Terminology: "modified Julian day"

Jon Zeppieri zeppieri at gmail.com
Fri Aug 29 00:09:17 CDT 2014

At [http://www.unicode.org/reports/tr35/tr35-35/tr35-dates.html#Date_Field_Symbol_Table],
the documentation for the 'g' date pattern reads:

"Modified Julian day. This is different from the conventional Julian
day number in two regards. First, it demarcates days at local zone
midnight, rather than noon GMT. Second, it is a local number; that is,
it depends on the local time zone. It can be thought of as a single
number that encompasses all the date-related fields."

Based on this (and the accompanying example "2451334"), it looks like
this is different from the usual definition of "modified Julian day,"
which is (JD - 2400000.5). What's described in the documentation
sounds more like a Julian day number. (Though some people use "Julian
day number" to denote the day-of-year.)

I'd like to verify that the 'g' pattern is not supposed to produce (JD
- 2400000.5). If that's the case, I suggest that the documentation
change the terminology to avoid confusion with standard usage of
"modified Julian day".


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