why the 0.5 in the Unix Epoch (for UnixToDateTime function)

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why the 0.5 in the Unix Epoch (for UnixToDateTime function)

Dennis
I just noticed that the definition of the constants have 0.5 in it.
Why?


from dateh.inc
const
    JulianEpoch = TDateTime(-2415018.5);

    UnixEpoch = JulianEpoch + TDateTime(2440587.5);


Dennis
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Re: why the 0.5 in the Unix Epoch (for UnixToDateTime function)

Vojtěch Čihák

Hi,

 

wiki https://en.wikipedia.org/wiki/Julian_day says that "... Julian day number 0 assigned to the day starting at noon on January 1, 4713 BC, ..."

The noon means 0,5.

 

V.

______________________________________________________________

> Od: Dennis <[hidden email]>
> Komu: FPC-Pascal users discussions <[hidden email]>
> Datum: 01.08.2017 13:14
> Předmět: [fpc-pascal] why the 0.5 in the Unix Epoch (for UnixToDateTime function)
>

I just noticed that the definition of the constants have 0.5 in it.
Why?


from dateh.inc
const
   JulianEpoch = TDateTime(-2415018.5);

   UnixEpoch = JulianEpoch + TDateTime(2440587.5);


Dennis
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Re: why the 0.5 in the Unix Epoch (for UnixToDateTime function)

Vojtěch Čihák
In reply to this post by Dennis

Hi,

 

wiki https://en.wikipedia.org/wiki/Julian_day says that "... Julian day number 0 assigned to the day starting at noon on January 1, 4713 BC, ..."

The noon means 0,5.

 

V.

______________________________________________________________

> Od: Dennis <[hidden email]>
> Komu: FPC-Pascal users discussions <[hidden email]>
> Datum: 01.08.2017 13:14
> Předmět: [fpc-pascal] why the 0.5 in the Unix Epoch (for UnixToDateTime function)
>

I just noticed that the definition of the constants have 0.5 in it.
Why?


from dateh.inc
const
   JulianEpoch = TDateTime(-2415018.5);

   UnixEpoch = JulianEpoch + TDateTime(2440587.5);


Dennis
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Re: why the 0.5 in the Unix Epoch (for UnixToDateTime function)

Dennis Poon


Vojtěch Čihák wrote:
>
> Hi,
>
> wiki https://en.wikipedia.org/wiki/Julian_day says that "... Julian
> day number 0 assigned to the day starting at noon on January 1, 4713
> BC, ..."
>
> The noon means 0,5.
>
Thanks,
that is a weird definition though IMHO.

Dennis
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Re: why the 0.5 in the Unix Epoch (for UnixToDateTime function)

Mark Morgan Lloyd-5
On 01/08/17 12:15, Dennis Poon wrote:
> Vojtěch Čihák wrote:>> Hi,>> wiki
> https://en.wikipedia.org/wiki/Julian_day says that "... Julian > day
> number 0 assigned to the day starting at noon on January 1, 4713 > BC,
> ...">> The noon means 0,5.>Thanks,that is a weird definition though IMHO.

Astronomer's convention.

--
Mark Morgan Lloyd
markMLl .AT. telemetry.co .DOT. uk

[Opinions above are the author's, not those of his employers or colleagues]
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Re: why the 0.5 in the Unix Epoch (for UnixToDateTime function)

Paul Nance
In reply to this post by Dennis
Actually the Julian calendar started at noon, the 0.5 is added to get to midnight. The Julian calendar was developed for astronomers, who view the sky when it gets dark and want all observing to be referenced to the same date. Us normal people start our day at midnight so we have to add the extra half day.  --  Paul

On Aug 1, 2017 7:14 AM, "Dennis" <[hidden email]> wrote:
I just noticed that the definition of the constants have 0.5 in it.
Why?


from dateh.inc
const
   JulianEpoch = TDateTime(-2415018.5);

   UnixEpoch = JulianEpoch + TDateTime(2440587.5);


Dennis
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