosphere is composed of layers of various optical densities. The order of colours in a rainbow is popularly identified using the acronym, VIBGYOR, each letter standing for a colour in order.Ītmospheric refraction refers to the apparent random wavering or flickering of objects due to inconsistency in the physical conditions of the refracting media such as air. Light disperses and creates a rainbow effect, when it propagates and refracts in a prism.The splitting of white light into its constituent colours is called dispersion of light.The angle between the directions of the incident ray and that of the emergent ray is called the angle of deviation and is represented by Greek letter δ or q d. ![]() The angle between the normal and the refracted ray is known as the angle of refraction. The angle formed between the incident ray and the normal at the point of incidence is known as the angle of incidence. The ray that deviates at the point of incidence due to a change in the medium is the refracted ray. The angle between two refracting surfaces of a triangular glass prism is denoted by A, called the angle of the prism or the refracting angle. ![]() Any two rectangular faces are the refracting surfaces and the third one is the base. It is a solid structure having three rectangular and two triangular surfaces. This phenomenon can be observed in a lab environment using a triangular glass prism. The wavelength of each colour is different that causes the difference in velocity of the corresponding light when passing from one medium to another. The cause of dispersion is that sun light consists of seven constituents (colours namely violet, indigo, blue, green, yellow, orange and red popularly referred to as VIBGYOR) that have different refractive index with respect to a medium. Rainbow is the natural phenomenon in which dispersion takes place.
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