Standards for Astronomical Catalogues, Version 2.0 (pdf)
(February 2000)

3.3 Labels

Conventions used for some labels

 
Symbol  Explanation  Default Limits 
RAh  Part of the right ascension expressed in hours   [0,24[ 
RAm  Part of the right ascension expressed in minutes  [0,60[
RAs  Part of the right ascension expressed in seconds  [0,60[
RAdeg  Right ascension expressed in decimal degrees 
	(Alternative: 	RAhms could be envisaged for a right ascension expressed
	in sexagesimal with no embedded blanks and leading zeroes, RAbhms
	for sexagesimal values with embedded blanks.
	Such extensions would however require special interpretation by
	FITS readers.
	)
	                                                    [0,360[
RArad  Right ascension expressed in radians  [0,2π[
RAsec  Right ascension expressed in seconds  [0,86400[
DE-  Sign of declination  [+-] 
DEd  Part of the declination expressed in  degrees [0,90]
DEm  Part of the declination expressed in  arc minutes [0,60[
DEs  Part of the declination expressed in  arc seconds [0,60[ 
DEdeg  Declination expressed in decimal degrees 
    (Alternative: 	DEdms could be envisaged for a declination expressed
	in sexagesimal with no embedded blanks and leading zeroes, DEbdms
	for sexagesimal values with embedded blanks; questions similar to the
	RAhms note have to be addressed.
	)
	                                                [–90,+90]
DErad  Declination expressed in radians  
		[–π/2,+π/2]
DEsec  Declination expressed in arcsec [–324000,+324000]
PosErr  Position mean error	 >=0 
dRA  dDE   Difference in Right Ascension or Declination   
oRA  oDE   Offset  from a reference position in R.A. or Dec. 
ELON  ecliptic longitude  [0,360[ 
ELAT  ecliptic latitude  [–90,+90] 
GLON  galactic longitude  [0,360[ 
GLAT  galactic latitude  [–90,+90 
Epoch  Epoch — write Ep-1900 for a year with 1900 offset  
plx  Parallax 
pmRA  Proper motion in Right Ascension 
pmDE  Proper motion in Declination 
pmX  Proper motion along X direction  
Seq  a Sequential number used e.g. to number the objects  
Name  the main name of an object or feature    
Diam  Diameter – or MajDiam and MinDiam   >=0 
Axis  Half Diameter – also MajAxis and MinAxis   >=0 
PA  Position Angle, normally North to East  [0,360[ 
Rad  Radius   >=0 
HRV  Heliocentric Radial velocity 
RVel  Radial velocity 
Sep  Separation (anglular or linear)  >=0 
SpType  Spectral type 
MType  Morphological type 
Vmag  Magnitude (apparent) in V filter 
VMag  Absolute Magnitude in V filter 
Kmag  Magnitude (apparent) in K filter ...

Sp+Index  Spectral index (α in relation S(ν) = ν^α) 
Sp-Index  Spectral index (α in relation 
	S(ν) = ν^–α) 
BibCode  The 19-digit 
        bibcode 
Text  Free-format text like list of authors, titles...

Remember that a label is always a single word: it cannot contain any embedded blank or space. Other characters are in principle accepted, e.g. parentheses or other punctuation signs, with the following restrictions:

the characters $ @ ! ` \ ^ ~ & are not accepted in a label
the first character of a label can't be one of the symbols + - * / = . # _ ' "
the last character of a label can't be one of the symbols , ;
the various kinds of parentheses and brackets ( ) [ ] { }, when used, must be balanced
a label can't be made of digits only
a single-character label must be alphabetic.
the label — is used for filling bytes, like the colon fond sometimes between the hours and minutes, or a x existing between the major and minor axises of a galaxy.

Some commonly used labels are presented in label. This table is not an exhaustive list of all possible column labels; it merely represents the standards adopted for the most common columns headings — like celestial coordinates, times and dates, and some of the most frequently found parameters. The VizieR service contains all definitions of all colums; these definitions are stored in the METAcol (field meta-data) table which can be queried like any of the tables accessible in VizieR. For instance, finding the columns having oscillator strength in their explanation can be found by entering the constraint *oscillator strength* (the * matches any number of characters) in the explain field of the METAcol

Some comments on the labels defined in label:

unicity principle: two columns can't have the same label in a table (the — label however can be present several times). When a table contains for instance the equatorial position in two different systems, B1950 and J2000, choose the labels RAh ...DEs for the basic (original) position, and choose another set of names, e.g. RA1950h ...DE1950s for the other set of positions.
Julian dates should be complete – no truncated Julian date, no Modified Julian Date (MJD) which are the source of many confusions.

The following suffixes can be appended to a label to designate the components of time or angle:

	.Y  Year part (in order to avoid any ambiguity,
		the year should include all 4 digits) 
	.M  Month name or number in range [1⋅⋅⋅12] 
	.D  Day number in month 
		(2 digits, range [1⋅⋅⋅31]) or 
		year (3 digits, range [1⋅⋅⋅366])
	.h  Hour (range [0⋅⋅⋅24[) 
	.m  Minutes (range [0⋅⋅⋅60[)) 
	.s  Seconds (range [0⋅⋅⋅60[)) 
	.d  Degrees (range [0⋅⋅⋅360[)

For instance, the various components of an observation date and time can be labelled Obs.Y, Obs.Y, Obs.M, Obs.D, Obs.h, Obs.m.

remember that labels are normally written at the top of each column; very long names should be avoided, especially for short (a couple of bytes) columns
... but names should however not be too cryptic !
Columns containing file names should contain file or File in their labels – e.g. FITSfile to indicate an associated image in FITS format

A parameter has frequently associated values, and we have adopted the rule of association with the one-letter-underscore prefix: if a column is obviously associated to another one — typically mean errors or uncertainty flags — we use one of the underscore prefixes listed in prefix.

Conventions used for label prefixes

 
Symbol  Explanation  Default Limits  
a_label  aperture used for
		parameter label  >=0 
B_label  for an upper bound (maximal value)
		on  parameter label 
b_label  for a lower bound (minimal value)
		on  parameter label 
D_label  for a difference (Δ)
		on  parameter label (e.g. (O-C) 
d_label  for a number of degrees of freedom
		or for number of digits on 
		parameter label  >0 
E_label  mean error (upper limit) 
		on parameter label 		 >=0 
e_label  mean error (σ) 
		on parameter label  >=0 
f_label  flag
		on parameter label   
L_label  Likelihood  
		on parameter label  
l_label  limit flag  
		on parameter label  [<>]
m_label  multiplicity index  
		on parameter label to resolve ambiguities  
n_label  note (remark) 
		on parameter label  
o_label  number of observations 
		on parameter label  >=0 
q_label  quality 
		on parameter label  
r_label  reference (source) for parameter label  
s_label  dispersion (σ) 
		on parameter label (the σ of a mean of N values
		is asymptotically equal to the dispersion divided by 
		sqrt(N)) >=0 
u_label  uncertainty flag 
		on parameter label  [ :] 
w_label  weight  of parameter label  >=0 
x_label  unit in which parameter label is
	expressed

Usual mathematical functions may be specified in the label, with parentheses or a dot; for instance, the logarithm of the effective temperature could be labelled log(Te) or log.Te.

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Standards for Astronomical Catalogues, Version 2.0 (pdf)(February 2000)

3.3 Labels

Standards for Astronomical Catalogues, Version 2.0 (pdf)
(February 2000)