Vertical direction

The plumb line, even the solder or vertical, is the local direction of the acceleration of gravity, so it shows "down". It is perpendicular to the equipotential surfaces of the Earth's gravity field in the direction of the resultant of the gravity of the earth and the centrifugal force due to the Earth's rotation. Due to the perpendicular direction to the Earth flattening deviates to 0.2 ° from the direction in which the center of the earth is decreases. The upper intersection of the perpendicular direction to the celestial sphere is called the zenith, the lower nadir.

An easy way to determine the local plumb line, the plumb bob.

The horizontal, and the horizontal or the mathematical horizon, is a name for a plane perpendicular to the plumb line.

Physical definition

Physically considered is the plumb line in the gravitational field of the rotating earth a consequence of the gravitational and (to a lesser extent ) the centrifugal force. Therefore, they are usually not facing the center of the earth. The rotation ( and the resulting centrifugal force and flattening ) causes a deflection which is at the earth to 0.2 °, and Saturn almost 10 °. To this amount the geocentric latitude is smaller than the geographical.

More specifically, the plumb line is not a straight line but a curve in space. It pierces the plumb line as all level surfaces of the gravity field orthogonal. The Lotkrümmung can be determined by complex measurements (see gravitational gradiometry or ) or computationally by modeling the masses of the site ( topography ) and the geological subsurface. The curvature is in the lowlands about 1 " in the high mountains but over 10 ", what to centimeter decimeter per kilometer mind some.

Astronomical and geographical coordinates

From the perpendicular direction or the position of the zenith in the night sky to accurate values ​​for the astronomical latitude and longitude can be determined. The difference with the latitude and longitude of the so-called vertical deflection caused by the irregularities of the Earth's gravity field. They form an important coordinate system for the earth sciences - especially geodesy.

In contrast, form the horizon and plumb a topozentrisches horizontal coordinate system that has the greatest significance for everyday life and is also called the natural coordinate system.

Measurement and accuracy

The measurement of the perpendicular direction is performed:

• In construction with plumb bob ( plummet ) or staff level, and 90 ° to the water balance and leveling - accurate to approximately 0.1 ° to 0,001 °;
• In surveying with theodolite and special devices such as the astrolabe or Zenit camera - Accuracy 1 " to 0.1 " (in conjunction with Lotsensoren like dragonflies or compensators)
• In physics with a variety of instruments and accuracy;
• In geodynamics as Lotrichtungsschwankung with special instruments in disused tunnels or underground mines ( vertical and horizontal pendulum) to ± 0.01 " and more accurate.

Etymology

" Plumb " is derived from the plumb line from, "Vertical " from the sinker, " Horizontal " probably of " balance " as a synonym for an equilibrium water surface - see spirit level as the original instrument for this purpose. " Horizontal " refers to the plane of the horizon and has to do with sweeping views. In medicine, refers to that vertical line drawn from the vertex to the sole. " Vertical " derives from the Latin ( Vertex " vertex ( point )"; same meaning is the "diagonal " basis ).