Star catalog

Star catalogs are used in astronomy to list a large number of stars according to various properties in book form or to save them in databases . The most important of these parameters are:

the star locations (exact star positions) in the celestial coordinate system ;
the proper motions of these stars, if highly precise star locations exist over a few decades and have been examined for systematic changes;
the spectral classes or the color indices of the stars.

Because of their huge number, most stars are referenced by their respective catalog numbers. There are a number of different star catalogs that have been created over the years for a variety of purposes. This article lists only the most commonly used catalogs. Most of the more recent catalogs can be downloaded from NASA's Astronomical Data Center or elsewhere (see web links ).

Historical catalogs

Ptolemy's star catalog from the 2nd century AD contains stars visible from Alexandria in 1022 . Published as part of his Almagest , it was the standard catalog in the Western and Arab world for over a thousand years. The catalog was based in part on an earlier one by Hipparchus of Nicaea from the 2nd century BC. An even earlier catalog was published by Timocharis of Alexandria around 300 BC. Written and later used by Hipparchus.

Two systems that were introduced in historical catalogs are still in use today: The Bayer names from Johann Bayer's star catalog Uranometria from 1603, in which the brighter stars of each constellation were designated with Greek letters (e.g. γ Orionis or κ Lyrae ) as well as the Flamsteed names from the Historia coelestis Britannica by John Flamsteed from 1712, in which numbers of any size were used instead of less available Greek letters (the same example stars here are 24 Orionis and 1 Lyrae).

Bayer and Flamsteed recorded only a few thousand stars that are visible to the naked eye. A complete listing of all stars is also not feasible for today's star catalogs, since there are billions of stars in the Milky Way alone . For this reason, catalogs are usually limited to a minimum apparent brightness , i.e. work with a defined magnitude limit and omit weaker objects so that the number of objects cannot grow indefinitely.

Catalogs for the whole sky

Henry Draper Catalog (HD / HDE)

The Henry Draper Catalog of the Harvard College Observatory was published in nine volumes between 1918 and 1924 and represents the first large-scale effort to catalog the spectral types of stars. It covers the entire sky and contains 225,300 stars down to an apparent magnitude of 9 ^m . In 1949 the catalog was expanded by 133,783 stars to a total of 359,083 stars. The position data refer both times to the astronomical epoch 1900.0.

The stars in it are referenced with the abbreviation HD followed by the number of the star, e.g. B. HD 185037. HD is also mostly used for the stars in the extension catalog (HDE, HD extension ), as the additional stars are clearly numbered. Today, HD numbers are often used for stars that have no Bayer or Flamsteed designation.

SAO catalog

The Smithsonian Astrophysical Observatory ( SAO catalog ) catalog was created around 1965 for satellite geodesy in the standard epoch 1950.0. It contains 250,000 stars down to 9 ^m from various sources. Hence there is a considerable overlap with the HD catalog. In the northern sky it has an accuracy better than 1 ". A set of almost 200 star maps supplements the 4-volume work.

In the latest edition, the epoch of the position data is J2000.0. The SAO catalog contains additional important information that the HD catalog does not contain, namely the proper motion of the stars. Therefore, it is often used when this is important. In the latest version, the corresponding numbers in the HD and BD catalog are also given.

The names in the SAO catalog begin with the letters SAO followed by a number. The numbers are assigned in eighteen 10 ° bands, with the stars within a band arranged according to right ascension .

Bonn, Southern, Cordoba and Cape Photographic Survey (BD / SD / CD / CPD)

The Bonn survey and its subsequent editions were the most comprehensive catalogs before photography was introduced for this purpose.

The Bonn survey (BD) itself was published by Friedrich Wilhelm Argelander , Adalbert Krüger and Eduard Schönfeld between 1852 and 1859. It contained the locations of 324.198 stars in the epoch 1855.0.

Since it covered almost only the northern sky , it was expanded in 1886 by the Southern Survey (SD) with 120,000 stars and in 1892 by the Cordoba Survey (CD) with another 580,000 stars. Finally, in 1896, the Cape Photographic Survey (CPD) followed with another 450,000 stars.

Astronomers usually prefer the HD designation of a star because it also contains spectroscopic information. However, since the surveys contain significantly more stars, these older names are occasionally used if there is no entry in the HD catalog.

In the survey catalogs, stars are marked with the initials of the respective work (BD, SD, CD, CPD), followed by the declination in degrees and another number. The latter number is more or less arbitrary as there are thousands of stars at each declination angle. Examples of this type of designation are BD + 50 ° 1725 or CD-45 ° 13677.

US Naval Observatory (USNO-B1.0)

The USNO-B1.0 is a catalog of the researchers of the United States Naval Observatory , which contains the locations, proper motions, apparent brightnesses at different wavelengths and estimates for 1,042,618,261 objects for whether it is a star or a galaxy , determined from 3,643 .201,733 individual observations. The data was obtained by cataloging 7435 Schmidt plates obtained from various surveys over the past 50 years.

The USNO-B1.0 is assumed to cover the entire sky down to 21 ^m , an accuracy of 0.2 "with regard to the epoch J2000.0 and an accuracy of 0.3 ^m for the photometric brightness measurement in up to five colors and 85% accuracy in distinguishing stars from non-stellar objects.

Gaia catalogs

The space-based observations of the Gaia mission surpass all previous catalogs in terms of both the number of objects and the accuracy. Gaia records stars as well as galaxies, quasars and objects of the solar system. Due to the observation strategy, Gaia can only detect point light sources, but not large objects such as fog or dark clouds . In addition to the star words, Gaia also provides parallaxes and proper motions, radial velocities and spectra in later publications. Gaia can automatically recognize double and multiple stars as well as variable stars, quasars, galaxies and solar system objects and assign them to a class. The publication takes place in several steps, with different object classes each forming their own sub-catalogs. The limit so far is a G magnitude of G = 20.7, although a number of weaker objects are still included. The last catalogs should be accurate to within a few micro-arcseconds.

