Why do planets exhibit a much steadier light compared to stars during observation?

Planets appear as tiny discs, unlike stars which are pinpoints distorted by Earth's atmosphere.

The difference in perceived steadiness between planets and stars is rooted in how their light interacts with Earth's atmosphere. Stars twinkle because they are perceived as single pinpoints of light; as that narrow beam passes through the atmosphere's turbulence, the light path is easily distorted, causing the perceived brightness and position to fluctuate rapidly. Planets, conversely, are much closer to Earth, appearing as tiny discs rather than pinpoints. This larger apparent size means the atmospheric distortion affects different parts of the disc simultaneously, resulting in a much steadier, un-twinkling light that observers can rely on for detail.