Convert Month (month) to Year (Sidereal) (y (sidereal)) instantly.
About these units
Month (month)
A month traditionally reflects the lunar cycle, which lasts about 29.53 days (a synodic month). Ancient cultures used lunar months to track seasons, religious festivals, and agricultural cycles. In modern civil calendars, however, months are fixed lengths of 28–31 days to maintain alignment with the solar year. This creates a hybrid system: culturally grounded in the Moon, yet functionally tied to Earth's orbit around the Sun. Months remain one of the most intuitive time units for planning—budget cycles, billing periods, academic schedules, subscription systems, and medical dosing regimens all rely heavily on monthly intervals.
Year (Sidereal) (y (sidereal))
A sidereal year is the time it takes Earth to complete one full orbit relative to distant fixed stars, lasting approximately 365.25636 days. This is the "true" orbital period of Earth in space, unaffected by precession-related shifts of the equinoxes. Sidereal years are used in celestial mechanics, spacecraft navigation, and modeling solar system dynamics. The slight difference between the tropical and sidereal year (about 20 minutes) reveals how Earth's wobbling axis alters how we perceive time, creating two distinct astronomical year definitions.