Gaia DR1 was released as a preliminary catalog in 2016 and contains approximately 1.1 billion stars and 2,152 quasars (GCRF1). The accuracy is around ∼10 mas for the majority of the objects, with 2,057,050 bright objects of the Tycho-Gaia Astrometric Solution (TGAS) achieving an accuracy of 0.3 mas.

Gaia DR2 appeared in 2018 with 1.7 billion stars with places and magnitudes. The basic accuracy is 0.1 mas for systematic errors, plus a magnitude-dependent uncertainty between 0.02 and 0.04 mas for objects brighter than G = 15 and 0.1 mas for G = 17 and then drops to 2 mas for objects with G = 21. In addition, around 1.3 billion objects have three-band photometry, parallaxes and self-motions. There are radial velocities for more than 7 million bright objects. The sub- catalog GCRF2 contains 556,869 quasars, and 550,737 variable stars are recorded and classified. This is rounded off by a small catalog of around 14,000 known solar system objects. The magnitudes have a magnitude-dependent accuracy between 0.3 for the brighter and 10 mmag for the weakest objects.

The next catalogs should be even more extensive and more precise. Gaia DR3 is announced for the beginning of 2021 and should also contain an object classification according to the spectrum, as well as the spectra themselves. The recorded solar system objects are to be published, as well as catalogs for double and multiple stars. The fourth catalog will contain all the data up to the nominal end of the mission, but a mission extension has been approved and further catalogs are expected after that. The later catalogs should also contain stars with automatically recognized massive exoplanets . All catalogs are accessible to the general public via the Internet.

Further catalogs

Bright Star Catalog (HR)
Positions and Proper Motions (PPM): Catalog of the Astronomisches Rechen-Institut Heidelberg
Tycho and Tycho-2 (TYC, TYC2): 1,058,322 stars up to 11.5 ^m and 2,557,501 to 12 ^m , which were recorded as part of the Hipparcos project (see below ).
Guide Star Catalog (GSC)
USNO CCD Astrograph Catalog (UCAC)

Special catalogs

Specialized catalogs do not aim to list all the stars in the sky, but instead stars or astronomical objects of a certain type, such as. B. variable stars , double stars or very close stars. Special catalogs occasionally do without a magnitude limit, since the number of objects that can be recorded or recorded is limited in some other way.

Aitken Double Star Catalog (ADS)

In his 1932 catalog New general catalog of double stars within 120 deg of the North Pole , Robert Grant Aitken lists 17,180 double stars from −30 ° to 90 ° declination .

Gliese (Gl) and Gliese-Jahreiß (GJ)

The catalog of Wilhelm Gliese (Gl), later with Hartmut Jahreiß (GJ), aims to record all stars within 25 parsecs around the earth. It has been expanded several times:

Catalog of Nearby Stars ( catalog of nearby stars , in 1969, Gliese): the second edition numbered from 1.0 to 965.0. To distinguish it from the stars of the first edition, decimal points have been inserted here. The catalog itself is also referred to as CNS2, but not in connection with the catalog numbers.
Extension of the Gliese catalog ( Extension of the Gliese Catalog , 1970, Woolley, Epps, Penston and Pocock): numbers from 9001 to 9850.
Nearby StarData Published 1969-1978 ( data of nearby stars, published from 1969 to 1978 , 1979, Gliese and Jahreiß): The numbers 1000-1294 are nearby stars called, with 2,001 to 2,159 such, one of which is suspected.
Preliminary Version of the Third Catalog of Nearby Stars ( Preliminary version of the third catalog of nearby stars , in 1991, Gliese and Jahreiß): numbers 3001-4388.

Although the latter version of the catalog has been labeled "tentative", it is still in use (as of September 2001) and is called CNS3. It contains 3803 stars, most of which already had GJ numbers, but also 1388 new ones. An example of a well-known star from this “unofficial” version is GJ 3021 , which is orbited by a planet ( exoplanet ) GJ 3021 b .

→ See also: List of the nearest stars

Hipparcos (HIP)

The Hipparcos catalog was compiled from data from the astrometric satellite Hipparcos of the European Space Agency ESA , which was in use between 1989 and 1993. The catalog was published in 1997 and contains 118,218 stars with unprecedented precision - averaging ± 0.003 ". It is also interesting because of its parallax measurements , which are much more accurate than those made by observatories on the ground. The catalog does not contain measurements of radial velocities .

In addition to these very precise measurements, the satellite also mapped a large number of other stars with somewhat less accuracy. These two Tycho catalogs , Tycho and Tycho 2, contain 1 and 2 million stars, respectively, with an accuracy of 0.03 ".

Fundamental catalogs

In so-called fundamental catalogs , the positions and proper movements of stars are recorded, which have been precisely measured over long periods of time. You define a special, absolute coordinate system, the fundamental system , which largely corresponds to an inertial system.

These "fundamental stars" are used for various types of measurements that require high absolute accuracy, e.g. B. for latitude , plumb line or solar time . The catalog FK3 (1937) was followed in 1963 by the twice as extensive FK4 of the Astronomisches Rechen-Institut Heidelberg with 1535 stars and in 1988 by the fundamental catalog FK5 . The FK6 with 3300 stars , which has been significantly refined with Hipparcos, has been in use since 2000 .