Question

Name the phenomenon due to which the stars seem higher in the sky than they actually are.

Answer 1

Because of refraction in the earth's atmosphere: The air density in the earth's atmosphere and therefore also the index of refraction of the earth's atmosphere decrease with increasing altitude. Snellius' law of refraction tells us that light is refracted towards the medium with higher index of refraction. Therefore, the light coming from any star that is not situated directly above the observer takes a curved path bent down towards the observer, arriving at the observer at a steeper angle than had it travelled on a straight line.

Due to atmospheric refraction, the stars seem to be higher in the sky than they actually are. This can be explained as follows : 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, in figure, 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.