New Moon error (ΔT?)

[miccomte]

Hi all,
I am writting a SW to display the dates of the phases of the moon in ancient time, but I have an error when I compare my results to the NASA's numbers, this error is increasing the further I do from present time. It looks to me that somehow ΔT is not applied. How can I check this?

Here are my results:
Output of my software :
New moon: 2020-01-24 at 21:41:59
New moon: 1600-01-16 at 05:07:03
New moon: 1 (Julian)-01-13 at 13:57:55
New moon: Year -241 (Julian)-01-19 at 17:45:13
In "Six Millennium Catalog of Phases of the Moon":
Year 2020 New Moon Jan 24 21:42
Year 1600 New Moon Jan 16 05:06
Year 1 New Moon Jan 13 10:58
Year -0241 New Moon Jan 19 13:59

And I made a test with this code:
t_test = ts.utc(-241, 4, 15) # Your test date
print(f"Skyfield ΔT: {t_test.delta_t} seconds")
exit()

I have this result, which seems to correspond to the difference:
Skyfield ΔT: 13294.066568561888 seconds

Process finished with exit code 0

[brandon-rhodes]

Output of my software :
New moon: 2020-01-24 at 21:41:59

Could you share the code you use to display this date, so we can see which timescale you are using?