Javascript or Python - How do I figure out if it's night or day?

geolocation, javascript, python, timezone

Solution

Note to Python 3 users: I just tried the code below using Python 3.8.6 and it works in that version, too. I had to convert the `print` statements into `print()` function calls, but that was all.

I noticed that the example implementation of `tzinfo` classes is different from what's in the Python 2 documentation, but using the example `tzinfo` classes in the tzinfo_example.py file referenced in the latest documentation worked just fine (but so did the older 2.x versions).

You can download a Python 3 version of the `sunriseset.py` file shown below from here.

You can do as I did and use this public domain Sun.py module to compute the position of the sun relative to positions on the Earth. (Warning: it contains tab characters and assumes tabs are every 8 characters.) It's pretty old, but has continued to work well for me for many years. I made a few superficial modifications to it to be more up-to-date with Python 2.7, such as making the few classes in it new-style, but for the most part it's unchanged.

Here's one module I created, called `sunriseset.py`, which shows how to use it to calculate the sunrise and sunset times for a specific location given its geographic coordinates and timezone. The referenced `timezone` module is an implementation of the `tzinfo` abstract base class described in the `datetime` module's documentation on `tzinfo`objects.

# -*- coding: iso-8859-1 -*-
import datetime
import timezone  # concrete tzinfo subclass based on the Python docs
import math
from Sun import Sun

__all__ = ['getsuninfo', 'Place']

class Place(object):
    def __init__(self, name, coords, tz=timezone.Pacific):
        self.name = name        # string
        self.coords = coords    # tuple (E/W long, N/S lat)
        self.tz = tz            # tzinfo constant

def _hoursmins(hours):
    """Convert floating point decimal time in hours to integer hrs,mins"""
    frac,h = math.modf(hours)
    m = round(frac*60, 0)
    if m == 60: # rounded up to next hour
        h += 1; m = 0
    return int(h),int(m)

def _ymd(date):
    """Return y,m,d from datetime object as tuple"""
    return date.timetuple()[:3]

def getsuninfo(location, date=None):
    """Return local datetime of sunrise, sunset, and length of day in hrs,mins)"""
    if date == None:
        querydate = datetime.date.today()
    else: # date given should be datetime instance
        querydate = date

    args = _ymd(querydate) + location.coords
    utcrise, utcset = Sun().sunRiseSet(*args)
    daylength = Sun().dayLength(*args)
    hrs,mins = _hoursmins(daylength)

    risehour, risemin = _hoursmins(utcrise)
    sethour, setmin   = _hoursmins(utcset)

    # convert times to timedelta values (ie from midnight utc of the date)
    midnight = datetime.datetime(tzinfo=timezone.utc, *_ymd(querydate))
    deltarise = datetime.timedelta(hours=risehour, minutes=risemin)
    utcdatetimerise = midnight+deltarise
    deltaset = datetime.timedelta(hours=sethour, minutes=setmin)
    utcdatetimeset  = midnight+deltaset

    # convert results from UTC time to local time of location
    localrise = utcdatetimerise.astimezone(location.tz)
    localset  = utcdatetimeset.astimezone(location.tz)

    return localrise, localset, hrs, mins

if __name__ == "__main__":
    import datetime, timezone

    def unittest(location, testdate):
        risetime, settime, hrs, mins = getsuninfo(location, testdate)

        print "Location:", location.name
        print "Date:", testdate.strftime("%a %x")
        print risetime.strftime("Sunrise %I:%M %p"), settime.strftime("- Sunset %I:%M %p (%Z)")
        print "daylight: %d:%02d" % (hrs,mins)
        print

    place = Place("My House", (-121.990278, 47.204444), timezone.Pacific)

    # test dates just before and after DST transitions
    print "pre 2007"
    print "========="
    unittest(place, datetime.date(2006, 4, 1))
    unittest(place, datetime.date(2006, 4, 2))
    unittest(place, datetime.date(2006, 10, 28))
    unittest(place, datetime.date(2006, 10, 29))

    print "2007"
    print "========="
    unittest(place, datetime.date(2007, 3, 10))
    unittest(place, datetime.date(2007, 3, 11))
    unittest(place, datetime.date(2007, 11, 3))
    unittest(place, datetime.date(2007, 11, 4))

Problem

any idea how I figure out if it's currently night/day or sunrise/dawn based on time and location of the user? I haven't found anything useful that I could use within either the client or backend. What makes it tricky is the hour doesn't necessarily define if it is night and day, this depends pretty much on the year, month, day, hour and geo coordinates. For clarification... to emulate something like this. A way to approximate this would be very useful as well. Hope that someone can help!

Original source

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