Why Do The Stars Twinkle?

Have you ever looked up at the night sky and wondered, why do the stars twinkle as they do? The stars appear to twinkle as they reflect light from the sun. Light travels at 186,282 miles per second (299,792 km/sec) through space.

When light hits something, such as a star or planet, some of its energy gets absorbed and reflected out into space.

Why Do The Stars Twinkle

This happens because the atoms in the object absorb certain wavelengths of light and then reemit them at longer wavelengths.

This phenomenon is called Rayleigh scattering, and it also explains why the sky looks blue. We look at this phenomenon in closer detail and work out exactly why stars twinkle and shine bright as they do.

How Does A Star Form?

Stars are formed when massive clouds of gas collapse under their gravity. As this occurs, the temperature rises until hydrogen becomes ionized. At this point, electrons become stripped off of the protons in the hydrogen atom.

Once this occurs, the matter can no longer support itself against gravity and collapses inward on itself.

As the cloud collapses, the heat generated by gravitational contraction causes the material to begin radiating energy outward. This process continues until the mass reaches about 10 solar masses.

At this point, nuclear fusion begins within the core. Nuclear fusion converts hydrogen nuclei into helium nuclei, releasing tremendous amounts of energy.

When the star has reached the main sequence stage, it will have expanded enough to fuse carbon into oxygen.

After this, the star will continue burning heavier elements like nitrogen, silicon, magnesium, iron, etc., converting these elements into helium. Eventually, all of the remaining heavy elements will be converted into helium.

Why Do The Stars Appear To Twinkle?

This might sound odd, but on a technical level, stars do not twinkle, but they appear to twinkle when they are looked at from the Earth’s surface.

The stars that we see twinkling when we are stargazing are a result of how light is reflected in our atmosphere. When starlight enters our atmosphere, it becomes affected by the winds as well as areas with varying densities and temperatures.

This means the light from the star twinkles when you are looking at the stars from the ground. But what causes this light?

Stars appear to twinkle because of two things: diffraction and refraction. Diffraction simply means that the light waves spread out as they travel through an aperture.

Refraction is the bending of light due to changes in density. Both of these phenomena cause the starlight to disperse as it passes through the atmosphere.


The first thing that causes the starlight to spread out is the fact that the air molecules act like tiny lenses. These lenses focus the light rays onto each other and create interference patterns.

The size of the lens depends on the wavelength of the light being observed.

The smaller the wavelength, the larger the lens. For example, red light is much shorter than green light. Therefore, the lenses for red light are much bigger than those for the green light. In addition, the distance between the lenses is also greater.

If you were standing next to a window, you would see a very fine pattern of lines if you looked at the sun. That’s because the sun’s light is made up of many wavelengths. Each line represents one wavelength. The closer you look, the more lines you see.

If you took a picture of the sun using a camera with a long exposure time (like 30 seconds), you would see hundreds or even thousands of lines. This is called diffraction and relates to starlight too.


The second reason why stars seem to twinkle is because of the change in the density of the atmosphere. Light travels faster in dense regions than in less dense ones. This is known as refraction.

As the light moves toward the observer, the speed increases. Because the density decreases, the light bends away from the normal path. So instead of moving straight down, the light curves around and eventually hits the observer.

To understand how this works, let’s consider a glass bottle filled with water. If you put your finger inside the bottle, you can feel the pressure difference. As the water rises above your finger, the pressure decreases.

When light travels through the atmosphere, there are places where the air is thin and others where the air is thick. This creates a gradient in density. The higher the density, the slower the light travels. The lower the density, the faster the light travels.

Different parts of the atmosphere have different densities. Air near the top has a low density while air near the bottom has a high density. This makes the light curve around and hit the observer.

So why does all this matter? It matters because it affects the appearance of objects. Objects that are close to the observer will be seen as brighter than objects farther away.

This is especially true for stars. Since stars are so far away, they are small compared to the diameter of the Earth. They appear to move across the sky because the atmosphere acts like a giant lens.

This effect is most noticeable when looking closely at a star. When you get close, the image appears to jump back and forth. This is called parallax.


The third reason why stars twinkle is due to the movement of the Earth. The Earth rotates once every 24 hours. This means that the stars never stay still. Instead, they travel across the night sky.

If you watch the stars carefully, you’ll notice that some move slowly while others move quickly. Some move in an arc while others move in circles. These movements are caused by the rotation of the Earth.

Why Do The Stars Twinkle

Why Do Planets Not Twinkle?

Stars twinkle while planets do not because stars are so far away from earth. Despite this mind-blowing distance, it actually makes stars seem more prominent in the night sky.

This is because they appear as striking, concentrated points of light in the black wash. This small, insanely distant pinprick of light is then more disturbed by the effects of the Earth’s atmosphere, amounting to the signature twinkle of the stars.

Planets are a lot closer, and the sunlight that gets reflected comes back through Earth’s atmosphere yet in a thicker beam of light that is not as affected by the effects of the atmosphere.

Planets don’t twinkle and are found along the ecliptic. This should therefore help you distinguish between a star or a planet when looking up at the night sky.

If it looks like it’s performing some sort of frantic optical Morse code, it’s a star, and if it’s emitting a roughly steady light, it’s a planet you’re peepin’!

Final Thoughts

We hope after reading this article, you now know why stars twinkle. For a lot of people, the concept is romantic and stargazing can be a fun activity for everyone.

But remember, stars do not twinkle, but the way the light reflects and passes through our atmosphere makes it seem like they do! Keep stargazing, and keep exploring space, there’s so much more than stars to discover out there!

Gordon Watts