My friend asked me
"Sun is also a star then why doesn't it twinkle like other stars"
I brought this question here so that I have (and have more) infomation on this topic.
Stars twinkle because they are effectively a point of light. This point of light can be distorted and magnified by movement of patches of varying density in the atmosphere. These act as lenses causing the twinkle effect. If you get to space, the stars don't twinkle. Stars appear as a point only because they are so very very distant.
Planets twinkle less because they appear as little discs of light. If one point is being made brighter by the atmosphere perhaps another is being made less bright. By being a disc, the twinkling is smoothed out by the average amount of light making it to your eye.
The sun is a very large disc because it is closer than the other stars. The sun is so large in the sky that the distortion of the light is not very noticeable. However when the sun is setting and its light has to travel through a lot more air to reach the ground, you will notice a shimmering around the edge. This is due to the same kind of atmospheric distortion.