我刚刚仔细阅读了《天文年历解释补编》的第11.2.3节,并尝试将其转化为Skyfield Python代码。以下是我的成果:
import numpy as np
from skyfield.api import load
from skyfield.constants import ERAD
from skyfield.functions import angle_between, length_of
from skyfield.searchlib import find_maxima
eph = load('de421.bsp')
earth = eph['earth']
moon = eph['moon']
sun = eph['sun']
def f(t):
e = earth.at(t).position.au
s = sun.at(t).position.au
m = moon.at(t).position.au
return angle_between(s - e, m - e)
f.step_days = 5.0
ts = load.timescale()
start_time = ts.utc(2019, 1, 1)
end_time = ts.utc(2020, 1, 1)
t, y = find_maxima(start_time, end_time, f)
e = earth.at(t).position.m
m = moon.at(t).position.m
s = sun.at(t).position.m
solar_radius_m = 696340e3
moon_radius_m = 1.7371e6
pi_m = np.arcsin(ERAD / length_of(m - e))
pi_s = np.arcsin(ERAD / length_of(s - e))
s_s = np.arcsin(solar_radius_m / length_of(s - e))
pi_1 = 0.998340 * pi_m
sigma = angle_between(s - e, e - m)
s_m = np.arcsin(moon_radius_m / length_of(e - m))
penumbral = sigma < 1.02 * (pi_1 + pi_s + s_s) + s_m
partial = sigma < 1.02 * (pi_1 + pi_s - s_s) + s_m
total = sigma < 1.02 * (pi_1 + pi_s - s_s) - s_m
mask = penumbral | partial | total
t = t[mask]
penumbral = penumbral[mask]
partial = partial[mask]
total = total[mask]
print(t.utc_strftime())
print(0 + penumbral + partial + total)
它会生成一个向量,其中包含月食发生的时间,以及总月食程度的评级:
['2019-01-21 05:12:51 UTC', '2019-07-16 21:31:27 UTC']
[3 2]
它的月食时间与NASA的大型月球历表中给出的时间相差不超过3秒:
https://eclipse.gsfc.nasa.gov/5MCLE/5MKLEcatalog.txt