Of course, when you look at the night sky, you can see the billions of stars that make up the universe. One of the curiosities that stars have, unlike planets and other moons, is that they twinkle. That is, it seems that they are constantly flashing. Many people wonder why the stars shine and the planets don’t.
Why do stars shine?
Everything outside the atmosphere flickers (yes, that includes the sun, moon, and planets in our solar system). This effect occurs when starlight interacts with air masses. In our case, this air mass is the atmosphere, which is full of turbulence. This causes the light to be constantly refracted in different ways, so the starlight is at one point on the surface from our vantage point, and after a few milliseconds, it changes slightly.
Why do we not notice the twinkling of the planets, the sun and the moon? It is easy to explain. Because of our distance from them (the nearest star, Proxima Centauri, is only 4 light years away), these stars appear to us as mere points of light. Since only a point of light penetrates the atmosphere, it can be greatly affected by air turbulence and therefore continues to flicker. In addition to being closer, the planets appear as discs (though not to the naked eye), which makes the light more stable (whereas the Moon and Sun are much larger, so the effect is imperceptible).
Some stars seem to change color
Some days around midnight, the quintuple star (one of the brightest stars we can see in the sky) is above the horizon (N-NE direction), but close enough to appear to be twinkling as well. A variety of colors (red, blue, green…). This is a fairly common phenomenon that is easily observed in stars near the horizon, but can also be seen in other stars.
The explanation is the same as for twinkling, but we add that the amount of air through which the light has to pass to us is much greater, so the refraction is more pronounced, which also produces stars that constantly change color. Also, although they don’t usually twinkle, planets can also emit this changing light if they are too close to the horizon.
How to avoid flashing
Although the twinkling of stars does not mean any kind of inconvenience to us, for astronomers things can change a lot. We have many observatories on the surface of the earth, so we have to remove this distortion to see the stars. To do this, some of the most advanced telescopes on Earth use adaptive optics, turning the telescope’s mirrors many times per second to compensate for turbulence in the atmosphere.
Astronomers project a laser into the sky, creating an artificial star in the telescope’s field of view. Now that you know what you want the artificial star to look like and what color, all you have to do is adjust the mirror distortion with the piston to eliminate the effects of atmospheric distortion. It’s not as efficient as launching a telescope into space, but it’s much cheaper and seems to serve our needs well.
Another option, as you can see, is to launch the telescope directly into space. Without the interference of the atmosphere, the flash disappears completely. Perhaps the two most famous space telescopes are Hubble and Kepler.
In size, Hubble is much smaller than telescopes on Earth (in fact, it is about a quarter the size of the mirror of the Large Observatory Telescope), but without the effects of atmospheric distortion, it can take images of billions of light galaxies – in a few years. You just have to look in that direction long enough to get the light from it.
Also, some telescopes have a small secondary mirror to correct this atmospheric turbulence, but this is not common. That is, the process is as I told you, but the distortion does not occur in the main mirror, but in a small mirror, which is part of the device we use to see.
Stars change intensity
You may have heard that stars twinkle because they emit different amounts of light. Admittedly, the change is not so noticeable as to cause the night sky to flicker, and it occurs over a longer period than a few seconds. In fact, some stars are known to vary in brightness and size, and we use them to better study the universe. In short: Stars twinkle because a planet’s atmosphere distorts its light before it reaches us.
Because they are so far away, we can only see tiny specks of light, so this distortion occurs, and the closer you get to the horizon, the more pronounced this distortion will be. In the case of the planets, although they appear larger to the naked eye, they appear to us as small discs of light, and enough light penetrates the atmosphere so that the distortion of light from the atmosphere is not noticeable.
Why stars shine: the atmosphere
The light that leaves the star and travels far to Earth barely bends. Drive in a straight line. When it has to pass through the atmosphere, its trajectory changes. Although the atmosphere is transparent, it is not a layer of uniform density. Compared to the upper layers, there are denser parts. In addition, warm air rises during the day, which is less dense than cold air. All this causes turbulent gas in the atmosphere. We insist, but transparently.
When starlight reaches us, it must pass through the atmosphere. It deflects slightly each time it encounters air layers of different densities. It breaks when moving from one density medium to another. And so on, continuously. Since the air is in constant motion, we think that the little dance of the stars is also constant and gives the impression that they are twinkling. These small deviations can also cause them to change color, just like the sun does when it sets over the horizon.