Atmospheric Refraction – Wavering or Flickering

In summer days, during afternoon, we can see apparent, random wavering on the hot road. This is because, hot air forms rarer medium, whereas, cool air forms denser medium. However, when light rays originate form object and pases through hot air, thereby, undergoing refraction. Since , air is not stationary, thus apparent positions of object fluctuates thereby, causing wavering or flickering. Thus it is result of atmospheric refraction.

Atmospheric Refraction – Twinkling of stars

During night, stars in the sky appears to change its brightness i.e. sometimes they appears bright whereas, sometimes they appear to be faint. Such an effect is called as twinkling of stars. Star is present at large distance from earth. Thus it is a point source. Light travelling from the star undergo refraction in Earth’s Atmosphere. Since, light travelling from rarer medium or vacuum to denser medium or air, therefore, light ray bends towards normal. Therefore, the apparent position of star slightly above the actual position. However, air is not stationary,and temperature also varies, thus the refractive index of air changes continuously. Due to which when the atmosphere refracts less light towards us then the star looks faint. However, when atmosphere refracts more light towards us then star appears to be bright. This phenomena is called twinkling of light.

Planets do not twinkle

As compared to star, planets are much closer to earth. Thus planets are not point source. Large number of rays are emitted from planets. These rays undergo different refraction but these are not observable since, these nullify each others effect. Thus the average intensity remains constant. Hence, planets did not twinkle.

Atmospheric Refraction – Advance sunrise and Delayed sunset

Sunrise is crossing the sun above horizon and sunset means crossing of sun below horizon. Rays from sun follow a curved path, due to refraction in earth’s atmosphere. Thus, sun is visible two minutes before the actual sunrise and two minutes after the sunset. This is how, duration of day is increased by four minutes
Keywords: Wavering, Flickering, Twinkling of stars, Horizon