How to compute Ascension / Descension cycle of the Moon

Question

I am struggling to find out an information about how to determine ascending/descending cycle of the Moon.

I can find from this source and a bunch of others, that Moon begins to descend when reaches Gemini and minimum when reaches Sagittarius.

I tried to do a simple comparison using flatlib library:

from flatlib import const
from flatlib.datetime import Datetime
from flatlib.geopos import GeoPos
from flatlib.chart import Chart

d1 = Datetime("2020/1/21")
d2 = Datetime("2020/1/22")
d3 = Datetime("2020/1/23")
pos = GeoPos('50n06', '14e24') #I concentrate to a specific place on northern hemisphere
c1 = Chart(d1, pos)
c2 = Chart(d2, pos)
c3 = Chart(d3, pos)

m1 = c1.get(const.MOON)
m2 = c2.get(const.MOON)
m3 = c3.get(const.MOON)
print(m1)
print(m2)
print(m3)

Which prints:

Moon Sagittarius +14:07:19 +13:16:13
Moon Sagittarius +27:17:06 +13:03:28
Moon Capricorn +10:14:25 +12:51:13

Am I right that moon is ascending during these days (21-23rd Jan 2020) as it moves from Sagittarius to Capricorn and further to Gemini?

I am aware of this answer, but I am not exactly sure if it deals with same problematics.

Answer 1

Thank you for your guiding comments. Compute Moon's declination and searching for Moon to begin ascend/descend can be quite easily achieved though skyfield API so I am posting some starter python code here:

from calendar import monthrange 
from skyfield.api import load

planets = load('de431_part-2.bsp') 
earth, moon = planets['earth'], planets['moon']

ts = load.timescale() 
year, month = 2020, 1 

for day in range(1, monthrange(year, month)[1] + 1):
    this_day = ts.utc(year, month, day)
    ra, dec, dist = earth.at(this_day).observe(moon).radec()
    print(this_day.utc_strftime('%Y-%m-%d %H:%M'), '    ', dec)

which yields Moon's declinations through January 2020 in degrees or radians:

2020-01-01 00:00      -10deg 04' 51.8" 
2020-01-02 00:00      -05deg 39' 57.1" 
2020-01-03 00:00      -01deg 02' 59.5" 
2020-01-04 00:00      +03deg 37' 53.6" 
2020-01-05 00:00      +08deg 14' 18.8" 
2020-01-06 00:00      +12deg 36' 35.0" 
2020-01-07 00:00      +16deg 32' 47.3" 
2020-01-08 00:00      +19deg 48' 21.8" 
2020-01-09 00:00      +22deg 06' 43.7" 
2020-01-10 00:00      +23deg 11' 39.4"  -> begins to descend
2020-01-11 00:00      +22deg 51' 15.5" 
2020-01-12 00:00      +21deg 02' 03.9" 
2020-01-13 00:00      +17deg 50' 48.5" 
2020-01-14 00:00      +13deg 32' 46.2" 
2020-01-15 00:00      +08deg 27' 58.8" 
2020-01-16 00:00      +02deg 57' 34.2" 
2020-01-17 00:00      -02deg 38' 26.5" 
2020-01-18 00:00      -08deg 01' 50.7" 
2020-01-19 00:00      -12deg 56' 07.5" 
2020-01-20 00:00      -17deg 06' 14.0" 
2020-01-21 00:00      -20deg 18' 51.8" 
2020-01-22 00:00      -22deg 23' 29.7" 
2020-01-23 00:00      -23deg 13' 57.4"  -> begins to ascend
2020-01-24 00:00      -22deg 49' 43.7" 
2020-01-25 00:00      -21deg 16' 03.0" 
2020-01-26 00:00      -18deg 42' 36.5" 
2020-01-27 00:00      -15deg 21' 24.7" 
2020-01-28 00:00      -11deg 24' 47.8" 
2020-01-29 00:00      -07deg 04' 09.9" 
2020-01-30 00:00      -02deg 29' 33.7" 
2020-01-31 00:00      +02deg 10' 07.1"