Question

A star appears slightly higher (above) than its actual position in the sky. Illustrate .​

Answer 1

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We know that the gradual change in the refractive index of different layers of the atmosphere due to the varying conditions of it causes atmospheric refraction. When starlight enters the atmosphere, it gets refracted continuously. The higher level of air acts as a rarer medium while the dense air near the surface of earth acts as a denser medium. So, the atmosphere bends the starlight towards the normal. As a result, the apparent position of star is slightly different from its actual position. Thus, star appears slightly higher (above) than its actual position in the sky.

Answer 2

The bending of the light when it passes from one medium to another, like water to air, or one layer of air to another, is called refraction. Refraction is what makes a straw look bent when you put it in a glass of water.

Light from a star is refracted (bent) as it leaves space (a vacuum) and enters the earth's atmosphere. Air higher up in the sky is rarer but that nearer the earth's surface is denser. So, as the light from a star comes down, the dense air bends the light more. Due to this refraction of star's light, the star appears to be at a higher position. For example,  through the actual position of a star is at A, but due to atmospheric refraction, it seems higher in the sky at position B (This is because our eye will see the star at that position from where light enters it in the straight line direction). Our nearest star, the Sun, also seems higher than it actually is, due to atmospheric refraction.