- Twinkling of stars is due to atmospheric refraction of starlight.
- The starlight undergoes refraction continuously when it enters the atmosphere.
- The atmosphere has different media of different refractive index.
- During refraction the starlight bends towards the normal.
- Due to refraction by different media the apparent position of the star is different from its actual position.
- The stars are very distant and they act as point-sized sources of light.
- The physical conditions of earth’s atmosphere are not stationary.
- Thus the apparent position of the star fluctuates.
- The star sometime appears brighter and sometimes later fainter. This is called twinkling effect of a star.
- Planets are not twinkling because they are much closer to the earth.