The modern calendar is a solar calendar, based on the 365 days required for the earth to orbit the sun.
(The modern calendar; is; a solar calendar, based on the 365 days) (a solar calendar; based; on the 365 days) (the 365 days; required; for the earth; to orbit the sun)
The modern calendar a solar calendar the 365 days
is based required
a solar calendar, based on the 365 days
on the 365 days
for the earth to orbit the sun