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.
- The Interactive
NGC Catalog
has pictures and descriptions of some (but not all!) NGC objects;
it also provides quick access to scanned copies of the
Digital Sky Survey at the position of each.
- Since many (most?) of the objects in the NGC and IC are
extragalactic, NED
(the NASA Extragalactic Database) is a good place to look for them.
- 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.
Exercises
Simple searches:
- What sort of object is NGC 7741? Write down its RA and Dec, please.
- What sort of object is 3C 144?
Bonus points for explaining what "3C" stands for ....
- What color are the brightest stars in M3?
Catalog queries:
- 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
- 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.)
- 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.
Copyright © Michael Richmond.
This work is licensed under a Creative Commons License.