Planets do not twinkle like stars because they are much closer to Earth and appear as tiny disks rather than point sources of light. The light from a planet covers a larger area in the sky, so the effects of atmospheric turbulence are averaged out over the planet’s apparent size. While some light rays might be refracted, others remain steady, making the overall light appear constant. This results in a steady shine rather than a twinkling effect.
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Understanding Why Planets Don’t Twinkle
Planets: Closer and Apparent Size
Unlike stars, planets in our solar system are much closer to Earth. This proximity means that they appear in the sky not as point sources of light, like distant stars, but as tiny disks.
The Effect of Atmospheric Turbulence on Planets
When light from planets passes through Earth’s atmosphere, it encounters the same turbulence that causes stars to twinkle. However, the effect on planets is different due to their apparent size in the sky.
Averaging Out the Atmospheric Effects
The larger apparent size of planets means that the light reaching us covers a broader area in the sky. As a result, the atmospheric turbulence affects different parts of the light differently. Some rays might be refracted, but others remain steady.
The Steady Shine of Planets
This averaging effect of the different light rays means that the overall light from a planet tends to remain constant in our view. While individual rays of light are still impacted by atmospheric changes, their collective impact averages out, resulting in a steady shine.
Contrast with Stars
In contrast, stars are so far away that they appear as mere points of light. The atmospheric turbulence affects all the light from a star in the same way, leading to the noticeable twinkling effect.
Planetary Stability in the Night Sky
Therefore, the lack of twinkling in planets can be attributed to their relative proximity to Earth and their larger apparent size, which allows the effects of atmospheric turbulence to be averaged out, presenting a steady light to observers on Earth.