The Mag 5 Star Catalog
by John P. Pratt
Mon 14 Dec 2015 (1 Water)
A new free star catalog in standard spreadsheet format which adds several features to the popular Yale Bright Star Catalog.
For a century the standard catalog of visible stars, down to magnitude 7 (visible only in binoculars), has been the Yale Bright Star Catalog. It is available on line in digital format which can be used either with a special program or can with some difficulty be imported into a spreadsheet (see Bright Star Catalog, version 5.).
For some time in my work there has been a need for a shorter version of the Bright Star Catalog. It is sometimes desirable to sort the catalog by magnitude, by constellation, by spectral class or other criteria. The full catalog is too large to do that on many small computers. There is much that can be deleted from it for many purposes. For example it has both 1950 and 2000 year coordinates. (Star map makers traditionally make maps attached to the earth rather than the stars so they have to be updated every 50 years!) It also has many cross-reference lists to other star catalogs.
The Cambridge Star Atlas
Thus, the first step in the process used to create a light-weight version was to eliminate several columns. In the case of the stellar spectral classification column, much of the detail of emission line elements was eliminated. That version is called the Brief Bright Star Catalog in my work and can be downloaded here. It still contains all 9,110 entries, but just with about half as much information about them. Anyone wanting to restore any particular columns can easily do so from the full catalog, which can be downloaded in spreadsheet format here.
The next step was to delete stars too dim for most people to see, unless they form part of a star constellation figure. One of the desired features of this new catalog is to tie it more to constellations which are the easy way to find your way around the sky without having to resort to complicated coordinate settings on the telescope, usually requiring a computer to use. There is much to said for being able to find stars with binoculars or just the naked eye.
The criteria for deleting stars from the Brief Bright Star Catalog were the following:
All stars with listed Bayer or Flamsteed designations are retained.
All stars in Ptolemy's star catalog are retained (see "Ptolemy's Star Catalog").
All stars with visual magnitudes of 5.50 or brighter are retained.
All others are deleted.
Hence it is called the Mag 5 Star Catalog because it contains all stars that are of fifth magnitude or brighter (rounding down). That resulted in a list of 3,922 stars, making it much more manageable than the 9,110 entries in the Bright Star Catalog.
|A||Bright Star (HR) Number|
|F||Double Star Component|
|I||2000 R.A. (hours)|
|J||2000 R.A. (minutes)|
|K||2000 R.A. (seconds)|
|L||Declination (North or South)|
|Q||B-V Color Index|
|R||U-B Color Index|
|T||Proper Motion (R.A.)|
|U||Proper Motion (Dec.)|
|V||Distance (light years)|
|W||Radial Velocity (km/sec)|
Then several new features were added to the Mag 5 catalog:
It comes in a universal spreadsheet format: .csv (comma separated variables). This is really just a text format where the columns are separated by commas. Because it is significantly smaller than the Bright Star Catalog, it can easily be sorted on any desired sets of criteria such as magnitudes, spectral classes, distance, etc.
The constellation where each star is located is listed by the standed three-letter abbreviation. In the Bright Star Catalog that is only true for those with Bayer or Flamsteed designations, which form only a small fraction of the catalog. This makes it easy to sort by constellation. Indeed, the order of the stars in the catalog is sorted first alphabetically by constellation and second by the star number assigned in the Bright Star Catalog (designated "HR", meaning "Harvard Revised"). Those numbers are very close to sorting by right ascension. This greatly facilitates finding a dim star in the catalog which has no other designation. Of course, one can easily resort the catalog to be in order of HR numbers if desired.
- Proper names of the brighter stars are included.
- There is an "ID" column which lists the star designation by either Bayer (Greek), Flamsteed, English letter, or HR number if there is no other. The Bright Star Catalog combines the first two into one column and does not have any English letter designations. This is especially important for the southern skies which Flamsteed could not see. Those stars mostly have English letter star designations which are not included in the Bright Star Catalog making it more difficult to locate them in a star atlas.
The "Parallax" column is replaced by a "Distance" (in light years) column, because determining distance is the main use of parallax.
Constellation numbers are also assigned to all 88 constellations. This is principally for the purpose of sorting. In my work it is desirable sometimes to study only the original 48 constellations, so they are numbered from 1 to 48. The zodiac constellations are numbered 1 to 12 so they can be sorted out easily. The numbering is done by sidereal longitude, which is defined to begin at zero at the star Pi Vir in the head of Virgo. That ties (ecliptic) longitude to the stars, not to the precessing earth. That star was chosen to best divide the zodiac into 30-degree sectors and it has very low proper motion which allows the longitudes of Ptolemy's star locations to be compared to modern day observations. Thus Virgo is constellation number 1 and Leo is number 12. The numbering continues in sets of 12 with each constellation assigned a number corresponding to the to the zodiac longitude sector in which it is located. That means that the remainder when divided by 12 indicates approximately what zodiac constellation it is above or below. One of the original 48 constellations was composed of stars in Canes Venatici and Coma Berenices, so those are numbered as sub-parts of the former Infant Prince constellation (known in Egypt and Persia). Moreover the four constellations of Carina, Puppis, Vela and Pyxis are numbered as sub parts of the original constellation Argo. Thus, the 88 modern constellations are numbered from 1 to 84, which conveniently happens to be a multiple of 12.
Sideral longitudes and latitudes are included, as just mentioned and as described more particularly in "Coordinates for the Constellations". They were calculated using a 2000.0 obliquity of the ecliptic (tilt of earth's axis to its orbital plane) of 23.43928°. Sidereal latitude is taken as identical to the usual celestial (ecliptic) latitude. Another purpose of sidereal coordinates is to be able to see an image of the map in the mind's eye just by knowing the longitude. In other words, it allows the phrase "Mars is 3 degrees into Leo" to mean something because when familiar with the system one knows where each zodiac 30-degree sector begins and ends. In fact, having visual markers of those sector boundaries was one of the criteria by which the zero point was chosen. Thus there is a column both for sidereal longitude from 0 to 360° and also from 1 to 30 in each zodiac sector. For example a sidereal longitude of 41 degrees would be 11 degrees into the second 30-degree sector and called 11 Lib for a zodiac longitude.
The HR number is listed in the first column so that this table can easily be inserted as a separate spreadsheet worksheet, such that the VLOOKUP function can easily access its columns for other worksheet usage.
To actually locate the stars in this catalog, it is usually necessary to look up their positions on a star map to see their positions relative to others in the sky. The spiral bound version of The Cambridge Star Atlas by Wil Tirion is recommended to be used in conjunction with these tables. The maps indicate not only the usual Bayer Greek letters and Flamsteed number designations, but also the upper and lower case English alphabet designations used extensively in the southern skies. The maps are also in color and lay flat with no stars lost in the binding. Moreover, it has the stick figure constellations figures drawn in which are extremely useful to find stars quickly, but which are not found in almost any other detailed star atlas. Other atlases are more like a map of the U.S.A. would be with only cities shown as dots without the outlines of the states drawn in.
Hopefully the Mag 5 Star Catalog will be useful to others doing star table analysis. It can be downloaded free by clicking the above "download" button. Then double click on the file, which should bring up your default spreadsheet program. Then select "comma" as the column separator. The columns are described in the table shown.