Zenith

The zenith of a point on the Earth's surface is prolonged upwards perpendicular direction, the perpendicular to the horizontal plane. It is the point of the sky, which is located just above the observer. The base point is called the nadir.

The name comes from the Arabic سمت / including /, path, road, direction ', or more precisely of سمت الرأس / including ar -ra ʾ s /, the direction of the head, vertex '. By spelling errors and incorrect readings was in medieval texts, including the spelling CEMT or zemt and it cenit or zenith.

On an imaginary spherical earth would be the zenith of the beam, the (perpendicular to the earth's surface ) runs starting from the center of the earth upward. However, since the Earth is not a perfect sphere, a more precise definition is needed. On the reference ellipsoid of geodesy, it is the Ellipsoidnormale. In astronomy, however one defines it as an extension of the local gravity vector. The Misweisungen between terrestrial and astronomical geodesy are well recognized around the world today.

In fact, because the ideal mathematical horizon does not match the visual, the horizon is therefore not directly ermessbar, the zenith, the central position at all: Precision is defined as the vertical plane to the vector of the observer to the zenith in the point of the observer, the horizontal plane. first one determines the zenith, and then the ( idealisiertenen ) horizon. Therefore, together with the celestial poles and the south point it is of central importance for the topocentric horizontal coordinate system ( azimuth and elevation ). Together with the celestial poles defines the zenith the meridian plane. The intersection of the horizon and meridian plane defined South Point and North Point, and with the Vektortripel of observer to the zenith, to the North (or South ) point and according to the East or West Point, the coordinate system is stretched (there is for the azimuth of counting of from the north and south from, or counter -clockwise).

The angular distance of a celestial body to the zenith is the zenith distance and is the complementary angle of the astronomical amount. All the stars that reach the daily run to the highest point of its apparent path in the zenith, have a declination equal to the latitude of the observer.