Earth's shadow
As Erdschattenbogen, imprecise shortening also called Earth and it refers to the after sunset and before sunrise in cloudless weather conditions over the horizon visible projection of the earth's shadow in the opposite twilight sky. He always is at its highest against the sun's position as he approaches the horizon to the north and south.
Near the horizon haze layers are indeed often seen before the sunset, but can easily be confused depending on appearance after sunset with the Erdschattenbogen.
- 2.1 documents
- 2.2 External links
- 2.3 See also
Formation
When the sun is below the horizon - more precisely, during the civil twilight - achieved the direct solar radiation is no longer the lowest layers of the atmosphere. This will of them significantly less light reflected back as from the still -lit upper atmosphere. This dark, gray-blue bottom layer is the Erdschattenbogen, the purple- orange light phenomenon over the counter dusk.
Influence of atmospheric ozone
The French meteorologist Jean Dubois found out in 1951 that the blue -gray color of the shadow is caused by the ozone molecule. As the American geophysicist Edward Hulburt 1952 described in more detail, the ozone molecule is excited at the absorption of sunlight to stretching vibrations, leading to broad and diffuse absorption bands (called Chappuis absorption bands ). In the range of visible light, these bands are particularly pronounced at 600 nm, thus ozone absorbs predominantly orange light.
In the daytime, this absorption is hardly noticed by ozone, it is outshone by the blue of Rayleigh scattering. As in the twilight is longer for an observer by the shallower incidence of the way the sun's rays in the atmosphere due to Rayleigh scattering in the west the longer wavelength yellow and red radiation left over, which is typical for sunsets. The influence of ozone on the sky color contrast increases with decreasing solar elevation, the longer path of the light through the ozone layer allows the effect of the Chappuis absorption increase significantly. Up to 40 percent of the orange light is filtered out, which is enough to leave a visible trace in the sky. The selective absorption shifts the residual light toward the blue end of the spectrum.