How does gravity influence our annual calendar?

It is influenced by the uncertainty of non fixed status of annual calendar that is due to the presence of gravitational pull from the Moon.

Explanation:

The tidal forces are generated over the Earth by the Sun as the solar tides and lunar tides. The revolution of moon across Earth changes every month as the path taken by the moon is elliptical in nature. So the day and night varies in length by each month.

Therefore the annual calendar is affected by the gravity influenced by the moon with tidal formation of varied length causing the time to fluctuate. This fluctuation hence results in varied annual calendar.