Year 2000

[Barry M. Schlesinger]

A few questions....

Arnold Rots <arots at xebec.gsfc.nasa.gov>, in the revised Year 2000 
Proposal includes

> 3.2) The new recommended format is a restricted subset of
>   ISO-8601, being one of two options:
>   a) 'CCYY-MM-DD'
>   b) 'CCYY-MM-DDThh:mm:ss[.sss...]'

>   <CCYY> represents a calendar year, <MM> the ordinal number of a calendar
>   month within the calendar year, and <DD> the ordinal number of a day
>   within the calendar month.  <hh> represents the hour in the day, <mm>
>   the minutes, <ss[.s...]> the seconds.  'T' is the time designator.

>   In the short form, there may not be any additional terminator/separator
>   (such as T).  In the long form, there must be a 'T' time designator
>   between the date and the time.
>   The decimal point character is an ASCII full-stop.
>   The number of decimal places in the `seconds' field may be arbitrarily 
>   long, up to the FITS header-card limitations.
 
Is the term "ASCII full-stop" universally understood?  Perhaps it 
would be useful to give the hexadecimal representation as well.

>                    4) Use of the DATE-OBS keyword
 
> 4.1) The name of the keyword shall remain DATE-OBS.
 
> 4.2) It is suggested that the DATE-OBS refer to the start of an observation.
>    This relationship should be clarified in the comment field.

> 4.3) The default interpretation of all DATExxxx keywords shall use the
>   Gregorian Calendar for the date portion.

> 4.4) The value of the DATExxxx keywords shall be expressed in the time
>   scale or time system that is dominant in the HDU.  The default
>   interpretation shall use UTC (for dates since 1972) or UT (for dates
>   before 1972).
 
In 4.4, which addresses the problems of files that mix time scales ... 
How does one determine or define which time system is dominant in the 
HDU?

Also, 4) has the title "Use of the DATE-OBS keyword" but addresses 
usage of other DATExxxx keywords in 4.3 and 4.4.  In the original 
proposal, it addressed only DATE-OBS.  So the title is somewhat 
inconsistent with the content.

				Barry Schlesinger
				FITS Support Office