Test: Atmospheric Refraction

The stars seem to be higher in the sky than they actually are due to atmospheric refraction.

As the light rays from a star pass through the different layers of atmosphere (density of layers increasing downwards), they suffer atmospheric refraction from a rarer to a denser medium. So they bend towards the naormal at each layer. Due to continuous refraction, the light from the star appears to come from a point which is actually higher than the star.

The cooler air layers of the atmosphere behave as optically denser medium for light rays whereas the warmer air layers (or hotter air layers) of the atmosphere behave as optically rarer medium for the light rays. So, in the same atmosphere we have air layers having different optical densities. And when light rays pass through the atmosphere having air layers of different optical densities, then refraction of light takes place.

We can see the sun 2 minutes before the actual sunrise and 2 minutes after the actual sunset due to atmospheric refraction. So, the total time lengthened is 2 + 2 = 4 minutes.

Due to the atmospheric refraction, we can see the sun 2 minutes before and after actual sunrise and sunset. The rays of light emitted by the sun are refracted towards the ground while travelling through the optically rarer layers of air in the atmosphere; when the Sun is slightly below the horizon. This results in making the sun appear slightly raised above the horizon and hence the sun is visible 2 minutes before and after actual sunrise and sunset.

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. By actual sunrise, we mean the actual crossing of the horizon by the Sun. Fig. shows the actual and apparent positions of the Sun with respect to the horizon. The time difference between actual sunset and the apparent sunset is about 2 minutes. The apparent flattening of the Sun’s disc at sunrise and sunset is also due to the same phenomenon.

Advanced sunrise and delayed sunset : The sunrise is advanced due to atmospheric refraction of sunlight. An observer on the earth sees the sun two minutes before the sun reaches the horizon. A ray of sunlight entering the earth's atmosphere follows a curved path due to atmosphere refraction before reaching the earth.

To an observer on Earth the stars appear to twinkle. This is due to the fluctuation of physical conditions in the earth’s atmosphere.  Each single stream of starlight is refracted and is caused to change direction. This is because the light which passes the different layers of atmosphere differ in temperature and density. This causes the light from the star to twinkle when seen from the ground.

The light rays pass through greater thickness of air because of which the light rays from the lower side of the sun are retracted more than those from the upper side. Because of unequal light bending, the sun looks oval and larger. 

The deviation of the light or electromagnetic wave due to the variations in the air density as the function of the height when the light or the wave passes through the atmosphere is known as atmospheric refraction.

When light rays from stars enter the earth atmosphere it travels from space which vacuum ( rarer) into earth atmosphere which is denser.