[fpc-pascal] 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