Distant view
A clear, far-reaching view into the distance , which usually also allows an overview of the structure of the landscape , is referred to as a distance view or good distance view .
Conditions for good visibility
Good visibility has several requirements of a geographical, meteorological and physiological nature:
- A suitable location , for example on a tall building (town or church tower , observation tower ), on a mountain top or on a prominent step in the terrain , such as the mountain station of a cable car. The view from a commercial aircraft offers a particularly wide view (distance view at approx. 12,000 m altitude up to 300 km).
- The broadest possible viewing angle ("free horizon "), which is ideally between 180 ° and 360 °, but must be at least 20 ° for a visual impression of the room (for example on a path between trees or rocks).
- Good meteorological visibility conditions with little water vapor , dust or haze in the earth's atmosphere .
- Good and relaxed eyes, whose well-being can be contributed to by blinking several times. Exerted staring into the distance does the opposite.
Maximum values of visibility
- for calculation see article Visibility -
On earth, good visibility is usually around 50 to 100 km away, but close to a large city 30 km can appear extraordinary. The greatest possible visibility in the high mountains and favorable climatic zones (e.g. western Cordilleras ) or weather conditions (e.g. foehn ) is around 150 to 300 km. The fewer aerosols the air contains, the better its transparency . B. in aviation - there are special definitions and measuring instruments .
Good visibility is also advantageous for nautical and geodesy purposes. With coastal or visual navigation one reckons with a few km to 20 km, in which area u. a. the visibility of the beacon is. Due to the mostly moist oceanic air, the visibility is less than on the continent. With a telescope , on the other hand, the view is hardly better than with open eyes because the contrast decreases. Nevertheless, sight lengths of 30 to 60 km are possible for large-scale geodetic angle and distance measurements . Good weather conditions or the lighting of the target points are necessary for this. B. Gauss invented the heliotrope to reflect the sun.
In the mountains and on the edge of industrial areas , there is often the best visibility just after heavy rain , when the air z. B. is particularly dust-free and dry for a short time when the weather is on the rear Really clear air is usually only given when the peplopause is exceeded , an approximately 2 km high boundary layer under which there is little mixing. On the other hand, the best viewing conditions on the earth's surface are from a low orbit .
Distant view from space
As early as 1960, the first photos from the beginning of space travel showed that the steep (especially vertical ) view through the earth's atmosphere is clearer than originally expected (see literature below). Again and again, even experienced astronauts report their surprise at the fine details they can see from the spaceships . According to some space medics , the change in optokinetic nystagmus (unconscious eye tremors) in weightlessness also contributes to this.
The greatest possible distance is a view of the starry night sky . Occasionally falling stars are about 100 km away, aurora borealis a few 1000 km, the planets with many millions of kilometers 10 to 100,000 times further away, and the next fixed stars with 4½ - 10 light years again at a million times further distance. The most distant, freely visible object is the Andromeda Nebula (astronomically the galaxy M31 ) at a distance of about 2.5 million light years.
See also
literature
- Bernhard Edmaier , Angelika Jung-Hüttl: Earthsong . 2nd Edition. Phaidon, Berlin 2005, ISBN 978-0-7148-9424-9 .
- Johann Bodechtel, Hans-Günter Gierloff-Emden : Space pictures, the third discovery of the earth. List, Munich 1985, ISBN 3-471-77625-7 .
- Herbert Schober: Seeing. Volume 1. Fachbuchverlag, Leipzig 1957 ( DNB 454441312 ).
- Gottfried Gerstbach : Eye and sight - the long way to digital recognition . In: Star Messenger. Issue 2000/8, pp. 160–180, Vienna 2000.
- NASA , Office of Technology Utilization: Exploring Space with a Camera. Washington DC 1968.
- Albert Ducrocq : Man in Space . Volume 175/176, Rowohlt's German Encyclopedia, Reinbek near Hamburg 1963.