Twinkling stars on a warm summer night are incredibly romantic. The answer to the question, why do stars twinkle, is simple. The stars shine very calmly in space, and they only twinkle because bubbles of warm air in the Earth’s atmosphere deflect the light from the star differently again and again.
Why Do Stars Twinkle?
The light of the stars in the night sky has to travel distances of tens of billions of kilometres to reach us. It runs through the space between the stars and planets practically unhindered. But if the light reaches the Earth’s atmosphere, its smooth run is over.
The air currents and bubbles of air deflect the light beam. Since the bubbles are often only a few meters in size and move quickly, the light deflection is always different in a fraction of a second.
The star twinkles and seems to flicker when seen from Earth, but it shines evenly for astronauts on the International Space Station.
Why Do Stars Twinkle But Not Planets?
The air bubbles not only change the brightness of the star but also its position in the sky. The image of the star in the sky moves back and forth. Some points of light in the night sky do not come from distant fixed stars, but planets in our solar system.
They are so close to the Earth that, in contrast to the stars, they cannot be recognized as points, but on closer inspection as tiny disks. The brightness fluctuations are less visible on a bright surface than on a tiny point of light.
Since far more light comes from the bright planets in the solar system, the twinkle is only noticeable when the air is extremely unstable. Stars and planets can usually be easily distinguished in the sky because stars twinkle and planets do not.
So if you see a bright point of light at night that barely sparkles, you are most likely looking at a planet.
High Tech Telescopes That Correct The Twinkle Effect
Even at the best locations on Earth, the twinkling of the stars is so strong that it ultimately limits the performance of the telescopes. The top telescopes on Earth could theoretically see everything much sharper, but the wavering air envelope in the atmosphere doesn’t allow this to happen.
Only telescopes in space, such as the Hubble telescope, always see extremely sharply, since the starlight does not have to go through an annoying atmosphere.
To eliminate interference from the atmosphere, astronomers have been using the so-called adaptive optics technology for several years. The telescope analyzes the dancing image of a star in the field of vision.
Based on this data, the shape of a moving mirror in the beam’s path changes up to 1000 times per second in order to correct the disturbances in the air envelope. This technology is used in the Very Large Telescope (VLT) of the European astronomy organization (ESO) in Chile.
The technologically advanced telescope in the Atacama desert looks almost as sharp as if it were in space.
Why Do Stars Twinkle, But The Sun Does Not?
The observed brightness of a celestial body is always linked to three main factors that are distance, luminosity and size. This is evident from the star that brightens our sky, the sun. It is also the only star that we can immediately see as a disc with the naked eye.
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The sun is much closer to us than the other stars. The amount of light the Earth receives from the sun is very high. So, even if the air bubbles deflect and change the path of some of the light beams, there is plenty of light to cover up the overall deflection. That is the reason why do stars twinkle, and the sun does not.
The question, why do stars twinkle, must be clear now. There are other reasons we look towards the stars for, like for the dream of reaching the stars one day. Setting up a colony and expanding human civilization.