Anti twilight arch

What is an anti twilight arch?

The colors of the sunset when the sun is low on the horizon are due to light rays that pass through a thicker atmosphere to the horizon and vertically.
The largest fog late at night is causing small differences between the 2 twilight (morning and evening).
The sky is pink and orange in the morning and evening colors are more pastel and pink in the East and West. On the other side of the sun, one can notice an amazing phenomenon is the arch anti twilight.
The anti twilight arch or anticrepuscular rays or the belt of Venus is the projection of the Earth's shadow on the lower layers of the atmosphere.
This phenomenon is visible to the naked eye, is seen at dusk in the east in the evening shortly after sunset in the west where the morning shortly before sunrise.

This strip of blue gray, alights on the horizon as the sun rises slowly in the opposite direction.
The evening As the sun sinks below the opposite horizon, it rises slowly, parallel to the horizon.
While the region of sky surrounding the sun form a task very bright, straw yellow color that will gradually turn orange, the color opposite the ballet begins a few minutes after the disappearance of the sun.
When the sun goes down, the orange zone that surrounds form a semicircle and east, the Earth's shadow begins to appear above the horizon.
It is during sunset with a slightly cloudy sky as the colors are beautiful.

Image: In this photo of Bay Bénodet (finistère - France), is projected into the atmosphere, the Earth's shadow.
This arch anti twilight, as the name suggests, is observable in the direction opposite to the sun.
This phenomenon scatters light in shades of red, pink, purple and blue on the horizon. Also called the anticrepuscular rays, Belt of Venus.

Observation of the anti twilight arch

One can watch the sunrise from the blue shadow of the Earth a quarter of an hour after sunset.
This gray-blue band rises slowly above the horizon. What we observe is the projection of the shadow of our globe on the lower layers of the atmosphere.
A few minutes after sunset, the shadow of the Earth to separate penalty rises and shows a wider area a little pinkish, that the ark itself.
While the rising shadow of the Earth is becoming more diffuse, the blue sky begins to become gloomy, it is called cons-dusk.
The curved arch and shows the roundness of the Earth. At the latitude of 45 °, the duration of the phenomenon, in the heart of winter, is about 25 minutes.
The phenomenon is reversed at sunrise. The poets also call this phenomenon the Belt of Venus.

To observe this natural spectacle, look, while the sky is still shining lights of the last sunset on the other hand, the horizon must be sufficiently clear about the point sunscreen to see the long shadow of Land bordered by a scalloped purple. It is not difficult to observe in plain, it is bent.

Image: Duration of the twilight arch depending on the geographic latitude and months of the year.
The variation of the luminous phenomenon following geographic latitude and next season is given by the Bureau des Longitudes.