Just imagine that the water is swirling and moving in every direction. The straw would then appear and disapear. It would twinkle.
Now replace the straw with a star and the water with an athmosphere :)Read more
If you observe the sky at night to gaze for stars you have to look through the earth's atmosphere. Due to turbulences (e.g wind) and rapid temperature changes (due to pressure changes, boyancy etc.) in it, the refraction index of the air changes over time and space. Imagine that each small air parcel in the athmosphere is acting like a lense which is also moving, therefore the incoming light is... Read more