Sun counterpoint

The opposite point of the sun is an imaginary point on the celestial sphere , which lies in exactly the opposite direction to the sun . It corresponds to the point that results from an extension of the Sun- Observer ray .

As long as the sun is above the horizon , the sun's counterpoint is therefore below the horizon. If the sun is at the zenith , the sun point is in the vertical direction at the feet of the observer, i.e. approximately in the direction of the center of the earth . At sunrise and sunset the opposite point of the sun is in the horizon (in the 180 ° opposite direction).

Sometimes it is easy to see in a plane (see picture) or in deep sun on an isolated mountain peak . However, the photographic contrast is low.

This point is especially important in atmospheric optics , i.e. for all phenomena that are based on sunlight . For example, the opposite point of the sun forms the imaginary center of every rainbow . The counter- twilight rays also emanate from it and sometimes the counter-glow can be observed there.

visibility

The counterpoint of the sun near the horizon, taken from a commercial airplane

An observer who has the sun exactly behind his head can find the opposite point of the sun by fixing the center in the shadow cast by his own head (see also Brocken Ghost ). In the case of projection surfaces that are damp due to dew, a whitish halo can even appear as a natural phenomenon.

If the screen is so far away that the apparent diameter of the sun is greater there than the apparent diameter of the object, which would cause a shadow at closer projection, will become apparent to the observer in circumstances penumbra -, scattering or diffraction patterns in antisolar point like for example with the Glorie .

In addition, a counter-twilight can sometimes be visible at the sun's counterpoint .