Sky

As the sky, more generally, the surface of a planet seen from the Earth or through the atmosphere with a view towards space panorama is commonly referred to.

The heavens

As the heavens are referred to the portion of sky ( firmament ), the arches as the apparent hemisphere above the horizon.

In fact, the arch of heaven as a flat dish that is two to three times farther on the horizon than at the zenith appears to us rather. This is due in large part to the different Azur (sky blue ), next to also wear effects of distance estimation with respect to the visible horizon at as they are the moon illusion is based. The appearance of the sky as the earth curved shell is present in many mythologies and has contributed to the long existence of a geocentric.

The daytime sky

Why is the sky bright?

Penetrates the sunlight, the atmosphere, some of the light is scattered and brightens as the sky. Without this atmosphere without scattering and the sky as space would be "black". To this diffuse radiation contributes significantly to the spread air particles in the atmosphere. Another, especially visible at dusk cause is the absorption behavior of the ozone layer.

The sky blue

During the day the sky gets its blue color due to the scattering of sunlight by the molecules of the Earth's atmosphere. The blue short-wavelength end of the spectrum is about 16 times more scattered than the red light. Depending on the angle to the sun, the scattered light varies strongly polarized.

The solar radiation that normally appears to us as white color perception is based on the spectrum of visible light. Since all spectral colors in the solar spectrum are present, it appears as bright and white. , The white light is scattered, for example using a prism, the different spectral colors are spatially separated perceptible. Color effect is produced when some of the spectral components of the sunlight is stronger or weaker than the available white light.

When the day sky blue, the sunlight is scattered by minute air molecules that are much smaller than the wavelength of light ( Rayleigh scattering ) and can then pass from any direction in our eyes. The picture shows that the maximum intensity of the direct solar radiation in the green spectral range, but far wanders the maximum of the scattered light in the UV range. The invisible UV light enough for sunbathing. The sky seems to shine and this preferably with short-wavelength light, which perceives the human being as blue.

The place with the bluest and clearest skies of Earth, so the most intense day sky blue, according to measurements of the British National Physical Laboratory Rio de Janeiro. There is in the upper layers of the atmosphere very little condensed liquid (water droplets ) and dust particles that could interfere with the passage of the short-wavelength blue light, which makes this particularly brilliant blue results. Unfavorable scattering effects in the atmosphere, about to haze or smog, let the sky elsewhere appear more whitish- blue.

The blue sky at sunrise and sunset and particularly the intense blue of the sky during twilight and clear sky has a different physical origin than that of Rayleigh scattering. The, also known as Blue hour ozone days time is based on the specific absorption behavior of the ozone layer at 20 to 30 km altitude and was only in 1952 by the American geophysicist Edward Hulburt ( 1890-1982 ) discovered.

Historical

Leonhard Euler drew on July 27, 1760 by light to natural oscillations excited particles approach to explain the blue of the sky. In the 19th century Tyndall showed that light is scattered by colloids ( small droplets, dust) ( Tyndall effect ), and Strutt (Baron Rayleigh ), that light is scattered more strongly to colloids, the shorter the wavelength, it is ( Rayleigh scattering). However, light scattering on colloids could explain the color of the sky not quite, as little as a function of the amount consists of colloids in the atmosphere. Therefore, it was thought by other scientists that the much smaller molecules of nitrogen and oxygen for the light scattering would be responsible. For scattering at such small particles but there was no explanation model. It was not until Einstein described a model for photoelectric effects on molecules, which was consistent with many experiments.

However, an inconsistency remained: the deep blue of the sky during twilight. According to the theory of Rayleigh scattering of short-wave blue portion of sunlight even during the passage of the sun rays through the long path in the atmosphere should be sprinkled (with depression about 35 times longer than high sun ) during a sunset out and the sky would actually in Zenit appear gray to black.

This phenomenon was first discovered in 1952 by the American geophysicist Edward Hulburt and could be also explained by him. Hulburt was able to prove that the sky blue at the zenith during the sunset is based on only one-third of the Rayleigh scattering, but two thirds based on the specific absorption behavior of the ozone. At dawn, however, the blue light of the sky is completely caused by the ozone layer.

The sky at other times

Similar relationships also apply to the night sky, but they are barely visible to the naked eye. For a number of other effects are apparent that the articles night sky in more detail. With the sight of the stars of the articles dealt starry sky, with the atmospheric phenomena of the day - and -night change of Article dusk.

Looking at the sky from the outside

Although the blue component of sunlight is scattered in the atmosphere in all directions, ie also in the back space, the " blue sky " is barely visible from space. The intensity of the scattered light of the atmosphere is too low in relation to the reflected light from the surface. From space considered is why you see only the much brighter background of the sky: the earth's surface. From the surface of the sky against the dark background of space is considered. The night side of the earth is due to scattering effects never completely dark, in particular - apart from the cloud cover - by manmade light pollution.