Flicker of stars

To distinguish with a simple eye a fixed star from a "wandering" planet, that is, very easily, even without knowing the sky map. The planets shine with a calm light, flicker of stars and constantly shimmers with different flowers. Especially strong and colorful the flicker of stars can be seen in frosty nights and windy weather, and after the rain, when the sky quickly cleared of the clouds. The stars above the horizon flicker more noticeably than those burning high in the sky; the white stars are stronger than the yellowish and reddish ones.

The planets shine with a calm light, flicker of stars

Like radiance, the flickering of stars is not a property inherent in the stars themselves; it is given to them by the earth's atmosphere through which the rays of the stars must pass before the eye of man is reached. Rising above the troubled gas shell, through which we consider Universe, we would not notice the flicker of the stars: they shine there with a calm, constant light.

The cause that causes the stars to flicker is the same that makes distant objects tremble when in hot days the soil is strongly heated by the Sun.

Starlight has to pierce then not a homogeneous medium, but gas layers of different temperatures, different densities, and hence, of different refractivities. In this atmosphere, as if scattered numerous optical prisms, convex and concave lenses, constantly changing their location. Rays of light undergo numerous deviations from them direct way, then concentrating, then dissipating. Hence - frequent changes in the brightness of the star - the flicker of stars. And since refraction is accompanied by color scattering, along with variations in brightness, color changes also occur.

It remains to explain why the flicker of stars exists, but the planets, unlike the stars, do not flicker, but shine smoothly and calmly. The planets are much closer to us than the stars; they therefore appear to the eye not as a point, but as a luminous circle, a disk, although so small in angular dimensions that, owing to their blinding brightness, these angular dimensions are almost imperceptible. Each individual point of such a circle flickers, but changes in brightness and color of individual points are made independently of each other, at different instants of time, and therefore replenish each other; the dimming of the brightness of one point coincides with the intensification of the brightness of the other, so that the total strength of the light of the planet remains unchanged. Hence - the serene, flickering glare of the planets.

Hence, the planets seem to us flicker because they flicker at once in many points, but at different times.