Using PyEphem, I calculated the time difference between consecutive summer solstices in the south hemisphere for the last 4000 years, and plotted them in a graph. It seems like random noise around the mean, but the amplitude seems to oscilate with a period of around ~161 years. What explains this behavior?
Code used:
import ephem
date = ephem.Date("2023/01/01")
solstice = ephem.previous_winter_solstice(date)
for i in range(4000):
previous_solstice = ephem.previous_winter_solstice(solstice)
print(solstice - previous_solstice)
solstice = previous_solstice