Why stars flicker whereas planets shine steadily?

“Twinkle, twinkle, little, star,” says the famous lullaby. Aside from wondering what they are, have you also thought why stars flicker whereas planets steadily shine?

While you might think that starts blinks, winks, or twinkle when we gaze at them at night, they are actually shining consistently or unwaveringly. They only seem to flicker because of the three different factors, the atmosphere of the Earth, the starlight, and your eyes.

The Earth’s atmosphere is composed of various layers, from the innermost troposphere to the outermost exosphere. Each has its own characteristics and different level of density and temperature. Plus, it also has moving air or wind, which causes turbulence.

Now, as the starlight reaches Earth, it passes through these different layers, densities, temperature, and turbulence. Instead of traveling through a straight line, the gleam is fanned out or refracted in different directions. Thus, causing it also to bend as it moves towards the Earth’s surface.

When light spreads or disperses, it alters the brightness of the starlight, making it seems that stars twinkle as we gaze them. Meanwhile, the bending of the light as it reaches us also contributes to the flickering effect. Keep in mind that the star itself isn’t blinking, but the atmosphere effect on its light makes the difference. If there is no atmosphere, then we would see stars shining unwaveringly as there is no element to alter its stream of light.

Meanwhile, turbulence also adds up to the flickering effect. You might notice that the stars tend to twinkle more on windier nights as compared to milder ones. Rough nights may also make stars seems that they are shifting in position as more considerable turbulence causes more intense refraction of light, seemingly like watching a coin dance at sinks at the bottom of a river or pool.

But why do planets tend to shine steadily? Well, it boils to the distance of these heavenly bodies. The planets in our solar system are far closer to Earth compared to the stars we see at night. With that, planets tend to appear larger and transmit thicker beams of light, reducing the effects of turbulence and the Earth’s atmosphere and eliminating the twinkling effect they cause on starlight. To put simply, diffractions of light cancel out, and the effects of the atmosphere become negligible.

The said scenario can also apply to starts themselves. If you take a closer look, you might notice that other stars twinkle more compared to other stars. That is because stars also vary in distance. The closer the star, the less it shimmers. The farther it is, the more it blinks.

Astronomers on Earth uses adaptive optical devices to combat the stars’ flickering effect. The tools they use consists of many small mirrors, which continuously adjust to the atmospheric disturbances. However, for astronauts on space, they see stars shining steadily. That is because there are no atmospheric disturbances and turbulence that can affect starlight and force it to twinkle.

Telescopes we have on space can also get better images of stars than those telescopes we have on Earth. Space-based telescopes escape the problems caused by our complex atmosphere. Meanwhile, Earth-based telescopes are equipped with mirrors and lasers that can adjust to disturbances, allowing us to obtain quite clearer photographs of faraway stars.

More Readings:

Star (Wikipedia)

Planet (Wikipedia)

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