# What is precision of planet periods data?

Wikipedia gives $$10759.22$$ days for sidereal period of Saturn. I have calculated a period from de441_part-1.bsp and obtained $$10736.247\bar{2}$$ days. Why such a big difference? Which is more accurate? What accuracy in percentage I can expect from periods of Jupiter, Saturn, Uranus and Neptune?

EDIT: Code in Python 2.7:

from datetime import datetime, timedelta
from skyfield.framelib import ecliptic_frame

def f(t):
sun_eph = eph['sun']
s_eph = eph['saturn barycenter']
_, s_lon, _ = sun_eph.at(t).observe(s_eph).frame_latlon(ecliptic_frame)
s_angle = s_lon._degrees
print("s_angle = ", s_angle)

t0 = ts.utc(-13188, 8, 11, 14, 4)
f(t0)
# ('s_angle = ', 1.7441721183417348e-05)
t1 = ts.utc(1878, 10, 8, 3, 55)
f(t1)
# ('s_angle = ', 1.4075963901504881e-05)
(t1-t0)/512.0
# 10747.657377115886


Indeed there was error somewhere, now I got another number, but it still is not equal to that of Wikipedia.

• Not only Wikipedia, Nasa's website also states the same number, check here nssdc.gsfc.nasa.gov/planetary/factsheet/saturnfact.html, Even tropical year of saturn is 10,746.94 earth days only Jan 20, 2022 at 14:29
• I think you are looking for accuracy, not precision . Jan 20, 2022 at 15:22
• It would be better if you had shown your calculation. You might well have made a mistake, and there's no way to tell. Jan 20, 2022 at 20:11
• This may be helpful: Nuances of the terms (mean / osculating / Keplerian / orbital) elements Jan 21, 2022 at 21:13