Moon phase - time finder

[skynoob-new]

Hello ,
Using below code i can find the moon phase between days, given the time,

from skyfield import api
from skyfield import almanac
ts = api.load.timescale()
eph = api.load('de421.bsp')
t = ts.utc(2020,7, range(1,5))
for i in t:
  phase = almanac.moon_phase(eph, i)
  print('Moon phase: {:.1f} degrees'.format(phase.degrees),i)

I was searching for finding the time at which a specific moonphase will occur and i got this https://rhodesmill.org/skyfield/searches.html, i am not really sure how would i combine that here to find the time at which some of the moon phase occur, ex: at what time, the moon phase would be at 20 /40/60 degrees. It seems that i cannot send a list of dates to the function almanac.moon_phase. Any help would be appreciated.

[skynoob-new]

Any help on this would be appreciated

[skynoob-new]

@brandon-rhodes any help on this? i dont see to find a way to get out of this It seems that i cannot send a list of dates to the function almanac.moon_phase

[skynoob-new]

Traceback (most recent call last):
  File "E:/myfolder/Astronomynoobexplore/moon_phase.py", line 31, in <module>
    for ti, ei in zip(t, moonphase(t)):
  File "E:/myfolder/Astronomynoobexplore/moon_phase.py", line 19, in moonphase
    return  ('Moon phase: {:.1f} degrees'.format(phase.degrees))
TypeError: unsupported format string passed to numpy.ndarray.__format__

[brandon-rhodes]

Thank you for the full traceback! It looks like Skyfield isn't involved in that error? It looks like it involves the phase.degrees object and what the code is trying to do with the Python string .format() method; I'd suggest printing and inspecting the phase.degrees object, it's probably not something you can format that way.

[skynoob-new]

i got that from here,

https://rhodesmill.org/skyfield/almanac.html#phases-of-the-moon

[brandon-rhodes]

True, but in the example the line of code is applied to only a single phase value for a single date. Since you are giving it an array date instead, you should be getting an array back, which does not print the same way a single number prints. Again, I suggest printing and inspecting the phase.degrees object so that you can see more clearly what kind of value you are dealing with.

[skynoob-new]

you are right, i got it working. Thanks

[brandon-rhodes]

Try building a function that, instead of returning just True and False, returns an integer 0 or 1 or 2… depending on whether the angle is between 0° and 20°, or 20° and 40°, or 40° and 60°, and so forth. If you look at Skyfield's almanac.py, you'll see examples like seasons() and moon_phases() that use that approach:

https://github.com/skyfielders/python-skyfield/blob/master/skyfield/almanac.py#L59

Do you think the documentation at https://rhodesmill.org/skyfield/searches.html needs to be expanded to explain this approach?