Brightness catalog

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In astronomy, special star catalogs are referred to as brightness catalogs , in which - in contrast to the position catalogs - the apparent brightnesses of the stars they contain are the main content. The positions ( star locations ) are only required to identify the stars.

The brightnesses are measured using the methods of photometry . Today a distinction is made between photographic , photo-visual and photo-electric methods, while until the late 19th century, measurements were predominantly carried out visually . From the middle of the 19th century, a wide variety of types of photometers were developed, which replaced the standard Argelander estimation (after Friedrich Wilhelm August Argelander ). With all methods, including today's methods, brightness differences are measured, which can be brought into a uniform system using known standard stars.

The most important photometric catalogs are therefore those of precisely measured standard stars. Numerous observatories worked on the creation of such catalogs between around 1870 and 1900, including the observatories of Göttingen, Hamburg, Leipzig, Vienna and Lemberg in Central Europe, and above all the Yerkes and Harvard Observatory in the USA . This resulted in extensive catalogs such as the Göttingen actinometry and the Yerkes and Harvard photovisual photometry , each with around 3,000 stars. For the purpose of calibration , a selection of particularly precisely photometriced stars around the northern celestial pole around 1900 for the north polar sequence ( NPS) or the Harvard pole sequence (HP) was extracted, from which the International Pole Sequence (IPS) emerged in 1922 . In the course of time, all other - over 100 - brightness catalogs were reduced on their system .

The totality of these data collections compiled by observatories today comprises over 500,000 stars, to which there are also those somewhat less precise the astrometric satellites HIPPARCOS (1990–93) and GAIA (from 2015). The IPS used for calibration until the 1960s has now been supplemented by even more precise calibration fields distributed over the whole sky .

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