On Jan 26, 2015, at 12:21 PM, Warner Losh <[email protected]> wrote:

> It all depends on the data that you are using whether the new day starts at 
> midnight
> or noon. If you are talking to astronomers before the 20th century, chances 
> are good
> it is noon.

Big fan of Patrick O'Brian.  Frequent mention is made in his Nelson-era novels 
of their taking noon sightings of the Sun and declaring the start of a new day. 
 I don't recall any discussion of mean versus apparent time, however, though 
the ships' chronometers are often referred to.

> Civil folks chances are it is midnight. This ambiguity is why insurance 
> companies
> say that something runs from 12:01am or 11:59pm or some other time that’s 
> unambiguous.

Of course ante and post meridiem also reference the Sun.  Perhaps make that 
"currently unambiguous" ;-)

Rob

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