Mural instrument

A mural quadrant is a historical astronomical instrument, with the exact amount of angles and positions of stars were measured. He was until about 1800 in use and is the predecessor of the Meridian Circle.

Design

The basic construction is the same as in the classic quadrant. It consists of

  • A quarter circle (but with a larger radius ), with a precise circular pitch
  • The associated readout device,
  • A target device (up to about 1650 a visor, then usually a long scope) as well as
  • A plumb bob, later a dragonfly, as an artificial horizon.

In contrast to the smaller quadrants, which were held in the hand or placed on a tripod, the mural quadrant is running permanently on a north -south, exactly vertical wall mounted. This can be reliably detected planets in their culmination and their transit time can be measured accurately. The stable formation greatly enlarging measuring telescopes, the measurement accuracy has been significantly increased.

Tychonischer mural quadrant

Until the invention of the telescope of the mural quadrant of Tycho Brahe was the most accurate of its kind He stood Danish Tycho's observatory Uranienborg and had a quarter of a circle of two meters radius to 10 "( 0.1 mm) was supposedly doing to read. The instrument of Copernicus ( 1520 ) should not indeed have been much smaller, but mounted on a wood panel, and the circle was divided into 0.5 °, which allowed angle estimates of about 0.05 °.

The freiäugige sighting of the stars could Tycho as an experienced observer to carry on about 1 ' ( one minute of arc ), which corresponds to the optical selectivity of the eye. He scored so that 2 - to 5 -fold more accurate measurements than before, which was a key requirement for Johannes Kepler's planetary theory. Kepler himself, his assistant and successor, hardly made ​​measurements because he had an eye defect.

Main instrument Observatories of 17-18. century

With the growing importance of celestial mechanics and improved star catalogs demands increased accuracy. When they therefore end of the 17th century passed on measuring scopes with higher magnification, were large, aligned due south wall quadrant as the main instrument of many observatories. The reference to the mathematical horizon set forth seconds dragonflies, on some devices even ocular micrometer were attached (invented by Ole Römer 1680 ), which enabled the visual field of the telescope fine measurements.

With these developments have been achieved by 1700 measurement accuracies of 1-2 ". Fix mounted quadrant allowed now in addition to the determination of time (to about ± 0.1 " ) and the measurement more accurate star positions and the latitude. At the observatory Specola of Bologna was reached in 1710 even 0.8 ". James Bradley discovered with such an instrument in 1725, the annual aberration of the " fixed stars ", which the heliocentric world view has been detected for the first time.

Later Meridian Instruments

The mural quadrant was replaced in the 18th century by the meridian circle, in which the telescope throughout the Meridian can spread from the southern point on the zenith to the northern point. Also astronomical and geodetic instruments have been developed that higher accuracies achieved with smaller dimensions, because a compact design is less sensitive to instrumental errors and temperature influences. In addition to the transit instrument and the instrument passage even more flexible universal instruments were increasingly used, with whom in 1920 0.1 " were already reached. Today, the astrometry of planetary and star positions is carried out with automatic meridian circles and with so-called astrometry.

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