Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.

Astronomical Catalogs

There are a LOT of catalogs with information on celestial objects, each of which gives its objects a different designation. It can be confusing to try to remember a random combination of characters, so let me try to provide a little background and description for the main catalogs. I'll concentrate on stellar catalogs, but include a few others which appear frequently.

alpha Orionis
Bright stars are named with a lower-case Greek letter and the genitive case of their constellation's name. These designations date back to 1603, when Johann Bayer published a star atlas named Uranometria. The letters are assigned approximately in order of apparent brightness (brightest = α, second-brightest = β, etc.), but occasionally fall out of order. The Greek alphabet has only 24 lower-case letters, so if a constellation had more than 24 stars in Bayer's catalog, he continued with the upper-case Latin "A", and then lower-case Latin letters "b", "c", etc., but omitting "j" and "v". For example, an ellipsoidal variable star in Perseus, HR 1324, is known as "b Persei."

61 Cygni
English astronomer John Flamsteed created an atlas, Historia Coelestis Britannica, in which the stars within each constellation were given numbers. The numbers run by the position of each star (its Right Ascension), not brightness. These designations tend to be used for stars which are somewhat fainter than those with Greek letters, but still visible to the naked eye.

M 74
French astronomer Charles Messier hunted comets with a passion. In his sweeps across the sky, he came across many non-stellar objects which could be confused with comets. He made a list of the prominent ones so that he wouldn't confuse them with real comets. His list includes a bit more than 100 objects, a mix of galaxies, nebulae and stellar clusters.

NGC 2028, IC 328
The New General Catalogue is a compilation of many different catalogs of non-stellar objects; most of them come from the work of William Herschel and his son John. The NGC was put together by J. L. E. Dreyer and published in 1887. Its entries are sorted by Right Ascension. The Index Catalogues were supplements to the NGC, published roughly ten and twenty years later.

BD+17 4708
The Bonner Durschmusterung was a breakthrough, increasing the number of stars with well-measured properties by at least a factor of ten. Over the period 1852 to 1859, Friedrich Argelander, director of the Bonn Observatory, and his assistants Thormann, Eduard Schonfeld, and A. Kruger, made nearly a million individual observations. Their final catalog, often abbreviated BD, contains positions and magnitude estimates for 324,198 stars (each of which was observed at least twice). It's an amazing feat, especially since Thormann left the group in 1853. The catalog extends down to roughly ninth magnitude.

HD 209458
The Henry Draper Catalogue, published in a series of volumes of the Annals of the Astronomical Observatory at Harvard College over the years 1918 to 1936, was another huge leap forward. It included positions, photographic and photovisual magnitude measurements, and spectral types for over 270,000 stars. It was the first big catalogue which included spectral classification, which indicates both the temperature and size of a star.

SAO 22045
In the 1950s, astronomers at Palomar Observatory used the 48-inch Schmidt camera to photograph the entire northern sky in two passbands, using blue-sensitive ("O") and red-sensitive ("E") photographic emulsions. Another big Schmidt camera in the southern hemisphere took pictures of the southern skies. The Smithsonian Astrophysical Observatory measured stars on these photographic plates and created the SAO Catalog, which contains positions, proper motions (based on changes in position since previous surveys), magnitudes, spectral types, and cross-identifications to many other catalogs.

GSC 00019-00485
As the Hubble Space Telescope was being designed and built in the 1970s and 1980s, astronomers realized that they would need very accurate positions for very many stars in order to point HST accurately at its targets. They scanned the big sky survey photographic plates, digitized the results, and wrote computer programs to find and measure stars in the digitized images. It was a big task, but they finished it in time for the scheduled launch of HST. The resulting Guide Star Catalog went much fainter than previous all-sky catalogs, down to roughly fifteenth magnitude (though it was not complete -- it didn't try to include ALL fifteenth magnitude stars). The GSC was distributed widely and used in many planetarium programs as the main stellar catalog. Beware the GSC magnitudes: they are approximately V-band, and only accurate to about 0.5 magnitudes. There have been several versions of the GSC, each one containing more accurate reductions.

USNO-A2.0 0900-07162973
Astronomers at the US Naval Observatory needed very accurate positions for stars all over the sky, fainter than those included in the GSC. The re-scanned the big photographic surveys and measured stars almost down the limits of the plates, about nineteenth magnitude. The USNO A2.0 Stellar Catalog contains positions and magnitudes in two passbands, blue ("B") and red ("R"), for over 500,000,000 stars.

USNO-B1.0 1077-0629947
This is another creation of the US Naval Observatory. It is even better than the USNO A2.0, containing measurements of stars from five sets of plates (two blue-sensitive, two red-sensitive, one near-IR) over a period of several decades. It includes proper motions and magnitudes.

HIP 113397, TYC 1717 2193 1
In 1989, the Hipparcos satellite was launched on a mission to measure very precise positions for tens of thousands of the brightest stars in the sky. Using these precise positions measured many times over the three-year lifetime of the mission, scientists were able to calculate the distances to thousands of stars with much higher precision than ever before possible in bulk. The Hipparcos catalog contains high-precision positions, proper motions, parallaxes (from which distances can be derived), magnitudes, and more for about 120,000 stars, down to about seventh or eighth magnitude. The Tycho catalog contains data with lower precision for many more (over 1,000,000) stars, down to about ninth or tenth magnitude.

SDSS J151605.40-000357.8
Since 1998, the Sloan Digital Sky Survey has been scanning portions of the northern sky from its perch high in the San Francisco Mountains of New Mexico. It has taken images of a large portion of the sky in five optical passbands, and also acquired roughly one million spectra of galaxies, stars and quasars.

In order to make an efficient search through any of the catalogs stored at SIMBAD, you can use the Vizier catalog search tool. This tool will let you select objects from any catalog according to your choice of criteria. For example, let's do a search together: let's find all the stars in the Bright Star Catalog which are brighter than magnitude V = 0.0.


    Simple searches:

  1. What sort of object is NGC 7741? Write down its RA and Dec, please.
  2. What sort of object is 3C 144? Bonus points for explaining what "3C" stands for ....
  3. What color are the brightest stars in M3?

    Catalog queries:

  4. How many bright stars -- where "bright" means "B magnitude less than 10.0" -- are there within a circle of radius one degree centered on NGC 7741? Query the SIMBAD interface to the USNO A2.0 catalog
  5. How many faint stars -- where "faint" means magnitudes between 16 and 22 -- are there per square degree around the variable star R Virginis? (Hint: pick a small region, maybe a circle 3 arcminutes in radius, count the stars, then compute the number per square degree assuming a constant density.)
  6. Use the SIMBAD interface to the Hipparcos Catalogs to run a query on the Hipparcos Main Catalog, I/239/hip_main.

For more information

In addition to the special catalog searches mentioned above, you can always try the good old boys:

I love reading about the history of astronomy. One of my favorite books is J. B. Hearnshaw's The Measurement of Starlight, which focuses on the instruments developed in the past two centuries to measure stellar brightness. You can find a copy in the RIT Library.

Creative Commons License Copyright © Michael Richmond. This work is licensed under a Creative Commons License.