beluej123
commented
1 month ago I believe, if you remove the printing format info from utc_strftime(), you will get what you r looking for: change from: utc_strftime("%Y-%b-%d %H:%M:%S %Z") to: utc_strftime()
In particular, the formatting you are asking for includes %Z which is time-zone info, but the tt (i.e. Julian) output from sun_rise() and twilight_rise() does not have time-zone info. I do not have a clue why the utc_strftime(... %Z) outputs Central Standard Time...
Below are a couple other notes: If you wish to see how I get local time-zone date/time, I made a few adjustments to your code, shown below (note my variable ttr_local). I added a few comments to your code I thought may be helpful...
In my opinion, I think skyfield's time-zone doc's could use updates to show how to convert between time-zones. For example: (1) converting tt-time (Julian) to UTC (for user display) and any of the other defined time-zones, and (2) converting a user entered time (with time-zone) to a tt-time and display UTC. I realize it is useful that skyfield's doc's are mindful of backward compatibility since some users may still use the 3rd party package pytz. However, I think this is especially germane now that the pytz module is not recommended by the python doc's, because python 3.9+ has its own time-zone methods...
If you wish to see how I get local time-zone date/time, I made a few adjustments to your code, shown below.
"""
[skyfielders/python-skyfield] utc_strftime gives observers timezone (Issue #1006)
Explore skyfield functions:
(1) sunrise sunset
(2) in-progress, equinox; astronomical & local (approx. equilux)
(3) timezone conversions;
I think skyfield's timezone doc's could use updates
Notes:
----------
Sunrise/sunset angles (https://aa.usno.navy.mil/faq/RST_defs):
astronomical = +- 18deg
nautical twilight = +-12deg
civil twilight = +-6deg
sunrise sunset = 0deg
https://rhodesmill.org/skyfield/examples.html#dark-twilight-day-example
https://rhodesmill.org/skyfield/api-almanac.html
https://rhodesmill.org/skyfield/time.html
https://rhodesmill.org/skyfield/searches.html
https://www.timeanddate.com/astronomy/equilux.html
Returns
-------
None
"""
from zoneinfo import ZoneInfo
from skyfield import almanac
from skyfield.api import load, wgs84
def sun_rise(eph, observer, t0, t1):
f = almanac.find_risings(
target=eph["Sun"],
observer=observer,
start_time=t0,
end_time=t1,
)
return f
def twilight_rise(eph, observer, t0, t1, hor):
# c=civil, n=nautical, a=astronical
if hor == "c":
horizon = -6
elif hor == "n":
horizon = -12
elif hor == "a":
horizon = -18
f = almanac.find_risings(
target=eph["Sun"],
observer=observer,
start_time=t0,
end_time=t1,
horizon_degrees=horizon,
)
return f
# Load ephemeris data
eph = load("de440.bsp")
ts = load.timescale()
# Define location, US/central timezone
latitude = 41.7093
longitude = -86.8639
elev = 186.927 # Elevation in meters
loc = wgs84.latlon(latitude, longitude, elevation_m=elev)
observer = eph["Earth"] + loc
# Define the time for the date you want
t0 = ts.utc(2024, 9, 26)
t1 = ts.utc(2024, 9, 27)
# print date/time format
prt_t_fmt = "%Y-%b-%d %H:%M:%S" # %b = a 3 letter month
print(f"\nSunRise & timezone - github's KD9LWR issue #1006 (2024-09-26):")
print(f"Location: {loc}")
ttr = sun_rise(eph, observer, t0, t1) # returns tt time; no timezone info
print(f"sunrise : {ttr[0].utc_strftime()[0]}")
# convert sunrise to local time, requires either:
# python-zoneinfo import, or pytz module (3rd party)
ttr_local = ttr[0].astimezone(ZoneInfo('US/Central')) # cast to central time zone
print(f"sunrise, zone: {ttr_local[0].strftime(prt_t_fmt)} {ttr_local[0].tzname()}")
ttc = twilight_rise(eph, observer, t0, t1, "c")
print(f"civil : {ttc[0].utc_strftime()[0]}")
ttn = twilight_rise(eph, observer, t0, t1, "n")
print(f"nautical : {ttn[0].utc_strftime()[0]}")
tta = twilight_rise(eph, observer, t0, t1, "a")
print(f"astronomical : {tta[0].utc_strftime()[0]}")
brandon-rhodes
Skyfield function
utc_strftimegives observers timezone.Expected
Result
Version
My Code