Have you looked at those sparkling stars and asked yourself, why do stars twinkle?  Well, it is mostly a question asked during childhood. For a child, it’s a fascinating natural phenomenon that feels magical. But behind the magical twinkling lies a scientific explanation. In this post, we’ll go through the science behind this beautiful flickering light show. Let’s begin!

What Makes Stars Twinkle?

The short answer is – the Earth’s atmosphere causes star looks twinkly. In detail, as the light from stars travels across space and enters our atmosphere, it passes through several layers of air. These air layers vary in temperature and density. This condition is called atmospheric turbulence.

Due to atmospheric turbulence, the star’s light refracts or bends multiple times before reaching our eyes. As a result, the position of the star appears to move slightly. This slight movement makes the star seem like it is twinkling. Therefore, that twinkle you see is the light from stars being distorted by our planet’s atmosphere.

Light Refraction is the Key to Twinkling

Light refraction is the main cause of the twinkling behavior of a star. You may recall back the science experiment that you did in school where the spoon/rod/pencil bent underwater. Both the experiment’s observation and the star’s twinkling behavior are caused by light refraction.

Light refraction is a physics concept for how light bends when it passes through different materials. In the case of stars, the material causing this bending is our very own atmosphere. The air closer to the Earth’s surface is denser and often warmer, while the air higher up is cooler and thinner. This mix creates a constantly shifting atmosphere. Therefore, the bending process isn’t constant. As a result, the light from the stars appears to flicker or twinkle when it finally reaches your eyes.

Another way to visualize this phenomenon is by imagining sitting at the bottom of a swimming pool and looking up at a distant object outside the pool, like a tree. The water distorts the light coming from that tree, so the tree appears to shift or wobble. Now, apply that same concept to the star’s light, except instead of water, its Earth’s atmosphere causes the distortion.

The Colors of Twinkling Stars

If you’ve ever looked closely at stars, you might have noticed that sometimes they appear to flicker in different colors, especially those twinkling near the horizon. This phenomenon is also caused by the refraction process.

Sometimes, stars seem to shimmer between hues of red, blue, or even green. This phenomenon occurs because starlight, much like sunlight, is made up of all the colors in the visible spectrum. Each color corresponds to a different wavelength, and these wavelengths behave differently when passing through the atmosphere.

As starlight gets closer to the Earth’s surface, the thicker layers of the atmosphere scatter the light in different wavelengths, sometimes producing a range of colors. So, if you ever see a star twinkling and changing color, it’s the atmosphere distorting the star’s light even more dramatically.

There are two physics concepts applied to the phenomenon of the stars changing color. To further understand the process behind this phenomenon, you can refer to this post.

Does Weather Affect How Stars Twinkle?

The twinkling effect changes depending on weather conditions, and where you are observing the stars. On clear nights with calm air, stars will twinkle less. While, on windy or humid nights, the stars will flicker more because the atmosphere is more turbulent.

You’ll also notice less twinkling if you’re stargazing from high altitudes or places with thin air, like a mountain or desert. This is because there’s less atmosphere for the starlight to pass through, meaning less refraction and less twinkling.

Summary

The twinkling stars are not just a magical sight but a result of the starlight refraction in Earth’s atmosphere. As starlight passes through layers of air with varying temperatures and densities, it bends and shifts. Therefore, creating the flickering effect we observe. Factors like atmospheric turbulence, weather conditions, and even altitude can impact how much stars twinkle. The atmosphere also causes stars to shimmer in different colors. Next time you look up at those twinkling stars, you’ll know that there’s more to that sparkle than meets the eye!