Transit telescope

An instrument passages (also: passage, transit instrument or lunch tube) is a measuring instrument of Geodesy and Astrometry Astro, which defines with its horizontal axis arbitrary vertical circles. It is used to watch on a vertical reticle the times of star passages and is a result of its installation - Portable design in a limited way - over the meridian circle very compact. In contrast to the meridian circle is not used to measure Sternörtern but to astronomical lengths and timing, and partly to the azimuth measurement.

The principle of the instrument in 1689 by the Dane Ole Rømer ( Olaf Roemer ) was invented and used for the determination of time by observing the meridian passages of stars. These mounted Roemer a about a fixed, exactly horizontal east-west axis ( tilt axis ) rotatable telescope and registered the star passes through the beats of a precision pendulum clock. Since the end of the 19th century, the construction has prevailed as a broken telescope.

Operation

All astronomical objects through the celestial meridian horizontal. With an aligned according to the meridian telescope and a registered chronometer can determine the right ascension of a star exactly. From its apparent height during the passage of the declination can be determined if the pile height is known ( astronomical width) and a vertical circle is present.

The star passages are measured by a parallel " reticle " (previously there were actually strands of specific species of spiders ) or, for better accuracy, with an optical micrometer and electrical contacts ( " impersonal micrometer ", see also: Universal Instrument). The time registration was until about 1980 with tape or pressure chronographs, with today's digital applications.

The measured times or angles must (as with any precision measurement) to the influence of small Achsneigungen corrected ( be "reduced", which is done with 2-3 dragonflies and the " Mayer- formula " ( by Tobias Mayer).

The measurement accuracy to be higher at about 0.1 ", but with averaging a number of star passages. Even the first, in 1700, designed by Ole Römer device achieved approximately 1 ". The time measurement is visually accurate to about 0.02 seconds, and with micrometer even better. In both cases, the "personal equation " (reaction time) must take into account, however. It amounts to an average of one tenth of a second (depending on the observer 0.05-0.2 s ), but is a few hundredths of a second constant. For the determination of possible small changes in the reaction time was the "artificial star" developed.

Applications

The passages instrument is a smaller form of the meridian circle, with which one can measure the transit times of stars across the meridian, and with additional devices, the zenith distance. In the first place (s) it serves to determine

For a tripod, the instrument is too heavy, even though it in size a precision theodolite not significantly outperforms. Therefore, it requires a measurement pillars, as they are built on fundamentals such as points or stakeout long tunnel.

Because of their compact design, passages instruments were used not only to observatories, but until about 1980 isolated on field stations. Some of these instruments had a slightly different version of height or dragonflies circle and could be used to some extent outside the meridian ( azimuth and zenith distance measurements and the deflection of the vertical ).

A well-known manufacturer of the instruments was the company Askania in Berlin and until about 1920 more companies like Starke & Kammerer (Vienna ), Johann Georg Repsold (Hamburg) or English workshops.

Also, radio telescopes are sometimes built as transit instrument, as they must be designed to be movable in only one axis. Radio sources, however, can be observed only once a day. An example of this is the built- in one basin Arecibo Observatory in Puerto Rico.