Re: "A diagram of C23 basic types"

On 29.04.2025 05:34, James Kuyper wrote:

On 4/28/25 20:10, Janis Papanagnou wrote:

[...]
>
And "seconds since midnight" where taken despite the Julian Dates
have a day start at high noon (12:00)? [*]

 
Strictly speaking, "Julian Day" is the number of days since Jan 01 4713
BCE at Noon (a date that was chosen because it simplifies conversion
between several different ancient calendar systems. It starts at Noon
because it was devised for use by astronomers, who are generally awake
at midnight and asleep at Noon (especially in ancient times).
 
Informally speaking, "Julian Day" is commonly used to refer to any
system for designating dates that include a "day of year" component, as
does the above example. Most of these start at midnight, not Noon.
 
There's no use being a purist about this (that would be my preference
too) - the informal meaning is quite common, probably more common than
the "correct" one.

In my language domain we have terms like "Modified Julian Date"
(MJD) that relate to the Julian Date according to the formula
  MJD = JD - 2'400'000.5
But as Keith mentioned the terms seem not be used consistently.

Janis