The planets being much closer to Earth are seen as extended sources. If we consider a planet as a collection of a large number of point-sized sources of light, the total variation in the amount of light entering our eyes from all these individual point-sized sources will average out to zero. This averaging effect nullifies the twinkling phenomenon.
How does the proximity of planets to Earth contribute to the absence of the twinkling effect?
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The absence of the twinkling effect for planets is influenced by their proximity to Earth. Unlike distant stars, planets appear as extended disks due to their relatively close distance. This larger apparent size makes them act as extended sources of light, averaging out the atmospheric turbulence effects. The scattered light from the planetary disk results in a steadier illumination. Additionally, the planets’ proximity minimizes the impact of Earth’s atmosphere on their perceived brightness, reducing the fluctuations in light intensity. Overall, the combination of their disk-like appearance and closer proximity contributes to the absence of the twinkling effect when observing planets.
Apparent Size of the Light Source:
Stars, being distant point sources of light, are more susceptible to atmospheric turbulence. The light from a single point on a star’s surface can be significantly affected by the Earth’s atmosphere, causing the twinkling effect.
Planets, on the other hand, appear as disks rather than points of light when observed from Earth. The apparent size of the planet is larger compared to individual stars. This extended nature of the light source helps to average out the effects of atmospheric turbulence. The overall brightness is a combination of light from different parts of the planet’s surface, contributing to a more stable and less twinkling appearance.
Distance from Earth:
Planets in our solar system are much closer to Earth compared to most stars. The distance to a celestial object affects how much its light is influenced by the Earth’s atmosphere.
Light from stars has to traverse a longer path through the Earth’s atmosphere, encountering more atmospheric layers and variations in density. This longer path increases the likelihood of atmospheric turbulence, leading to a more pronounced twinkling effect.
Planets, being closer, have a shorter path through the atmosphere. The reduced atmospheric path minimizes the impact of turbulence on the observed light, contributing to the reduced or absent twinkling effect.
In summary, the combination of the apparent size of the light source and the proximity of planets to Earth results in a more stable and less twinkling appearance compared to distant stars. The extended nature of the light source and the shorter atmospheric path contribute to this effect, making planets appear as steady, non-twinkling points of light in the night sky.