If you look up at the stars at night, then you might think the stars flicker, blink, wink, or twinkle. You might ask yourself, “why do the stars appear to twinkle?” While you may think that the stars are twinkling, they actually are shining steadily. They only appear to twinkle because of the interaction between your eyes, the starlight, and the Earth’s atmosphere.
The Earth’s atmosphere is made up of different levels of temperatures and densities. In addition to the temperature and density differences, there is a lot of wind in the atmosphere. When the star’s light enters the Earth’s atmosphere, it must pass through these layers of temperature differences, density differences, and wind. Moving air in the atmosphere can be called turbulence.
The star’s light must enter our atmosphere, but the star’s light does not necessarily move in a straight line thought the atmosphere. Instead, the starlight is refracted, or is spread around in different directions in the atmosphere. The starlight becomes bent as it moves towards the Earth. As the light disperses, or spreads, the star’s brightness changes, causing us to see the star “twinkle.” Additionally, as the bent starlight reaches us, the star also twinkles. The two effects of atmosphere on the light causes us to see a twinkle. However, you should remember that the star itself is not twinkling. The bending and spreading of light only makes you think it is twinkling.
If the atmosphere on a particular night is windier or the temperatures are severe, then the stars might appear to twinkle more than on milder and calmer nights.
Stars twinkle more than planets, as planets usually do not appear to twinkle. Stars look much smaller in our sky because they are further away from Earth. Planets are much bigger in size and closer to Earth in location, so there is more light passing through our atmosphere. The size of the planet, and the light coming from it, reduces the amount light disturbed by the Earth’s atmosphere.
If you were to travel beyond the Earth’s atmosphere, or if you were to take the place of an astronaut for a day, then you would see that the stars shine steadily. There is no atmospheric disturbance in space, so the stars do not appear to twinkle when observed beyond the Earth’s atmosphere. The telescopes we send into space take better pictures of stars than telescopes on Earth because the telescopes in space do not have to take pictures through our disturbing atmosphere. For the telescopes on the ground, scientists use lasers and mirrors to adjust to the star’s twinkling, which creates a clearer picture of distant stars.
Stars appear to twinkle to us on Earth because our planet’s atmosphere contains wind, temperature differences, and density variation. As the light from a distant star passes through our chaotic atmosphere, the light spreads out and becomes bend. The bending and spreading of starlight as it reaches our eyes causes us see twinkling stars.
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