#?-*-?coding:utf-8?-*-
“““Functions?for?converting?between?Julian?dates?and?calendar?dates.

A?function?for?converting?Gregorian?calendar?dates?to?Julian?dates?and
another?function?for?converting?Julian?calendar?dates?to?Julian?dates
are?defined.?Two?functions?for?the?reverse?calculations?are?also
defined.

Different?regions?of?the?world?switched?to?Gregorian?calendar?from
Julian?calendar?on?different?dates.?Having?separate?functions?for?Julian
and?Gregorian?calendars?allow?maximum?flexibility?in?choosing?the
relevant?calendar.

All?the?above?functions?are?“proleptic“.?This?means?that?they?work?for
dates?on?which?the?concerned?calendar?is?not?valid.?For?example
Gregorian?calendar?was?not?used?prior?to?around?October?1582.

Julian?dates?are?stored?in?two?floating?point?numbers?（double）.??Julian
dates?and?Modified?Julian?dates?are?large?numbers.?If?only?one?number
is?used?then?the?precision?of?the?time?stored?is?limited.?Using?two
numbers?time?can?be?split?in?a?manner?that?will?allow?maximum
precision.?For?example?the?first?number?could?be?the?Julian?date?for
the?beginning?of?a?day?and?the?second?number?could?be?the?fractional
day.?Calculations?that?need?the?latter?part?can?now?work?with?maximum
precision.

A?function?to?test?if?a?given?Gregorian?calendar?year?is?a?leap?year?is
defined.

Zero?point?of?Modified?Julian?Date?（MJD）?and?the?MJD?of?2000/1/1
12:00:00?are?also?given.

This?module?is?based?on?the?TPM?C?library?by?Jeffery?W.?Percival.?The
idea?for?splitting?Julian?date?into?two?floating?point?numbers?was
inspired?by?the?IAU?SOFA?C?library.

:author:?Prasanth?Nair
:contact:?prasanthhn@gmail.com
:license:?BSD?（https://opensource.org/licenses/bsd-license.php）
“““
from?__future__?import?division
from?__future__?import?print_function
import?math

__version__?=?“1.4.1“

MJD_0?=?2400000.5
MJD_JD2000?=?51544.5


def?ipart（x）:
????“““Return?integer?part?of?given?number.“““
????return?math.modf（x）[1]


def?is_leap（year）:
????“““Leap?year?or?not?in?the?Gregorian?calendar.“““
????x?=?math.fmod（year?4）
????y?=?math.fmod（year?100）
????z?=?math.fmod（year?400）

????#?Divisible?by?4?and
????#?either?not?divisible?by?100?or?divisible?by?400.
????return?not?x?and?（y?or?not?z）


def?gcal2jd（year?month?day）:
????“““Gregorian?calendar?date?to?Julian?date.

????The?input?and?output?are?for?the?proleptic?Gregorian?calendar
????i.e.?no?consideration?of?historical?usage?of?the?calendar?is
????made.

????Parameters
????----------
????year?:?int
????????Year?as?an?integer.
????month?:?int
????????Month?as?an?integer.
????day?:?int
????????Day?as?an?integer.

????Returns
????-------
????jd1?jd2:?2-element?tuple?of?floats
????????When?added?together?the?numbers?give?the?Julian?date?for?the
????????given?Gregorian?calendar?date.?The?first?number?is?always
????????MJD_0?i.e.?2451545.5.?So?the?second?is?the?MJD.

????Examples
????--------
????>>>?gcal2jd（200011）
????（2400000.5?51544.0）
????>>>?2400000.5?+?51544.0?+?0.5
????2451545.0
????>>>?year?=?[-46