Sun-Moon Ephemeris for Negative Years

Hi,

I am trying to produce Sun-Moon Ephemeris for Lunar Crescent Visibility Records. My code able to calculate the ephemeris correctly for modern Lunar Crescent Visibility, however when calculating the Babylonian data, my ephemeris unable to produce a accurate result.

Here is my some of my code.

#Find Sunset

def sunset(x):

    location = Topos(latitude_degrees=x['Lat'], longitude_degrees=x['Long'])
    t0 = ts.utc(x['Year'], x['Month'], x['Day'])
    t1 = ts.utc(x['Year'], x['Month'], x['Day']+1)
    f = almanac.risings_and_settings(eph, eph['Sun'], location)
    t, y = almanac.find_discrete(t0, t1, f)
    
   # print(x['Day'], x['Month'] ,x['Year'],x['Lat'],x['Long'])


    for ti, yi in zip(t, y):
        if yi == False:
            hsunset = ti.utc.hour
            msunset = ti.utc.minute
            ssunset = ti.utc.second
            str_sunset = str(hsunset)+":"+str(msunset)
            jd_sunset = float(format(ti.tai))
            t = ts.tt_jd(float(jd_sunset))
            t = ts.tt_jd(float(jd_sunset))
            u=t.utc_iso()

            return str_sunset
        else:
            None
    print(t)

df['Sunset'] = df.apply(sunset, axis=1)

df

And here is my result Ephemeris, notice that the Data for Negative years is not accurate.

No     Day	Month	Year	Lat	Long	Ele	V	M	Sunset	Moonset	lagtime	Moonage	ArcV	DAZ	Width in Arc Second	ArcL
0	1	7	1973	-44.0	170.5	1189	V	B	5:8	5:58	50.0	17.49	6.28	6.35	7.285310	9.614935
1	29	1	1922	-33.9	18.5	30	I	I	17:52	18:32	40.0	42.08	7.34	17.13	9.821328	19.025304
2	28	2	1922	-33.9	18.5	30	V	N	17:23	18:11	48.0	46.60	9.06	18.07	12.930653	20.586570
3	29	3	1922	-33.9	18.5	30	I	I	16:44	17:19	35.0	27.70	6.10	10.01	5.599340	12.263027
4	10	7	-368	32.6	44.4	15	V	N	20:18	0:22	-677.0	158.98	44.20	212.45	161.990073	138.158263
5	19	7	-73	32.6	44.4	15	V	N	19:14	21:19	-847.0	100.91	24.90	185.97	2.697795	174.003688
6	20	7	-179	32.6	44.4	15	V	N	19:33	22:29	-876.0	116.53	35.19	179.64	18.775558	179.717161
7	23	7	-372	32.6	44.4	15	V	N	20:14	23:39	-764.0	150.94	35.24	197.62	29.737782	159.553862
8	23	7	-87	32.6	44.4	15	V	N	19:14	21:44	-870.0	83.59	29.75	180.57	1.432747	178.656614
9	29	7	-307	32.6	44.4	15	V	N	19:54	2:1	-468.0	240.22	30.09	255.21	444.171906	99.947300

I have check the Data with the literature. All of the Ephemeris for positive year is correct while ephemeris for negative year is incorrect. I am using de422.bsp for this calculation.

Greatly appreciate for help. Been stuck here for days. Thanks!

[brandon-rhodes]

Without any examples of the dates from the literature, I won’t be able to make specific comments, since I cannot see how big the differences are between the literature and your own data.

But — have you read the Skyfield documentation on dates? Your code makes no mention of the Julian calendar, and if the literature used that calendar instead of our modern one, the dates will not match:

https://rhodesmill.org/skyfield/time.html#ancient-and-modern-dates

[brandon-rhodes]

I’m glad it’s working now!