A year is a time interval approximately equal to the period of the Earth's rotation around the Sun. ... 2) a tropical year is a time interval between the Sun's two centre successive passing through the medium point of the vernal equinox (365,2422 days); . 3) anomalistic year is a time interval between the Sun's two centre successive passing through the perihelion of its visible heliocentric orbit (365,2596 days); . ... 6) lunar year includes 12 lunar synodic months (about 354, 367 days); . ...