Can't get dawn at this location on this day

[nhoover]

from astral import LocationInfo
from zoneinfo import ZoneInfo
from datetime import datetime

# Here is a problematic location in Mongolia
z = ZoneInfo('Asia/Ulaanbaatar')
p = LocationInfo('x', 'x', 'Asia/Ulaanbaatar', 46.79, 101.95)

year = 2025
month = 2

for day in [4, 5, 6]:
    print(f'{year}-{month}-{day}: Sunrise {sunrise(p.observer, datetime(year,month,day).astimezone(z), tzinfo=z)}')
    try:
        print(f'{year}-{month}-{day}: Dawn    {dawn(p.observer, datetime(year,month,day).astimezone(z), tzinfo=z)}')
    except ValueError:
        print(f'Could not get dawn for {year}-{month}{day}')```

Produces this with Astral 3.2 and Python 3.13.1:

2025-2-4: Sunrise 2025-02-04 08:33:09.401354+08:00
2025-2-4: Dawn    2025-02-04 08:00:23.477507+08:00
2025-2-5: Sunrise 2025-02-05 08:31:48.131147+08:00
Could not get dawn for 2025-25
2025-2-6: Sunrise 2025-02-06 08:30:25.162764+08:00
2025-2-6: Dawn    2025-02-06 07:57:50.427476+08:00

There's nothing special I can see about this position or these days. 

Also check out Feb 25. But all the rest of the days of the year look fine.

[nhoover]

Here's another one:

# Here's a problematic place in Norway, just above the Arctic circle
z = ZoneInfo('Europe/Oslo')
p = LocationInfo('x', 'x', 'Europe/Oslo', 67.88, 12.98)
print(f'\n{p}')

year = 2025
month = 5
for day in [21, 22, 23, 24, 25, 26]:
    try:
        print(f'{year}-{month:02}-{day:02}: Sunrise {sunrise(p.observer, datetime(year,month,day).astimezone(z), tzinfo=z)}')
    except ValueError:
        print(f'Could not get Sunrise for {year}-{month:02}-{day:02}')

LocationInfo(name='x', region='x', timezone='Europe/Oslo', latitude=67.88, longitude=12.98)
2025-05-21: Sunrise 2025-05-21 02:21:42.785710+02:00
2025-05-22: Sunrise 2025-05-22 02:14:41.780903+02:00
2025-05-23: Sunrise 2025-05-23 02:07:08.157144+02:00
Could not get Sunrise for 2025-05-24
2025-05-25: Sunrise 2025-05-25 01:49:10.855431+02:00
2025-05-26: Sunrise 2025-05-26 01:37:18.380089+02:00

The value for sunrise for 05-24 should be something between the values for the surrounding days.