Having writ, moving on (was Re: sexagesimal)

[Rob Seaman]

Hi Roy,

I admire your chutzpah, but the more fundamental the concept, the  
more painful its standardization.

There's more than a bit of virtual surreality in discussing third  
millennium A.D. support for a third millennium B.C. data  
representation.  For example, FITS may not have been codified by  
Hammurabi – it just feels that way.  Implicit in the original 1981  
Wells, et. al., paper was that angular values would be expressed in  
decimal degrees.  This has long since been relaxed (see, for example,  
http://listmgr.cv.nrao.edu/pipermail/fitsbits/2000-November/ 
000158.html) to allow sexagesimal strings for RA and DEC keywords.   
The point is not only that prior usage is hard to overcome – the  
point is that the entire focus on RA and DEC is a red herring, since  
the real issue is generalized WCS representations.

Similarly, that sexagesimal notation itself predates the code of  
Hammurabi (c. 1780 B.C.) by several centuries only begins to hint at  
the semantic inertia we're facing.  The core conceit of 2880 byte  
FITS records is the same as the reason for using base sixty numbers  
– easy divisibility into round fractions.  Minutes and seconds are  
often reported separately in the astronomical literature from hours  
or degrees because – well – that's the whole point.  It is an aid  
for reading tabular listings, for comparing nearby locations on the  
sky, for simplifying approximations, and to permit reliable  
transmission of numbers that would otherwise require double precision  
floats.

It may also be required by a journal's typographic conventions.  For  
instance, the RA and DEC values from the example FITS header in the  
1981 paper are in decimal degrees, 122.5419617 and 66.5995040 – but  
these are written in the text as:


Maybe the real IVOA argument is with the University of Chicago.

	The king cried aloud to bring in the astrologers,
	the Chaldeans, and the soothsayers.  And the
	king spake, and said to the wise men of Babylon,
	Whosoever shall read this writing, and shew me the
	interpretation thereof, shall be clothed with scarlet,
	and have a chain of gold about his neck,
	and shall be the third ruler in the kingdom.

When Daniel read the writing on the wall, base sixty notation had  
already been in use for sixty generations.

Rob

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