[docs] Definition of Julian day

[Laura Hinkelman]

Hi,

On your documentation web page

  https://docs.python.org/2/library/time.html

it says:

  The Julian day *n* (1 <= *n* <= 365). ....

Despite common usage, what you are defining is the day of the year, not the
"Julian day."  Julian time is a complete time/date definition system based
on a reference time of noon Universal Time on January 1, 4713 BC (on the
Julian calendar).  This system originates in the astronomical community.
(See references below.) I'm really surprised that there aren't native
Python functions to convert in and out of Julian time, given that there are
plenty of astronomers writing code in Python.  Anyway, you might want to
write "day of year, sometimes (erroneously) referred to as Julian day," or
something like that.

https://aa.usno.navy.mil/data/docs/JulianDate.php
https://en.wikipedia.org/wiki/Julian_day

Along the same lines, I think it's silly to use a start year of 1970 for
your time reference, even if that's a UNIX convention.  A few things we
care about happened before 1970 -- and a few more will happen after 2038.
Hard endpoints are incredibly limiting.  This is why Matlab defines a
reference date of Jan. 1, 0000, and other people use Julian time, which has
an admittedly bizarre reference time.

Thanks,

Laura H.
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