ATMOSPHERIC

REFRACTION

ATMOSPHERIC REFRACTION

Atmospheric refraction is the deviation of light or other electromagnetic wave from a straight line as it passes through the atmosphere due to the variation in air density as a function of altitude.

This refraction is due to the velocity of light through decreasing with increasing density.

Refraction not only affects light rays but all electromagnetic radiation, although in varying degrees.

Atmospheric refraction becomes more sever when there are strong temperature gradients, and refraction and refraction is non uniform when the atmosphere is inhomogeneous, as when there is unbalance in the air.

This is the cause of twinkling of stars and various deformations of the shape of the sun at sunset and sunrise. So atmospheric refraction of the light from a star is zero in the zenith

Twinkling Of Stars Due to continuous atmospheric refraction of starlight.

Since the atmosphere bends straight towards the normal, the apparent position of the star is slightly different from its actual position.

The star appears slightly higher (above) than its actual position when viewed near the horizon.

This apparent position of the star is not stationary, but keeps on changing slightly, since the physical condition of the earth’s atmosphere are not stationary.

The apparent position of the star fluctnotes and the amount of star light entering the eye flickers-the star appears brighter as the path of rays of light coming from the star goes on varying slightly

The planets are much closer to the earth, and are thus seen as extended sources. If we consider a planet as a collection of a large no of point-sized sources of light. The phenomenon is termed terrestrial scintillation.

Atmospheric twinkling is defined as variations in illuminance only. Twinkling of stars is caused by the passing of light through different layers of a turbulent atmosphere.

Most scintillation effects are caused by anomalous refraction caused bye small scale fluctuations in air density usually related to temperature gradients.

Twinkling Of Stars

WHY DO NOT

TWINKLE ?

Planets do not Twinkle. Why ?Planets are very close to the earth as compared to the stars. The planets act as extended sources of light. So the intensity of light we receive from the planets is very large. Therefore, the variation in the brightness of the planets is not detected. Hence, planets do not twinkle.

ADVANCE SUNRISE &

DELAYED SUNSETSometimes the refraction of the light rays tend to being into view, objects which are actually below the horizon. This happens in the case of sun just before sunrise and just after sunset.

Thus, we can see the sun about 2 minutes before the sunrise and 2 minutes after the actual sunset because of atmospheric refraction. The actual sun rise takes pace when the sun is just above the horizon.

But due to refraction of sunlight caused by the atmosphere, we can see rising sun about 2minutes before it is actually above the horizon.

When the sun is slightly above the horizon then the sunlight coming from less dense air to more dense air is refracted downwards as it passes through the atmosphere.

Thus, the day would have been shorter by about 4 minutes if the earth had no atmosphere. The sun appears flattened at sunrise and sun set. The sun appears flattened at sunrise and sun set.

This apparent flattening of sun during sunrise and sunset is also due to atmospheric refraction.

It is also due to atmospheric refraction that we can still see the sun for about 2 minutes even after sun has set below the horizon. So, the time from sunrise to sunset is lengthened by 2+2=4 minutes because of atmospheric refraction.

Because of this atmospheric refraction, the sun appears to be raised above the horizon when actually it is slightly below the horizon.

ADVANCE SUNRISE &

DELAYED SUNSET

GROUP MEMBERSAkash Mahanand

Akash A.SAnandhu C.N

Aleena SureshAbhisha.R.Suresh