If you look at the starry sky at night in clear weather, you will notice how some stars twinkle and even change their color. For example, the star Sirius from the constellation Canis Major, which is one of the brightest in the sky, literally shimmers with all the colors of the rainbow. This is an incredibly beautiful phenomenon, but why does it happen? And even more interesting, why do some objects flicker while others don’t? For example, the Sun, which is also a star, does not twinkle, and neither do the Moon and other planets. Moreover, looking into the night sky, you can see many stars that shine with an even, constant light.
Many stars in the sky twinkle and even change color. Photo source: sputnik-abkhazia.ru
Why do stars change brightness
Many objects in space are actually not exactly the same as we see them. Including the twinkling of stars, which can often be observed from Earth, has nothing to do with the stars themselves. The thing is that the atmosphere separates us from space. It seems absolutely transparent and stable, but in fact the atmosphere is mobile and resembles laminated, wavy glass.
When light passes through this heterogeneous “glass,” it is refracted many times. Moreover, these refractions are unstable due to several factors that cause flicker. One of them — this is turbulence. The air in the atmosphere is constantly in motion. For example, when solar energy heats the air, warm currents rise and mix with cold air.
Sirius, one of the brightest stars in the sky, often twinkles and shimmers in different colors. Photo source: earthsky.org
In addition, air currents collide with mountains and break into many swirling currents. All this causes turbulence, that is, turbulence in the atmosphere that is constantly in motion. By the way, for the same reason, planes sometimes fall into “air holes” during flight, which we talked about earlier.
Another reason for flickering is due to density differences between different layers of the atmosphere. Moreover, the density is also not constant. Accordingly, as mentioned above, the refractive index of air is not constant. When light passes through different media, it undergoes a tiny deflection each time, which is perceived by our eyes as flicker.
For this reason, scientists install professional telescopes only in certain places where the atmosphere has minimal influence on the light of cosmic objects. As you might guess, such places are mountains.
Telescopes are installed in the mountains to minimize the influence of the atmosphere. Photo source: www.dw.com
Why do stars change color
The change in the color of stars is associated with the same reasons as flickering. As you know, they shine with all the colors of the rainbow. However, the atmosphere serves as a kind of light filter, that is, it suppresses part of the spectrum of electromagnetic radiation. For example, it is for this reason that the Sun appears yellow to us, although in fact it is white.
At the same time, the atmosphere is unstable. Accordingly, the absorption of electromagnetic radiation also occurs inconsistently. This is what makes the stars, or rather the light that reaches the retina of our eyes, shimmer in different colors.
Why do some stars not blink
So, we have figured out the twinkling and color change of stars. But why do some stars twinkle intensely, others barely noticeably, and others do not twinkle at all? The thing is that the intensity of the twinkling depends on several different factors. One of them is the visible diameter of the light source – the smaller the diameter, the stronger the twinkling. For this reason, the Sun and planets, which can be observed with an amateur telescope, do not twinkle.
The sun does not flicker because it is close and emits bright light. Photo source: iguides.ru
Another important factor is the wavelength of light. If it is short, then the light is refracted more strongly, resulting in more intense flickering. For example, stars with a red glow, such as Antares from the constellation Scorpius, twinkle less intensely than blue ones, such as the aforementioned star Sirius.
In addition, the twinkling is more intense when viewed with the naked eye, since The average pupil diameter is 6 mm, which means that not much light is captured. If you look at the star through a lens that collects a wider beam of light, the flickering will be weak or not at all, but the image will become blurrier.
The intensity of the twinkling depends on the position of the star in the sky. Photo source: universemagazine.com
Another important factor is the position of the star in the sky. The greater the distance that light has to travel through the atmosphere to reach the eye, the more twinkling the star will appear. This is because the light is more affected by turbulence and other atmospheric processes that cause flickering. Accordingly, the closer a star is to the horizon, the more it flickers, since the light travels tangentially, that is, it travels a long distance through the atmosphere.
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It must be said that even in different weather the stars twinkle differently. For example, when humidity is high, when density is high, stars twinkle more strongly because there are stronger vibrations in the air.